Questions & Answers
Aspen Trees

This page contains questions (edited) we have received from our viewers along with our responses.  
We thought you might find this information helpful.        

Q:    We have had an extremely mild winter, no snow and warm.  I just noticed that my six year old aspens have those fuzzy little pussywillows on the branches. I usually don't see these until April right before they leaf out. What happens if they leaf out too early? Will it kill the tree? Is there anything I can do?  J. J., Bozeman, MT; 1/28/12
A:    If the aspens leaf out early a spring frost will probably kill the leaves, but not the tree. The tree will produce a new set of leaves. The health of the tree will be in danger if this happens repeatedly throughout late winter and spring.

   We recently purchased an aspen tree that appears to have been cut from a root system. The base of the tree is approximately 2-3 inches in diameter and the cut off roots are approximately 1 inch in diameter and only 4-6 inches long. It does not appear that there are any real "live" roots that would be sucking up water. The dirt that was around the base fell apart as we were placing tree in the hole we dug in our yard. Did we get "taken" by someone who just went into the forest and dug up a bunch of shoots? We are watering the tree every 3rd day or so but the few roots that are present don't seem to be taking. Thanks for any help.  B. H., Santa Fe, NM; 9/25/11

A:    There is a good chance the aspen tree won't survive. Water it regularly while the weather permits. Also, water it about twice a month in winter when there is no snow on the ground. Like you, I suspect the aspen was recently dug up and planted in the pot.

   We planted five quaking aspens in our front yard in early August.  They are planted in full sun with south facing exposure.  We are watering them 30 minutes a night on our drip system.  Two weeks ago, the leaves started to look burnt around the edges, and now many of the leaves are brown and dead looking.  What can we do to help our trees?  We realize that the time of year we planted combined with the full sun exposure are not ideal, yet many of our neighbors have aspens and they are thriving in similar conditions. Will our Aspens survive?  What can we do?  Thank you so much for your help!  K. M., Denver, 9/17/11

A:    The roots of newly planted trees need time to become established and grow before they can absorb sufficient water for the tree. Planting trees in hot weather adds to the challenge. Check to see if the soil is getting wet several inches deep when the trees are watered. Water the trees so that the soil is soaked, then allow it to dry out until it is just slightly moist before watering again. Be sure to water the trees once or twice a month this winter when there is no snow on the ground.

   I have four Aspens.  On one the leaves are changing to a red color with red veins. A portion of the trunk has a shiny sticky material that seems to attract bugs. I drip water for three hours every three days. We are at the base of a mountain range at 4500'.  K. C., Winnemucca, NV; 7/14/11

   The shiny, sticky material on the trunk is a concern because it could be a sign of poplar borers. Spraying the trunk with an insecticide in July and August can help with control.

   I have two Aspen trees approx 20ft in height and over the past 14 years they have grown rapidly and both have beautiful crowns.  This year one has small objects on the bark that when viewed up close have the shape and size of sesame seeds and are brown/black in color.  They are primarily on the SE side of the trunk.  I would hate to lose these trees...are they in danger?  b. s., Falcon, 5/7/11

   It sounds like the aspen trees may have oystershell scale, a common pest on aspens.  The crawler stage is from early May to June.  Spray the trees with an insecticide for scale.  Then during winter, spray the trees with horticultural (dormant) oil to kill over-wintering scale.
Q:    I am about to build a geodesic dome greenhouse very near an aspen grove (well most of my property is an aspen grove).  There will be no foundation to speak of and I am quite concerned that the aspens will want to sprout up inside.  If I put in some metal flashing around the perimeter down to about 18 inches will that stop the root system from invading my greenhouse?  L. K., Pine, 2/16/11
   The metal flashing will definitely deter the roots from invading the greenhouse, but there is no guarantee they won't eventually make their way inside.  If you can sink the flashing down to 24 inches it would be even better.

   My aspen trees didn't drop their leaves this fall. It is now February, do I need to manually remove them?  2/7/11

   It is quite common for aspen leaves to freeze on the tree before dropping off.  Wait until the end of winter when the weather is above 45 degrees and spray the tree with a strong jet of water to knock off the dead leaves.  Do this in the morning so the tree can dry off before it gets cold at night.

   I looked through the aspen questions but didn't see anything quite like this.  Our aspens have a yellow foam on them.  There was even a chunk of the foam on our lawn this morning.  When I take a stick and remove the foam from the trees, it is greenish underneath.  Any idea what this is?  Thank you!  R. B., Fort Collins, 7/17/10

   It sounds like the aspen has bacterial wetwood (slime flux).  Unfortunately there aren't any sprays that cure it that I am aware of.

   We have a fairly large aspen tree in our backyard.  It budded in the spring - a couple of branches leafed out and the rest have not.  The buds seems to be drying out now.  What happened?  C. S., 6/17/10

A:    The aspen tree may have been damaged by weather, insects, disease, or root problems.  It would need to be thoroughly inspected to determine the cause. 

   We transplanted some aspen trees and the next day their leaves started to wilt. We have been watering them regularly for about 30 minutes a night.  Are the trees just recovering from the move or are they in trouble?  What should I do to help them?  Fertilize?  What kind is best?  R., 6/2/10

A:    The newly planted aspen trees are going through transplant shock.  You are watering them too much.  Let the soil dry out until it is just barely moist before watering again.  Do not fertilize the trees.  (You should wait until next spring to fertilize them.)

   I live at 6100' in SE Idaho.  I have hundreds of Quaking Aspen on my 5 acres.  The older ones seem to be in trouble.  Many have died while the young are thriving.  When cut down, I find loose bark and underneath worm type lines.  If some pest, how can I treat and prevent.  Thanks, we love them and want to save them.  B. S., Inkom, ID; 5/20/10

   The worm-type lines could be a symptom of borers.  Spraying the trunks and large limbs with an insecticide in early summer when the adults are active on the surface of the tree may provide some control.  Look for a product whose label says it can be used on aspens to treat poplar borers or other borers.

   Hi, I have several aspen trees.  Last year, something (a bird or squirrel?) tore off strips of bark from the trunks of several tree, effectively girdling the trees.  As a result, the portions of the aspen above the girdle now seem to be dead.  Do you know what might have caused this, and how I can prevent it from happening again?  C. W., Denver, 5/15/10

   If the strips of bark were removed near the bottom of the tree trunks, voles could be the culprit.  If they were higher up the trunks, squirrels may be responsible.  You might try placing wire mesh around the trunks to protect them.

   I am purchasing a property in Red Feather Lakes that is mostly a dense stand of lodgepole pine.  The large clearing for the cabin has some scraggly aspen.  Is there anyway to promote the growth of the aspen?  T. C., Red Feather Lakes, 2/27/10

   You can promote the growth of aspens by providing plenty of water for them.  Fertilize them in spring.

   We bought a house in Denver 7 years ago with 3 Aspen trees in the back yard.  Each spring, they emit their cottony seeds for a good month or so.  Then they get aphids.  Though I try to hose them off, they persist, and then a sooty mold develops and drops down on the plants beneath.  Plus they send their shoots up all over the yard.  I've tried to take good care of these trees, but the leaves look healthy for only a brief period.
   Since we're on a small city lot, and space is at a premium, I'm seriously considering having the trees removed.  The arborist I spoke to recommended using Tordon on the three stumps to keep the roots from sprouting.  I'd rather not use any sort of herbicide unless it's absolutely necessary.  Would the aspens keep sprouting from the roots in the yard even after the stumps have been ground down? For how long?  If I choose not to use the Tordon, how much of a hassle can I expect?  Many thanks for your help.  L. A., Denver, 12/4/09

   Removing aspens can be a challenge.  They will sprout shoots from the stump and the roots -- lots of them --for many months.  This can be a major nuisance.  Therefore, use of an herbicide is often recommended.  I share your concerns regarding the use of chemicals, which often have a negative impact on the environment.  It can be a hard decision to make.
Q:    This spring I planted a 6-foot tall aspen in my yard. It looked very healthy most of the summer. Recently, its leaves appear light green. I have the tree irrigated every day for about 30 minutes on a drip feed. The soil in the area tends toward clay. Could I be over-watering this tree to cause the light green leaves?  C. C., Steamboat Springs; 8/31/09
   Watering daily is likely too much.  The soil should be allowed to dry out slightly between waterings.
Q:    Every year my Aspen trees get covered in massive webbing full of worms.  Help.  Last year I cut all the tops of the trees that were infected, but if I keep this up I won't have much of a tree left. What can I do to get rid of these critters?  Thank you,  C. R., Edgewood, NM; 8/12/09
   The webbing is probably caused by tent caterpillars.  You can control them by removing the tents that contain the larvae, spraying the trees with horticultural (dormant) oil in winter or early spring and/or spraying the trees with insecticide in spring and early summer when caterpillars are present.
Q:    One of our columnar aspens has a patch about 6 inches by 6 inches of holes drilled a little ways into the bark. The holes are in a very regular pattern and are only about 1/4 inch across. What might cause this?  C. E., High Level, AB; 8/2/09
   Woodpeckers/sapsuckers may be drilling the holes in the aspen tree.  The woodpeckers or sapsuckers may be feeding on insects inside or on the bark, but not necessarily.  They will also drum on trees to establish territory, attract mates or feed on tree sap.  For tips on controlling them please see
Q:    I have a mature aspen tree that has developed rough bark near the mid section of the tree. With closer inspection, the rough area seems to be small black lines (approx 1/32 of an inch in length and very thin that can be scraped off with my finger nail. This appears to be spreading. Will this kill the tree? Is there anything I can do?  B. L. 7/1/09
   It sounds like the aspen tree has a pest called scale.  Clean up fallen leaves this fall, spray the tree with horticultural (dormant) oil in winter and spray the trunk with insecticide in June next spring to control this pest.
Q:    We have a lot of Aspens and this year some of them have a huge amount of cotton seed things hanging from the leaves. I don't remember them doing this so badly, and it's messy. What's causing this?  It's only a few of my trees.  J. L., Evergreen; 6/22/09
   Aspens are members of the poplar family.  Many members of this family produce catkins that contain seeds in spring.  Weather conditions and the overall health of the trees can encourage production of catkins.
Q:    It is late April and my aspens have just leafed out in the last week or so.  I just noticed one of them has black spots on the centers of most of the leaves, which aren't even completely filled out yet.  It seems too early for ink spots or other pests. Can this be caused by a late freeze hitting this tree at a specific point in its leafing process, as again the other two seem totally unaffected? We did have a very heavy snow and late freeze in the last few weeks as you probably know. Thank you.  F. S., Superior, 4/26/09
   You are correct.  The black spots on the leaves are more than likely due to the freeze we had recently.  Foliar diseases at this time of the year are rare.
Q:    I live in North Georgia and planted an Aspen tree I ordered three years ago. We're in area 6. It lives, has leaves, but hasn't grown any. What can I do to the soil to perhaps help it along?  W. V., Atlanta, GA; 2/19/09
A:    To promote growth, water the aspen generously.  Aspens like plenty of water.  Also, aspens benefit from being fertilized in spring.  Use a general purpose fertilizer labeled for use on trees.
Q:    There is someone who lives nearby who has a great looking strand of aspens, and I was thinking of asking if I could dig up a small clump for planting in my yard. Is this a feasible way to plant aspens, and if so, what steps should I take when digging them up (w/ owners permission). Also, when is a good time of year to do this transplant, or to just plant aspens in general?  S. D., Evergreen, 1/2/09
   When transplanting a tree you want to dig up as much of the rootball as possible.  Most roots grow in the first twelve inches or so of the soil and spread over a wide distance (equal to or greater than the tree's height).  Keep that in mind when digging up the trees.  You can wrap the root ball in burlap, a tarp, or sturdy plastic sheet to transport it.  The trees should be planted immediately.  The hole should be the same depth as the rootball and at least twice the width.  Build up a basin with soil around the tree and fill it with water.  Water each tree immediately as you plant it.  Keep the soil moist, not soggy.  The best time to transplant the trees is early spring.
Q:    I have an aspen tree in the front yard.  I noticed since the leaves are off of it that some of the branches have like swollen places on them as if it were ballooning out in places. The tree seemed to be real healthy all summer. Is this a normal thing or is it a sign of a disease.  B. H., Rifle, 11/22/08
A:    The bumps, or bulges, you described are very common on aspen trees.  They are called poplar twiggalls.  They are created when the poplar twiggall fly inserts eggs in developing stems.  Larvae hatch and feed within the stem, causing the swollen gall.  Fortunately, these galls do not threaten the health of the tree. There are no effective chemical controls to prevent galls, although predators such as birds and parasitic wasps are good natural controls.
Q:    Great site. Good information. I live in Cheyenne, Wyoming. The aspens in our yard are beginning to thin out due to their age. I would like to replace them as I love the look. I planted a clump of aspen (3) on the east side of the house in a protected area. They looked very healthy when planted and for the rest of the first season. This year the tree leafed out (very green leaves) and now the branches have begun to wilt. It still looks healthy but very weak. Is it the heat from that side of the house? The trees were only fertilized once in the spring with Miracle Grow.  D. J., Cheyenne, WY; 8/10/08
   Wilting can be caused by too much water, too little water, poor drainage and other factors.  When we see a plant wilt we usually assume the plant needs more water and may end up over-watering the plant.  Let the soil dry out until it is just barely moist before watering.  When you water, soak the soil thoroughly to encourage deep root growth.  Avoid using weed killers near the trees or in area where the roots are growing.  Be sure to water periodically in winter.
Q:    I have an Aspen that is about 20 years old and has been very healthy until recently. The leaves on my Aspen have started to fall off in large amounts, similar to the fall leaves dropping. When the leaves fall they are green, but quickly turn spotted and black after falling off. The only thing that I noticed are the small holes in the leaves before they fall. Any suggestions? K. N., Colorado Springs, 8/4/08
A:    Try to improve the vigor of the aspen tree by keeping it well watered and fertilizing it in spring.  The small holes are possibly due to a fungus called "Ink Spot."  This disease causes early leaf drop.  To control the disease rake up fallen leaves.  The fungus over-winters in fallen leaves and re-infects the tree in spring.  You may also want to consider spraying the tree with a fungicide in early spring.
Q:    This is a very informative and interesting site, answering our question about the sucker shoots and the inability to control them. We are considering removing the trees because of this and replacing them with something else. What is the best way to remove them and kill the root system so that we no longer have sucker shoots growing all over our lawn?  T. C., Grand Junction; 8/3/08
   I assume the trees producing the shoots are aspens.  For tips on removing the aspen trees please see
Q:    One of our aspen trees has a sticky substance on the leaves. The patio area under the aspen has been covered with this as well. What could this be?  S. H., Sandy, UT; 7/16/08
   The aspens have aphids which secrete sticky "honeydew," and probably are causing the leaves to curl.  You can spray the trees with a strong jet of water or insecticidal soap, or you can use a systemic insecticide for control.
Q:    Hello...We travel to Colorado every summer and love the aspen trees! We are from Omaha, Nebraska, and would love to plant some aspen trees in our backyard. We have been told that the Prairie Gold Aspen would be a good choice for our area. Would you agree with this? Any thoughts you might have would be greatly appreciated. Thank you!!!  K. P., Bennington, NE; 7/2/08
A:    The Prairie Gold Aspen would be a good choice because it is a Nebraska native.  That means it is adapted to the soil and climate of your area.  You do not want to buy aspens from Colorado because they are best suited to the mountains.
Q:    We have so many little aspen roots popping up everywhere!  How do you tame the beasts?  B. K., Milliken, 5/19/08
   It is really difficult to control aspen shoots that develop on aspen roots.  When they're little you can keep them mowed off in the lawn.  In beds you can try to pull them or snip them off when they're little.  Herbicides should not be used because they can travel through the roots and harm the parent tree.  There is a product called Sucker Stopper that may help.
Q:    We have a large Quaking Aspen tree in our yard that is in full bud and looks very healthy. However, there is, what looks like, about an inch long cut on the trunk that runs horizontal to the tree and has quite a bit of sap running out of the cut. What would cause this and is this a threat to the tree's health?  S. R., Bayfield, 4/8/08
A:    The cut in the aspen tree may have been caused by a rapid drop in temperature (frost crack), sunscald, mechanical injury or other cause.  The wound should gradually heal.  Any wound makes a tree more susceptible to an attack by disease organisms or pests.  Keep an eye on it and treat with a pesticide or fungicide if necessary.
Q:    What is the best method of cutting down an aspen without damaging the others around it? Previous owners did not cut off support ties, which caused the aspen to be strangled. Once I cut the support ties off it appears to be dead. Is there a way to bring back strangled aspen without cutting it down?  J., Loveland, 2/28/08
A:    I suggest that you wait to see if the aspen tree leafs out in spring before cutting it down.  Water it regularly when there isn't any snow on the ground.  Fertilize the tree in April.  If it doesn't leaf out by late May it probably is dead.  You can cut it down with a handsaw if the trunk isn't too big, or you can use a chainsaw.
Q:    I would like to start off by saying that your Q&A page is great!  I have 6 Quaking Aspens planted around my yard and I was wondering if there is anything I can do to help them show their beautiful fall color.  Having planted them here in the city the leaves just turn brown in fall, and then fall off.  I planted them to have the fall color and sadly I don't see it...  M., Thornton, 8/19/07
   Unfortunately, there is little you can do to get the aspen trees to show fall color.  The shorter amount of daylight in fall and cool temperatures are two factors that lead to fall color.  In September you can try gradually reducing the amount of water the trees receive to see if that helps.
Q:    The ends of the leaves on our aspen trees are turning brown.  What is wrong with them?  A., Clifton, 8/2/07
   The edges of leaves may turn brown due to a build-up of salt in the soil.  It may also be due to leaf scorch in hot weather.  Salt levels can be aggravated by drought, the use of fertilizers, and other factors.  Leach the salt out of a tree's root zone by soaking the area thoroughly with water.  Try to keep the trees watered regularly, allowing the soil to dry out between waterings.
Q:    The following is a tip on rejuvenating aspen trees from a visitor to the Colorado Gardening website.
A: HI,
We have aspens in our yard front and back in Parker, Colorado. When we moved into our house 3 years ago, the aspens looked very poor, with dead branches and small light green leaves. One of the trees had the orange streaks going down the trunk. That tree eventually died. They all had large bumps or enlarged areas on the trunks and branches. These trees are approx. 10 years old and 20 to 30 feet tall. Two years ago I started a regimen of applying BAYER TREE AND SCRUB INSECT CONTROL in the fall. {This can be purchased at Wal-Mart approx. $20.00.} It's in liquid concentrate and you mix it with water and pour it around the base of each tree. In the spring I started using MIRACLE GROW GRANULAR FERTILIZER.  This feeds the tree for approx. 3 months. The trees this spring and into the summer 2007 are text book beautiful!!!! Big dark green leaves, no dead branches, excellent new growth, totally  healthy. I hope this info will help others with similar problems. H. B., Parker, 7/22/07
Q:    My aspens have a few branches that the leaf color is fading to a lighter color and the veins in the leaf then appear prominent.  The leaves otherwise appear healthy and I do not see any bugs.  Is this a sign of a fungus or insect infestation?  K. O., Parker, 7/7/07
A:    Pale leaf color combined with dark green veins can be a sign of iron chlorosis.  This is a condition that occurs when plants are unable to absorb sufficient iron from the soil.  It is very common in Colorado.  Apply chelated iron to correct the problem.  You will find this product at garden centers.
Q:    We recently planted 20 Aspens along our front driveway.  Most of the trees are doing well, but some of them appear to be dying, or not as healthy as the others.  Our soil tends towards clay.  We are watering about once a week.  My questions are:  Are we watering enough?  Are the trees still trying to get "acclimatized" to being recently planted?  Are they dying?  L. B.; Peyton, 7/5/07
   It takes several months for trees to become established.  During that time they require extra water.  Watering once a week may not be enough, especially in hot weather.  Aspens like lots of water.  Soak the soil thoroughly, then let the soil become almost dry before watering again.  Deep watering encourages roots to grow deeper.
Q:    Our neighbors have several Aspen trees growing along the fence line of our backyard.  We just moved in so I am not sure of their age but they are around 15’ tall.  The trees seem healthy and provide privacy during the summer months but they are beginning to obstruct our views of the mountains.  I wanted to know if we could maintain their current height with pruning/trimming without causing any damage to the trees?  Any tips on what we should/should not do?  Thanks, B. F., Parker, 6/30/07
A:    Thinning cuts are the recommended method for maintaining a bit of a view.  Topping the trees is strongly discouraged because it creates weak, unnatural-looking growth that breaks easily.  Wait until winter to prune the aspen trees.  They are prone to getting diseases and/or pests when pruned in summer.
Q:    I live in Brighton, CO, and I recently purchased three new Quaking Aspen trees.  The two in the backyard went through a brief hard-time, but I set up a patio umbrella over them and they seem to be doing great.  The front Aspen (facing North) was doing great at first, but now the leaves on two of the 4 trunks are turning yellow, crispy and falling off.  Some of the other leaves are doing this on the other trunks.  Is there anything I can do to remedy the situation and get the Aspen thriving again?  Excellent site and thanks for your help!  S. N., Brighton, 6/16/07
A:    The aspens are going through transplant shock as they adjust to being planted.  Recent hot, windy days aren't helping the situation!  Water the trees thoroughly and then wait to water again when the top of the soil is only slightly moist.  Do not keep the soil constantly wet.  (When a newly planted tree or shrub shows signs of distress many gardeners tend to over-water, drowning the plant.)  A layer of mulch around the trunk will help the soil retain moisture.
Q:    Your Q&A is a great information source, thanks. Our neighbors are replacing their wooden fence with a stucco wall so we removed our bushes & trees to facilitate the work. We're planning to plant a number of small Aspen trees along the new wall, but the neighbors have expressed concerns that the Aspens may damage their wall and have advised us to plant the Aspens as far away from the wall as possible. As the area where we want to plant the Aspens is quite narrow, we want to plant the Aspens as close as possible. Could you tell me if there are guidelines/laws that dictate minimum distance to neighboring property lines and should we be concerned about the Aspen's invasive character? Much appreciated, C. V., Denver, 5/23/07
   I don't know if Denver has guidelines/laws regarding planting distances from property lines.  The crown of almost any tree planted close to the wall will extend into the neighbor's yard -- creating a potential problem.  The aspens' invasive roots may eventually find their way under the wall and into the neighbor's yard.  Once there they are likely to produce numerous suckers (little shoots) in their lawn and shrub/flower beds.  They'll do the same thing in your yard.  The trees produce catkins in spring that can be messy.  Aspens are prone to diseases and problems with insects.  They are short-lived trees.  I encourage you to select something else.
Q:    I live in Boulder, CO, and have two Aspen trees growing in the front lawn. They are growing suckers and protruding throughout the lawn. Is there a way to get rid of these suckers without having to uproot the trees or killing the lawn?
Thanks for your help!  A., Boulder, 5/7/07
   Unfortunately, there is no easy way to control aspen suckers.  Herbicides would possibly harm both the tree and the lawn.  A hint: The smaller they are the easier it is to mow or snap them off. 
Q:    Our neighbor has two large aspen trees that have something growing all over the bare branches this spring. These are well established trees. I really don't know how to describe it but I'll do the best I can. They hang from every branch. They are furry and about two inches in length. At the top part connecting to each branch is a reddish brown head and from the head it looks like a long stretched out caterpillar. The trees have no new leaves at all. What is this gross infestation? We have never seen this before. We are writing from Ruidoso, New Mexico about 7500 Elev. What has happen to our Aspens? And is it too late? J. S., Ruidoso, NM; 5/3/07
   Your aspen trees do not have an infestation.  The furry things are catkins which aspens, cottonwoods and a few other trees produce in spring.  They contain seeds.  They can be an unattractive nuisance, but they will soon disappear
Q:    I have a young quaking aspen here in central Colorado and its beginning to bud what looks like small fuzzy gray buds...I am curious if this is normal.  D., Castle Rock, 3/16/07
   The fuzzy gray buds on the aspen trees are normal.  Aspen trees have catkins and the fluffy cotton they produce contains seeds.
Q:    I have aspens on my property and would like to introduce more aspens to a different area in the yard (where they are presently not growing).  I would like to transplant the aspen suckers that are prolific near their parents. Can I do this or do I have to transplant a full, mature tree? What is the minimum height/width requirement for an aspen able to withstand a transplant? (I live at ~8,000' in CO, west of Denver).  Thank you so much for your time!  N., Idaho Springs, 2/8/07
A:     You can transplant the aspen suckers.  Get as much of the root system as possible when you dig them up.  Small transplants tend to be more successful than larger ones.  There is no minimum size.  Keep the soil slightly moist while they are taking root.  Plant the transplants in spring, not in summer when the weather is hot.
Q:    When is a good time to prune Aspen trees?  I have Aspen trees that have some dead branches, but I don't want to trim them in the wrong season and cause harm to the trees.  T., Colorado Springs, 1/28/07
A:   You can prune the aspen trees in late winter or early spring before they leaf out.
Q:    I just read through the q&a for aspen trees.  I live in Boise, ID, and would like to plant three aspens in my front yard.  This is a south-facing area, without much shade during the day.  Will the aspens be able to withstand 100 degree heat and sun in the summer?  Thanks.  H. H., Boise, ID; 10/10/06
    Many people in Colorado plant aspens in the conditions you described.  However, they end up with problems.  The trees are highly susceptible to pests and diseases.  The roots produce sprouts in the lawn and flower beds.  Although the aspens would live in the heat and sun, I strongly encourage you to plant another kind of tree.
Q:    We bought 6 aspen trees in June.  We live in Black Forest, CO.  Five look healthy, but all six have bumps all over the leaves.  Is there any way to get rid of those next year? 
   One of the trees has lost all of its leaves but doesn't appear to be dead.  Is there something I can do to encourage leaf growth next spring?  S. A., Black Forest, 8/1/06
    The bumps, called galls, on the aspen leaves are caused by eriophyid mites.  The trees can be sprayed with Sevin to control the mites.  Spraying the trees with horticultural (dormant) oil in late winter can also help control them.  To encourage leaf growth next spring be sure to water the trees once or twice a month during winter when the ground isn't frozen.  You can also fertilize the trees in spring.
Q:    We transplanted 2 aspens in May this year. Can they go into shock?   With both trees the leaves died and the branches are crisp/looks dead, but the base of both trees are green/white. The base looks healthy.  D., 7/21/06
    Yes, newly planted trees can go into transplant shock, especially when the weather is hot.  Water the aspens regularly.  Soak the soil and then allow it to dry out almost completely before watering again.  Do not keep the soil soggy.  Hopefully the trees will recover, although it may take awhile.
Q:   I live in Monument, Colorado.  For the past couple of years my neighbor and I have noticed bores in our Aspen trees.  The trees heavily sap at the site of the small little holes.  Many holes can be found on a single tree, no matter what the age of the tree.  What are these and how do we treat them?  K. W., Monument, 5/25/06
A:     The little holes in the aspen are the work of poplar borers.  The adult is a grey beetle that can be found on aspen trees in summer.  The greatest damage to the tree is caused by the larvae which tunnel into the tree and continue to tunnel within the tree.  Insecticides, such as Sevin (Carbaryl) or Permethrin, applied to the trunk in summer can kill the exposed adults.
Q:    Hello, I have a couple of questions on transplanting aspen trees. We have just gotten a permit here in Pagosa Springs, CO, to dig up 4 Aspen trees here in the National Forrest.  How much root ball is required for a 4 or 5 foot aspen tree?  And what is the best way to "wrap" the root ball?  And the best way to "re-plant"?  Thank you, K. S.; Pagosa Springs; 11/28/05
A:     When transplanting a tree you want to dig up as much of the rootball as possible.  Most roots grow in the first twelve inches or so of the soil and spread over a wide distance (equal to or greater than the tree's height).  Keep that in mind when digging up the trees.  You can wrap the root ball in burlap, a tarp, or sturdy plastic sheet to transport it.  The trees should be planted immediately.  The hole should be the same depth as the rootball and at least twice the width.  Build up a basin with soil around the tree and fill it with water.  Water each tree immediately as you plant it.  Keep the soil moist, not soggy.  The best time to transplant the trees is early spring.
Q:    Which colors come first when Aspens start to turn color in Autumn?  What is the progression of colors through the leaves falling off?  J. P., 10/12/05
A:   Unlike the vibrant variety of colors seen in the hardwood forests of the eastern part of the United States, aspen groves are primarily yellow in fall.  The leaves gradually change from green to yellow and darken to a deeper shade of gold.  A bit of orange is also present.
Q:    My aspens and I live at 4500' in central Oregon. We are both quite healthy but these are the only aspens I have ever known that don't have a colorful fall foliage. The leaves merely turn black with the onset of below freezing weather and then the leaves stay on the trees like that all winter. Is there anything I can supplement them with to encourage some pretty colors in the Fall?  Thank you for your wonderful website.  W. P., Fort Rock, OR;10/12/05
A:    Unfortunately, there is little you can do to promote fall color.  Cool temperatures are what cause the leaves to become yellow.  Early freezes are what kill green leaves, causing them to wither without falling off the tree.
Q:    I have an Aspen tree that failed to leaf this spring.  The bottom of the tree did fine.  Based on your information, I'm assuming the tree has a fungus.  Is there anything I can do this fall - besides removing the dropped leaves?  S. K., Highlands Ranch, 9/15/05
A:    Try to improve the vigor of the aspen tree.  This fall be sure to remove dropped leaves to prevent disease organisms from over-wintering and re-infecting the tree.  Winter watering if there is little snow also may help.  You might want to spray the tree in late winter or early spring with horticultural (dormant) oil to kill over-wintering pests.  If the tree's leaves showed signs of disease this year you might want to spray the tree with a fungicide right after the tree leafs out in spring.  Fertilize the tree in spring.
Q:    Are there any relatively non-toxic ways to treat scale on Aspen trees?  If not, how would a poison fearing person need to remedy this situation w/o calling in the professionals?  M. S., Aspen, 8/7/05
A:     A relatively non-toxic way to control scale is to spray the trees with horticultural (dormant) oil in late winter or early spring.  The oil suffocates the scale and other pests that over-winter on the trees.
Q:    Will aphids kill aspen trees if left untreated?  Will strong rains help with the aphid problem?  C. M., Snowmass Village, 8/1/05
A:     The aphids themselves probably won't kill the aspen trees.  However, they may weaken the trees, making them more susceptible to other pests and diseases.  Strong rains and spraying the trees with a strong jet of water will wash off many of the aphids.
Q:    I have an older established aspen in my front yard.  It was here when I bought my house six years ago.  I have tried everything to get it to look good.  I have fertilized it in the spring, I have raked up all of the leaves in the fall, and I have continually put insecticides and fungicides on the tree.  It still gets the same black and rusty looking leaves and dead branches every year.  I also give it plenty of water throughout the summer.  What am I doing wrong?  The tree never looks very healthy.  I am tempted to get it taken out, and try a different tree.  Thank You.  B. B.; Cheyenne, WY; 7/26/05
A:    It sounds like you are doing everything possible to help the aspen tree thrive.  Because it is not responding to your efforts and is an older tree, taking it out may be the best option.
Q:    I have noticed an orange tint along the main trunk of many aspen trees this year - both in my yard and on Forest Service property.  What type of fungus is this and is there anything that I can spray on the tree to help.  The orange spots seem to be a little soft to the touch also.  Eventually the whole trunk turns orange or orangish/pinkish and the tree dies.  S. R., Indian Hills, 6/14/05
A:     Orange tint on the trunk or branches of aspen trees is often a sign of a disease, cytospora canker.  Cytospora canker is caused by a fungus.  To control the disease, improve plant vigor by fertilizing the trees in spring, providing ample water, and pruning only when the trees are dormant.  Prune off branches that become diseased and remove dead bark from the infected area.
Q:    I have several large Aspens approximately 12 years old. After a severe hail storm 4 years ago the trees have experienced leaf blight and borers. This year the leaves now have clumps that look like cabbage. Any ideas?  B. D., Black Forest, 6/10/05
A:     The distorted leaves may have been caused by Poplar Vagabond Aphids.  This aphid flies to the tree in fall and lays eggs in bark crevices.  The eggs over-winter on the tree and hatch in spring.  They feed on twigs, creating galls.  Winged aphids leave the tree in spring and summer.  Spray the trees in late winter with dormant (horticultural) oil to kill over-wintering eggs.
Q:    Help.  My Aspen trees are about 5 years old, and have numerous "bumps" or bulges on their branches,  It started with one tree, and over the past year spread to the others.  Any suggestions????  C. L., Aurora, 3/5/05
A:    The bumps, or bulges, you described are very common on aspen trees.  They are called poplar twiggalls.  They are created when the poplar twiggall fly inserts eggs in developing stems.  Larvae hatch and feed within the stem, causing the swollen gall.  Fortunately, these galls do not threaten the health of the tree. There are no effective chemical controls to prevent galls, although predators such as birds and parasitic wasps are good natural controls.
Q:    We are planting about 300 Aspens on the West on our land in Wyoming.  There are existing Aspens on the land and we want to extend their presence.  Do you have any recommendations on planting?  We would like to plant just small 1-5 gal tree to start. S. D., Weston, CT; 2/25/05
A:    The best time to plant the aspen trees is spring.  Dig wide holes and take care not to plant the trees too deep.  Build up a basin around each tree and water the trees as you plant them.  They should be watered regularly until they become established.
Q:        My aspen trees have chronic aspen leaf disease...marssonina.  I need specific treatment besides raking the leaves.  I need a specific fungicide & whether they are sprayed dormant or spring.  Tks loads, A. G., Boulder, 2/4/05
   To control leaf diseases be sure to rake up the leaves.  Disease organisms over-winter on the fallen leaves.  When spring winds and rain arrive, the trees are re-infected.  You may also want to prune the true to open up the canopy.  This will improve air circulation.  Proper watering and fertilization will improve tree vigor, which enables the tree to cope better with problems. 
    Fungicides are usually sprayed at bud break.  Repeat the application two or three times, spraying every 12 - 14 days.  The following is a list of fungicides labeled for use on aspens to treat foliar diseases that I found in an article by the Utah Cooperative Extension:  Daconil 2787, Daconil Lawn & Garden Fungicide, Microcop, Copro, Kop-R-Spray, Kocide 101, and Champ.  Be sure to read and follow all label instructions.
Q:    I want to plant Aspens as a windbreak in my backyard.  I've heard the roots are invasive.  If I enclosed the area with a metal ring (landscape edging) that is approx 6" wide, would this help?
Thanks, C. B., Fort Collins, 2/8/05
A:     A 6" wide ring would be of limited help in confining aspen roots.  They will simply grow above and below it.  While aspens are beautiful trees they are prone to many problems.  You might want to select a different type of tree to use as a windbreak.  Evergreens such as Limber Pine (Pinus flexilis), Austrian Pine (Pinus nigra) and Rocky Mountain Juniper (Juniperus scopulorum) are useful as windbreaks.
Q:    I've heard that Aspen trees have one of the most extensive root systems in the world, making them "one of the worlds largest living organisms".  Is there any basis in fact to support this claim?  Does the root system interconnect?  Thanks.  C. G., Portland, OR; 11/28/04
    A quote from the booklet "Aspen: A Guide to Common Problems in Colorado" may answer your question:
    "Aspen is a clonal species.  Many stems grow from the same root system, so that it is possible for an entire hillside to be covered by one tree (biologically speaking)!"

Q:    Is the orange tone that shows up on aspens a disease? If so, is it treatable?  J., Colorado Springs, 10/12/04
    The orange tone on the aspens possibly is a disease.  If you see orange spots on the undersides of leaves, it is usually a leaf rust.  Rust can be managed by collecting and disposing of fallen leaves.  A fungicide labeled for treating rust in trees can be used if necessary.
    If the orange is on branches or the trunk it may be cytospora canker.  Keeping the tree healthy by proper watering may help the tree cope.
    If the tree has wounds that are oozing orange staining liquid, the problem may be poplar borers.  Insecticides are useful when adults are active on the surface of the trunk in summer (July & August).

Q:    We have three very healthy 3-year old aspen trees in our front yard, and we would like to keep them at their current height.  Can we top them?  If so, would early March be a good time to do this?  E. E., Pueblo, 10/9/04
A:     Topping trees is not recommended.  It results in weak, unnatural-looking growth that sprouts up and out from where the cuts were made.  It is better to shape the trees by pruning selected branches and thinning out branches.  If you decide to shape or thin the trees late winter or early spring (including March) are good times.  There are fewer disease organisms and insects around at that time of the year.

Q:    I planted three clumps of Aspens this past April. They seemed to be doing fine until mid August when their leaves started turning brown around the edges. The nursery from which I purchased them said I was watering them too much and to stop. I have, but the leaves are still brown and now some of the branches appear dead and break off. What do I need to do to make sure my trees don't die?  T. C., Lafayette, 9/23/04
A:     There are a few steps you can take to protect the health of the Aspens.  They like water, but don't over-water them.  Allow the soil to dry out slightly between waterings.  Water them at least once a month in winter when the ground isn't frozen.  Place a layer of mulch over the soil, but don't mound mulch up against the trunk.  When the leaves fall, rake them up and get rid of them.  Diseases and pests can over-winter in the leaves.  If there were any insects on the tree this summer, spray the trees with dormant oil before they leaf out in spring.  Do not fertilize the trees in fall.  They can be fertilized in spring.  To prevent sunscald wrap the trunks of the trees with tree wrap in late fall and remove the tree wrap in spring.

Q:    Hello. We are looking for the most informative and authoritative book on aspen trees. We are landscape contractors and need a reference guide for growth habits, diseases, fertilizing, etc. Can you please advise?  M. S., Tabernash, 8/14/04
A:     Colorado State University Cooperative Extension has an informative booklet on aspens.  It has information on growing aspens, diseases, etc. and photos that are helpful.  It costs only $5 and can be ordered online at  Click on Publications. Click on Gardening and Yard Publications.  Scroll to # 559A  "Aspen: A Guide to Common Problems in Colorado." 

Q:    I have a neighbor who has 3 big Aspen trees, and in his front yard he has a lot of shoots that are growing.  Now they are growing in my yard and I have to keep mowing my lawn.  Is there any way to get rid of these shoots?  There are so many.  Please help.  L. F., Arvada, 6/21/04
A:     Mowing or cutting off the shoots is about all you can do to control the Aspen shoots.  Herbicides would travel through the roots to the parent tree and damage it.

Q:    I have a large aspen tree that has a strange symptom.  The leaves have black spots all over them (which I have read about), but also are covered with a sticky, shiny coating, and are falling off still green.  I also have noted that the rocks underneath the tree have turned black.  Is there anything I can do?  And if there is a spray, how does one go about getting it to the top of a 40 ft tree?  B. T., Centennial, 6/13/04
    The leaves on the aspen tree probably have one of the leaf spot diseases that are common on aspen trees.  These are treated with a fungicide.
    The sticky, shiny coating is honeydew from aphids.  The honeydew has dripped onto the rocks.  Black sooty mold, which feeds on honeydew, is growing on the rocks.  You can spray a strong jet of water with the hose to get rid of aphids and the sooty mold.  Insecticidal soap or an insecticide can also be used for aphids.  A hose-end sprayer may be effective for the large tree.  If not, you might consider hiring a tree service.

Q:    I have a question regarding Aspen trees that I did not see answered in the Q&A section, which I have found very helpful - thank you.  We are between Deckers and Woodland Park, at about 7200 - 7500 feet and have some Aspens we are planting.  My favorite spot is adjacent to our leach field.  Will this be a problem due to their invasive root systems?  How far away from the leach field should we plant?  It is elevated from the leach field area, maybe about 5 feet and about possibly 5 feet away from where we think the leach field ends.  Thank you so much for your time.  K. M., Sedalia, 5/28/04
A:     I strongly suggest that you do not plant aspen trees near the leach field.  Aspen trees are a kind of Poplar tree.  Poplars are notorious for having invasive roots that clog pipelines.  Even if you could plant the trees 15 or 20 feet away, suckers are likely to sprout up and their root systems could create problems.

Q:    I have two Aspens in my back yard in Westminster.  They are both over 30 ft tall, age, unsure.  For the last 2 weeks or so I have watched an incredible amount of fine sap or resin drop down from the trees.  It forms a hard sticky surface on anything it contacts.  In the past couple of days, I've noticed aphids on the leaves.  Is the sap related to the aphids, and what can or should I do to remedy this situation?  B. R., Westminster, 5/19/04
A:    The sticky substance you described is honeydew that is secreted by the aphids.  To control the aphid population you can spray the trees with a heavy jet of water.  Or, you may want to use an insecticidal soap if the problem is fairly severe.  As a last resort you can use more potent chemical sprays.  However, you should avoid using stronger chemicals unless absolutely necessary because they kill beneficial insects as well as pests.

Q:    I have some Aspen trees in my back yard.  It appears that some type of insect that bores entered the bark all over the tree and bored up and then out another hole.  Sap has drained out this spring out of those holes.  Are my trees in danger of dying?  What can I do to prevent further damage?  J. M., Colorado Springs, 5/12/04
A:    Poplar borers can cause major damage to aspen trees.  The adults are grey beetles that emerge in late June and can be found on trees through August.  The females will begin laying eggs, so you want to kill them as soon as possible.  Spray the trees with an insecticide during those months to control the borers.

Q:    Help!!!  I planted a Quaking Aspen in my front yard, and the shoots are coming up everywhere in my yard, and now my neighbor's!  I've cut the tree down, and the shoots, of course, are still coming up.  I can't spray with Roundup 'cause they're in amongst the grass.  Is there ANY way to kill these things for good?  Any poison I can put down the stump?  ANYTHING????  Thanks so much for your great site, and your help with my problem!  T. F., Spokane, WA; 5/9/04
A:    Although you can't spray with Roundup, you can still use it to kill the sprouts and roots.  Let the sprouts get a few inches high.  Using a small paint brush or Q-tip, dab Round-up on some of the leaves of each sprout.  You should protect the lawn from drips.  Also, use Roundup on the stump.  This product will travel through the root system and kill it.  You may need to repeat this a few times. 

Q:    My landscapers are trying to fix the slope on my property and want to add soil in my "tiny" aspen grove which would mean adding about 12 inches of soil to the base of my Aspen trees (out to about 5 feet before reaching the old soil level).  They were there when we moved in 8 years ago and were quite large then.  I told them not to do it, for I thought it would kill the trees -- they weren't sure.   Will doing so kill the trees?  D. D., Colorado Springs, 2/14/04
   It is very likely that adding 12 inches of soil to the base of the aspen trees would kill them.  You were wise to tell the workers not to do it.

Q:    I have a cabin on 40 acres 8 miles S.W. of Buena Vista at about 9000 feet.  I have some aspens nearby our cabin and I would like to do something to encourage them to multiply.  The 40 acres are 80% Ponderosa Pine, 18% Douglas Fir and only 2% Aspen.  The property is thick with trees.  B. K., Westminster, 1/24/04
A:    It is common for pine and fir trees to take over and push out short-lived aspen trees.  Aspens perform better when they get plenty of sunshine and water and aren't in a battle with competitor trees.  Therefore, you may want to clear away some of the pine and fir trees that are growing in the area where you would like more aspen trees to grow.  Aspens produce suckers that will provide additional mature trees eventually if growing conditions are good.  Fertilize the existing aspen trees in spring.

Q:    I live in Longmont, Colorado.  I have a patch of Aspen trees on both ends of my patio.  I have noticed in the last 2 years that after mid-summer thru fall it seems that a large number of yellow jackets are attracted to the leaves of the aspen trees.  There does not seem to be any sign of a nest, however, the yellow jackets can be a bit aggressive.  They appear at dawn and seem to be around the trees until sundown.  I do not notice the yellow jackets on any other foliage in the yard.  Is there something that can be done to deter the yellow jackets without endangering the birds that feed from feeders in the aspen trees?  S. B., Longmont, 8/10/03
A:    Yellow jackets often feed on insects that produce honeydew, such as aphid and scale.  Aspen trees are commonly infested with these pests.  Hosing off the trees with a strong jet of water may help get rid of the honeydew and pests that attract them.  You also might consider using yellow jacket traps that are available at garden centers.

Q:   Our aspen trees have corky lumps on the roots.  The lumps can be seen above the surface of the soil in our yard. What are these lumps?  W. C., Ft. Collins, 8/6/03
A:    The corky growths are probably Aspen Gall.  They are unsightly but should not kill the trees.  There are no remedies.  Try to keep the trees healthy by providing sufficient water, cleaning up fallen leaves in autumn and fertilizing the trees in spring as needed.  If the trees become heavily infected you may want to remove them.

Q:    I have several aspen clumps that are shooting off seedlings.  I've tried to transplant the seedlings, with no success.  Do you have any suggestions? S. H., Vernal, UT; 7/28/03
A:     There are a couple of methods you might try using to transplant aspen suckers/seedlings:
        1) Allow the shoots to get about eight to twelve inches tall.  Cut them off at ground level.  Dip the cut end in a powdered or liquid rooting hormone (available at garden centers).  Plant the cutting in a one gallon container filled with a mixture of equal parts perlite and vermiculite.  You can also use commercial potting soil made for planting seeds.  Make a small hole in the soil and place the cutting in the hole.  Press the soil firmly around the cutting.  Moisten the soil carefully.  Place a clear plastic bag over the top of the plant to maintain a humid environment.  Place the container in a spot that has bright light, but not direct sun.  Water regularly to keep the soil moist but not soggy.  Leave the cutting in the container several weeks until it has formed roots.  It can then be planted in the garden.  Be sure to add compost to the planting hole.
       2) To plant the aspen suckers, prepare planting holes by amending the soil with compost.  Dig up the suckers along with a good amount of soil around the roots.  Plant these in the prepared holes and water them immediately.  Keep the soil moist, but not soggy, while the shoots are taking root.  Place mulch around them to retain moisture.  Do not fertilize them at this time because fertilizer could burn the roots.
    Hopefully, you will have success with one of these methods.

Q:    I live in Boulder and recently cut down some Aspens that were diseased and causing problems with my plumbing pipes.  The roots are still sending up sprouts.  How do I get rid of the sprouts?  A. W., Boulder, 7/4/03
A:    You can get rid of the aspen sprouts by spraying them with Roundup.  Do not allow any spray to get on desired plants or lawn near the sprouts, as it kills everything.

Q:    Great site!  I recently bought a house in the Denver area, and a fair amount of the aspens in the front appear diseased.  They are forming what looks like bark (texture) and are no longer smooth and white.  One of them has a large cut and some sap coming out. 
   What kind of disease is this?  Any fix?  I'm ready to pull them out, but should I remove the entire grove out front?  The ones in the backyard (south facing) seem to be fine.  Thank you in advance!  C. B., Centennial, 4/23/03
A:    Aspen are prone to numerous problems.  Stress due to the drought has made them even more susceptible to disease.  Some possibilities for the symptoms you described include these.
       1) If the new bark being formed looks like marble-shaped knots on the branches it is poplar twig galls.  These will not harm the tree.
       2) If the bark on the trunk and branches has discolored areas or gouged, depressed areas the trees may be developing cankers.  Oozing of sap is common when cankers occur on aspen.  Fungicides offer some protection.
       3) The cut with sap coming out may be due to freeze damage.  The wound should gradually heal.
       4) Rough bark of aspen is a disease that results in rough oval spots or corky ridges on the bark.  It is also caused by fungi but will not kill the trees.
       To prevent the spread of diseases to the healthy trees, you may want to remove the trees that are diseased.  Or, get rid of all of them at once to save time and trouble.  When replacing these trees I encourage you to select ones that are better suited to this area than aspens.  Aspen are beautiful trees, but they just have too many problems! 

Q:    I live in Buena Vista, CO.  We managed to purchase two 10-15' clumps of aspens (with root ball) rather inexpensively.  Please advise as to the planting and care of these aspens.  Our soil is rocky and dry.  Thanks for any help you may offer.  D., Buena Vista, 4/14/03
A:    When planting the aspen clumps, choose a site that receives sun at least half of the day, preferably more.  Dig a hole that is two or three times as wide as the root ball and the same depth as the root ball.  After placing the clump in the hole, fill the hole with a mixture made from compost (20% - 30%) and soil from the hole (70% - 80%).  Build up a wide well with soil around the tree and fill it with water.  Place a 3 - 4" deep layer of mulch around the base of the tree, keeping it a few inches away from the trunk.  Keep the trees moist but not wet while they become established.  Then gradually reduce watering.

Q:   My aspen tree is about two years old. It has been in the ground for three or four months. I regularly water it, yet the leaves are yellow and turning brown on the edges. Is this normal, or is there something I should do about it?  S., Leander, TX; 11/21/02
A:   The leaves of aspen trees normally turn yellow before dropping in fall.  If the leaves are yellowish and have dark green veins at other times of the year, the tree may be iron deficient, a condition called chlorosis.  You can apply chelated iron, available at garden centers, to correct this condition. 

Q:   I went to transplant some aspens in my yard and discovered the 2 trees I want to move are infested with what appear to be aphids.  I read through your Q & A comments looking for some advice, but thought I'd better share my problem first-hand.  I sprayed the aphids with insecticide, but I would like to ask, should I try to hose off the remaining bugs and eggs before winter fully sets in? And, then should I spray the trees with dormant spray?  Also, since the trees are under attack, should I wait until Spring to transplant them?  B. D., Boise, ID; 11/3/02
A:   If weather permits, hose off the remaining bugs and eggs.  Also, the trees should be sprayed with dormant oil in spring before they leaf out.  It is a
bit late to transplant the trees.  You should plant them in March or April once the ground is no longer frozen.  This will allow the roots to become
somewhat established before hot weather arrives in summer.  Aspen trees are beautiful, but unfortunately tend to have a lot of problems.  Good luck with
your efforts to keep them healthy.

Q:   Do all aspen trees lose their lower leaves when they mature?  I have recently moved to the mountains and want to shade a couple of low windows.  I'm wondering if I plant an aspen tree that is not crowded by other tall trees whether it would keep its lower leaves forever (or for a long time).  J. Y., Edward, 6/20/02
A: Aspen trees planted in urban/suburban landscapes that aren't overshadowed by a forest canopy do not lose their lower leaves like the ones you see in the mountain forests. 

Q: Greetings from Western Washington!  Since I brought Aspen saplings back with me from CO several years ago (about 1 1/2'high then), I figured you are probably better able to answer my questions about these wonderful trees than the local nursery.  I have 3 planted in my backyard and they have done quite nicely (over 10' tall now), I am pleased to say.  However, I have found that they need a little taming, some gentle pruning of the lower branches, but want to do it at the proper time.  I have coddled these youngsters since "infancy" so am a bit like an overprotective parent when it comes to caring for them.  If you could advise me as to the best time of the year to do this pruning, I would be most grateful.  The local nursery told me fall is best.  What do you recommend?  Thanks in advance!  S. S., Marysville, WA; 6/5/02
A:   A good time to prune aspen trees is in early spring just prior to when the trees leaf out.  Aspen are very susceptible to many diseases and pests that can enter the tree through the pruning cut wound.  Because these diseases and pests are less prevalent in cold weather, it is a good time to prune.  The pruning cut wound will callous over, or "heal," when the tree goes into its growing spurt in spring.

Q:   I just bought a house that has 15 to 17 aspens in the back yard.  The root system spans the entire yard and suckers are popping up everywhere!  Is there any way to stop them?  What should I do with them, just pull them out? K. F., Colorado Springs, 5/27/02
A:   There is little you can do to prevent suckers.  You should snap or cut them off as soon as they appear.  Do not spray them with Roundup or any other herbicide.  These products will travel through the root system back to the parent tree and damage it.

Q:   I have two Aspens in my backyard and noticed one of them has a branch coming off of the main trunk that has many white round spots all over. The white spots do not appear any where else on the tree. There are no white spots on my other Aspen. Both were planted together. There are far less leaves on the affected tree than on the other.  I live outside of Chicago. The weather so far has been wet and cold. What should I do?  5/21/02
A:   The aspen tree may have scale, possibly Scurfy Scale.  One method of managing scale infestation is to prune off heavily infested branches.  Insecticide sprays are effective only when eggs have just hatched and the young crawlers don't have a protective covering yet.  Next spring you may want to use a dormant oil spray before leaves emerge to kill over-wintering eggs.

Q:   I live in Steamboat Springs.  I have quite a lot of aspen trees in my backyard and the adjacent green belt.  I had a "tree expert" out spraying my pines for pine beetles and he checked out my aspen trees while there.  He said quite a few are dying and probably need to be cut down.  Some of the trees are leaking a sort of sap out the sides and others have a lot of dead branches and a soot like powder on them.  He also suggested that he could put a plug in some with some sort of medicine.  He said aspens are very sensitive and will get bugs with just one little scratch in them. How can that be?  I hate to lose any of my trees.  Some of them are quite mature.  Do you have any suggestions?  Should I get a second opinion?  J. M., Steamboat Springs, 5/16/02
A:   Unfortunately, aspen trees are very short-lived and highly prone to insects and diseases.  I suspect the information the tree expert gave you is correct.  I do recommend, however, that you get a second opinion from an arborist about treatment options.  You may also want to get a few bids on this task.  Good luck.

Q:   Hi!  I have concerns about an aspen grove in my friend's back yard.  They live in the foothills by Denver on a natural wooded lot.  Last year the trees had problems with black aphids and of course lots of sooty mold.  In the fall the leaves did not turn the gold color and dropped early.  What can I do to improve the grove?  Would hort. oil help at all or any other cultural practices?  Thank you.  L. G., Lakewood, 2/18/02
A:    Horticultural oil may be helpful for treating the aspen trees because it will kill any aphid eggs that have over-wintered on the trees, as well as killing other possible pests such as scale.  Because it smothers pests, it has fewer negative side effects on the environment than other types of insecticides that poison.  If possible, dead leaves should be raked up since they may harbor disease organisms and pests.  If aphid infestation is severe again this summer there are insecticides that can be used at that time.

Q:    I live in Bailey, CO at 8800 feet elevation. We have a grove of Aspen that was badly infected with aphids last summer. I'm wondering if the weather is cold enough this winter, will that kill off the overwintering eggs?  If so, how cold and for how long does it need to get?
Thanks for your time.  D. V. D., Bailey, 1/20/02
A:    I wasn't able to find any information concerning how cold it needs to get to kill over-wintering aphid eggs.  Because aspens normally grow in mountainous areas, the type of aphids that attack aspen trees are probably well-adapted to cold weather.  If the problem was severe last year you may want to consider spraying the trees in March with a dormant oil.  This method of control has advantages over spraying with an insecticide later in the year when the trees are in leaf.  Some insecticides would discolor the leaves and would be toxic to beneficial insects that prey on pests.

Q:   I am having trouble with the Aspen trees in my front yard.  When the trees bud in the Spring they look healthy, then they start to turn light green and eventually yellow (like fall of the year).  Then black/brown spots appear.  When this was first noticed, I consulted a nursery and started to spray HALTZ every 10 days.  I raked up the leaves in the fall, and this year the same thing happened.  Any suggestions on how to save this tree? D. D., Colorado Springs, 10/2/01
A:   Aspen trees are notorious for problems like the ones you described.  Yellow leaves with green veins may indicate iron chlorosis, which can be corrected with chelated iron.  The black/brown spots are signs of a fungal leaf disease such as Ink Spot or Marssonina Blight, which can be treated with a fungicide. The fungicide must be applied at bud break when leaves first emerge in spring and repeated two or three times at intervals of 12 to 14 days.  The fungicide is not effective if applied after leaves are infected.  Continue to rake up all leaves in the fall and dispose of them.  Spores that cause leaf disease over-winter in fallen leaves and other debris.  Keep leaves dry when watering by using a drip system rather than sprinklers that spray the leaves.  Water in the morning so leaves can dry out in the sun.

Q:   Hello.
  I live in northern West Virginia.
  Will Aspen trees grow in my area?  D. W., Fairmont, W. V.; 7/25/01
A:   If you live in an area with climate and soil conditions similar to those of Colorado's mountainous areas, you may be able to grow aspen -- or at least a relative of this beautiful tree.  Quaking aspen (Populus tremuloides) is a member of the Poplar family.  A similar tree is European aspen (Populus tremula 'Erecta'.

Q:    I live in Carbondale, elevation 6000 ' plus.  Have many healthy clumps (two to five about 2 to 4 inch trunks) of Aspen planted (by previous owner) about two years ago.  This week, one by one on separate days, three clumps are showing curling leaves.  The leaves are curling toward the underside of each leaf, leaves show no insect holes and have remained dark green.  I have turned off the watering but would love your suggestions. J. S., Carbondale, 5/26/01
A:    Curling leaves often are a sign of aphids.  Aphids suck the sap from plants, so you won't see chewed holes.  There are several steps you can take to manage them.  Hoses the trees off with a strong jet of water, spray them with an insecticidal soap, use an insecticide if infestation is severe, or apply dormant oils in the winter.

Q:    I live in Loveland, CO, and have several Aspen trees with stems and limbs that have 1-2 inch round looking formations.  The formations protrude on many branches.  Have you seen this before?  Is there a treatment?  D. M., Loveland, 4/17/01
A:    The formations you described are very common on aspen trees.  They are called poplar twiggalls.  They are created when the poplar twiggall fly inserts eggs in developing stems.  Larvae hatch and feed within the stem, causing the swollen gall.  Fortunately, these galls do not threaten the health of the tree. There are no effective chemical controls to prevent galls, although predators such as birds and parasitic wasps are good natural controls.

Q:    I am trying to locate aspen trees for planting at our farm in N E New York State.  Can you help?  M. M., Patterson, N. Y.; 10/23/00 
A:    Aspen trees may be available in your area at larger nurseries and tree farms. Ask for them by their botanical name, Populus tremuloides. If they are unavailable, you might try to find Populus tremula 'Erecta', a European aspen that is upright, narrower, and more adaptable. I'll see if I can find any mail order sources.

Q:    Why do the Aspen trees in Denver tend to look shabby?  Is this a bad tree to consider?  A. L. , Denver, 10/23/00 
A:    Aspen trees are definitely a poor choice for Front Range landscapes. The trees become stressed due to the soil and climate, and therefore become susceptible to disease. They perform best in the mountains. 

Q:    We have an aspen tree that is several years old.  The tree now has a bald spot in the middle.  There is foliage on the bottom and also the top of the tree.  Recently, several of the individual branches have dying leaves on the end of the branches.  Do we need to cut the dead parts out?  Will we lose the whole tree?  P. B., Golden, 8/9/00
   Your description of dying leaves on the ends of several branches leads me to suspect that your aspen tree has leaf and shoot blight.  Leaves develop brown or black splotches, become distorted and dry out.  The disease also infects the shoots.  Stems blacken and the tips of the stems curl like a shepherd's crook.  Damage begins at the tips and progresses downward through the branches.
   The fungus that causes leaf and shoot blight over-winters in infected stems.  Therefore, you should prune off infected shoots.  Be sure to disinfect the pruners with Lysol, alcohol or diluted bleach after each cut to prevent spreading the disease.  Also, you should rake up fallen leaves and stems.  Next spring spray the tree with a fungicide to prevent re-infection by airborne or over-wintering spores.  
   You should inspect the tree for cankers.  They will look like wounds or gouges in the trunk or branches.  Trees damaged by cankers may have yellowish or orange branches that have no leaves.  Prune off these bald branches, being sure to disinfect the pruners between cuts.
   I hope you won't lose the tree too soon.  Unfortunately, aspen tend to be short-lived at lower altitudes.

Q:    I planted an aspen tree in May this year.  It now has developed brown spots on the leaves.  What is causing this?  It is planted in a lawn that is healthy.  I also have other aspens planted this year and they are ok.  C. A., 8/7/00
   Aspen trees planted on the Front Range are very susceptible to disease.  One of the most common diseases is leaf spot, especially Marssonina leaf spot.  Leaves develop dark brown or black round spots that may have white centers and a yellowish halo.  Usually, leaf spot is most evident during July and August.  The fungus that causes this leaf disease is spread by windblown spores.
   Unfortunately, it's too late to spray trees after symptoms appear.  Fungicide sprays can prevent leaf spot to some extent, but they can't cure infected leaves.  The time to spray is in spring when trees begin to leaf out.
   The fungus Marssonina survives winter on infected fallen leaves.  Therefore, it is very important to rake up fallen leaves in the autumn.  Also, keep trees dry by using drip irrigation or running sprinklers early in the morning so leaves can dry off right away in the sun.  Healthy trees are more resistant to disease.  Be sure to provide adequate water and fertilizer.  You may want to use a fertilizer that contains chelated iron, since aspen trees are prone to iron deficiency.  For additional information contact your county Colorado State University Cooperative Extension office and ask for Factsheet 2.920.

Q:    I have been visiting Colorado from the UK for a number of years now on vacation and have admired those beautiful aspen trees.  We have a reasonable sized garden here where I live and are currently doing some alterations and as such wonder if aspen trees would grow here in the UK?  K.S., United Kingdom, 8/6/00  
  The botanical name for aspen trees is "Populus tremuloides."  Aspens grow well at elevations of 7000 feet above sea level and higher.  They prefer moist, acidic soil that drains well.  Plant trees in a sunny location on the north or east side of buildings.  Aspens perform best in areas that have warm summers and cold winters ( no colder than -40 degrees F). 
   Members of the "Populus" family can be a problem.  They have invasive roots that damage pavement, sewer lines, and septic tanks.  They form suckers, sending up new shoots from their roots in lawns and flower beds.  Aspen trees that are grown at low elevations are prone to insects and diseases such as leaf spot and canker. 
   John Cretti, a popular garden expert in Colorado, suggest that homeowners consider using "Populus tremula 'Erecta,' " a European aspen that is less likely to sucker or develop problems.  We wish you luck in finding a tree similar to the aspens in Colorado that will work well in your yard.