Information for the Colorado Gardener


Aphids are common pests in Colorado gardens.  They transmit plant diseases, deform and curl leaves, and produce sticky honeydew that attracts ants.  Often, you can readily spot them clustered along stems, buds and leaves.  Many aphids are green, although they may be other colors such as pink or black.  Some have wings; some are wingless.

Fortunately, natural predators such as lacewings, ladybird beetles, syrphid flies, and other “good bugs” can control aphid populations.  A strong spray of water from the garden hose is often effective in removing them.  Insecticidal soap is also a popular remedy, and, when necessary, stronger chemical controls are available.


A plant that completes its life cycle within one year is called an annual.  A seed germinates and grows into a plant. The plant flowers, produces seeds, and dies all within the span of a growing season.  Some popular annuals are petunias, lobelia, marigolds and zinnias.

Aspen Trees         

The beauty of aspen trees has enticed many homeowners who live along Colorado’s Front Range to plant them in urban and suburban landscapes.  Alas, the growing conditions of these sites are far from ideal for this mountain native.  Aspen can be grown in urban/suburban areas, but they will be short-lived and have many problems. 

Aspen trees need acidic, light soil that drains well.  If you have heavy clay soil you should plant the trees on a berm (mound) of soil that has been well amended with organic matter.  Also, try to place the trees on the north or east side of the house where they will have some protection from intense heat and sunlight.

You should expect the trees to have problems with insects and diseases.  (You can find books about this topic!)  Some preventative measures to take are avoiding overhead watering, providing good air circulation by how you space the trees, and clearing away diseased leaves when they drop.  Also, dormant oils that help to control diseases are available. 


Deciduous shrubs and trees as well as some perennial flowers, fruits and vegetables that are sold with all the soil removed from their roots are referred to as bare-root.  These plants are sold while they are dormant in winter and early spring, often at a sizeable savings over plants in containers.  Select plants with healthy-looking, plump roots.  Before planting, soak the roots overnight in a bucket of water.  To plant, spread them out over a mound of soil in the planting hole.

Beneficial Insects     

Gardeners are gradually becoming aware that many insects and bugs do not harm gardens.  In fact, some insects and bugs benefit the garden by feeding on garden pests such as aphids and mites.  This group is known as “beneficial insects.”  Some well known beneficial insects are ladybird beetles (lady bugs), green lacewings, and syrphid flies.  Beneficial insects are present naturally in the garden.  You can purchase them by mail order or at garden centers, but keep in mind that when you release them, they may or may not stay in your yard.  Because insecticides kill both good bugs and bad bugs you should use chemical controls only when absolutely necessary.


Bracts are modified leaves.  They are quite colorful on poinsettias, dogwoods, bougainvilleas and other plants and are often called “flowers.”

Cool-season Grasses         

Cool-season grasses grow vigorously in periods of cooler temperatures such as fall and spring.  Generally, they tolerate cold winters well.  Growth slows down during hot summer months.  Some cool-season grasses are Kentucky bluegrass, perennial ryegrass and tall fescue.

Core Aeration         

Core aeration, also know as core cultivation, is a process that removes 2-3 inch long plugs of soil and thatch from the lawn.  It benefits the lawn by reducing soil compaction, controlling thatch build-up, and improving water and air penetration.  Spring and fall are the best times of the year to core aerate your lawn.  It is good to let the plugs disintegrate on the lawn so the nutrients can enrich the soil.


The crown of a plant is the point where the roots and the upper portion of the plant meet.


Disbudding is a technique that gardeners use to promote the production of large-sized flowers.  Some plants, such as chrysanthemums, tend to produce many small-sized buds that are forced to compete for food, light and space.  As a result, these buds develop into small-sized flowers.  When gardeners remove some of the buds (disbud), the remaining buds have the food, light and space they need to become large-sized flowers.


A plant that is in a stage during which it does not actively grow is said to be dormant.


To keep plants blooming as long as possible deadhead (pinch or cut off) old blossoms before they form seeds.  The plants, in an ongoing effort to produce seeds, will continue to produce flowers.

Harden Off         

Seedlings of annual and perennial flowers need to adjust gradually to the outdoor site where they will be planted.   Young plants are not used to bright sunlight and varying temperatures because they are started inside in a greenhouse. To help them make the transition to life outdoors, you should harden them off.  Set them outdoors for several hours in direct sunlight each day for a week, gradually increasing the amount of time they spend outdoors.  After hardening off they are ready for planting.


         Hardiness refers to a plant’s ability to tolerate frost and cold temperatures.

Integrated Pest Management (IPM)        

Informed gardeners realize that totally wiping out all insects in the garden is both unwise and unfeasible.  Pest management, rather than complete eradication of pests, is the goal.  An integrated approach that utilizes a combination of methods to keep pests in check is employed.  These techniques include

1)  Cultural controls: the use of gardening practices that promote healthy plants, such as crop rotation, proper fertilization and watering, good garden clean-up, etc.   

2)  Mechanical controls: the use of barriers, traps, handpicking of pest, etc.

3)  Biological controls: the use of natural predators (beneficial insects) such as ladybugs and green lacewings

4)  Chemical controls (the last resort):  the use of pesticides derived from natural sources and, when necessary, synthetic sources.

The use of IPM diminishes the need for chemicals and results in gardens that are safer for everyone—children, pets, birds, butterflies, and gardeners!

Lawn Fertilization        

There are three primary nutrient elements that plants need:  nitrogen (N), phosphorus (P), and potassium (K).  A “complete,” or “balanced,” fertilizer contains all three elements.  When you look at bags or containers of fertilizer you usually will see the percentage of each element listed as a number.  For example, if a 20-pound package of fertilizer has the numbers 15-10-5, the package of fertilizer contains 15 percent nitrogen, 10 percent phosphate (phosphorus), and 5 percent potash (potassium).  That is, it has three pounds of nitrogen:  20 lbs. x 15% (.15) = 3 pounds.  It has two pounds of phosphate:  20 lbs. x 10% (.10) = 2 pounds.  It has one pound of potash:  20 lbs. x 5% (.05) = 1 pound.

 If you want to apply this fertilizer at the recommended rate of one pound of nitrogen per 1000 square feet of Kentucky bluegrass lawn, you would use 1/3 bag of fertilizer per 1000 square feet of lawn.     

Lawn Mowing Guidelines         

Mowing height:  The recommended height for all types of lawns in Colorado is about 2 1/2 to 3 inches, with 2 inches the minimum height.  Grass that is cut shorter than this is likely to have more problems with disease, insects and weeds.  It is also more likely to be stressed by drought and heat. 

Frequency:  How often you need to mow the lawn depends on the lawn’s rate of growth.  In other words, it varies.  No more than 1/3 of the grass blade’s height should be cut off when it is mowed.  When grass is growing rapidly you will need to mow the lawn more frequently than during times of slow growth.  Mowing once a week on Saturday may be a convenient routine, but it isn’t what’s best for the lawn.

Grass clippings:  Don’t collect grass clippings—unless you want them for your compost pile.  Instead, allow them to drop back on the lawn.  The nitrogen and other nutrients in the clippings will enrich the soil.  Decomposition will not be a problem if you follow the guidelines regarding the frequency of lawn mowing.

Mountain Pine Beetle    

Outbreaks of Mountain Pine Beetles (MPB) have been responsible for the death of millions of trees in Colorado’s forest and yards.  Ponderosa, lodgepole, Scotch and limber pine are common targets.  Trees that are under stress due to overcrowding, old age, disease, or injury are especially susceptible to attack.  Unfortunately, little can be done to save infested trees.  Therefore, preventive action to control the spread of MPB is important.  Homeowners may want to spray prized trees in their landscape.  Infested trees must be disposed of properly to prevent the spread of this pest. The Colorado State Forest Service and Colorado State University Cooperative Extension can provide information and advice concerning MPB.


There are two basic kinds of mulches:  organic and inorganic.  Each has advantages and disadvantages.

Inorganic mulches, such as gravel and rock, don’t blow away in Colorado’s frequent windstorms.  Unlike organic mulches that decompose and have to be replenished, inorganic mulches do not require replacement.  Rock and gravel retain heat, which may or may not be an asset in certain circumstances.  A major advantage of inorganic mulches is that weed problems are largely eliminated when they are used over weed barrier fabric.  (Note: The use of plastic as a weed barrier is not recommended because it prevents water and air from penetrating the soil.)

Organic mulches include wood/bark chips, shredded bark, pole peelings, straw, grass clippings and pine needles.  Like inorganic mulches, these mulches limit weeds, reduce water evaporation, minimize soil crusting, help maintain an even soil temperature and prevent frost heave.  An additional benefit of organic mulches is that they improve the soil when they decompose.  However, because organic mulches use up nitrogen when they decompose, you should watch for yellowing of leaves, one of the signs of nitrogen deficiency.  Apply a complete fertilizer at the rate of two pounds per 1000 square feet.  (A complete fertilizer contains nitrogen, phosphate and potash.)

You can mulch beds and borders anytime if the mulch is being used to control weeds, maintain soil temperature or improve appearance.  When mulch is used to prevent frost heave, apply it after the ground has frozen.  A layer 3 to 4 inches deep is recommended.  Avoid piling mulch against tree trunks and at the base of shrubs as this can lead to problems with insects and disease.

Organic Matter         

Material that originates from a living organism (plant or animal) is called organic matter.  Examples include manure, compost (commercial or “homemade”), peat moss, ground bark, leaf mold, sawdust, straw and pine needles.


Plants that live from year to year and do not have woody stems are called herbaceous perennials.  Typically, these plants die down during the winter months and then grow back in the spring; therefore, you don’t have to replant them each year as with annuals.  Because perennials live in the same spot for several years it is especially important to prepare the soil well prior to planting.  Common perennials include columbine, penstemon, purple coneflower and pincushion flower.


A plant becomes root-bound when it is in a container too long.  When the growing roots have no place to go, they become matted and intertwined at the bottom of the container and begin to encircle the plant.  Eventually, the plant’s vigor declines and the plant may even die.



A plant’s roots and the soil they are growing in form the plant’s root-ball.


Root Zone                     

A plant’s root zone is the area throughout which the plant’s roots extend.


Rooting Hormone           

Rooting hormones are chemicals that stimulate the growth of roots on cuttings.  They come in both powder and liquid forms.


Soil Amendments            

Soil amendments are organic and/or inorganic materials that are worked into the soil to improve its texture, or tilth, thereby promoting root growth.  Examples of organic matter include compost, peat moss and aged barnyard manure.  Examples of inorganic materials are perlite, coarse sand, and gypsum.  Generally, soil amendments do not act as fertilizers because they contain limited plant nutrients.  Some common amendments, such as lime, are not suited to Colorado’s soils.  Others, such as gypsum and sand, are useful only in special circumstances and if used inappropriately, can worsen soil conditions.

Spider Mites         

Spider mites are a common pest in Colorado.  Because they are smaller than a pinhead and feed on the underside of leaves, gardeners often aren’t aware of their presence. Webbing on plants and yellowed, bronze-colored, stippled or deformed leaves are symptoms of infestation.  Leaves, stems and buds tend to dry out and turn brown.  Outbreaks occur primarily during hot, dry weather and are more prevalent on plants that aren’t well watered.  To prevent problems with mites, provide adequate water for plants and hose plants off periodically.  You can treat infestations with insecticidal soap or, if necessary, with miticides that are available for use on some plants.  Avoid the use of insecticides – many don’t kill spider mites.  Instead, they kill off natural predators of mites, resulting in even greater populations of this pest!


Sudden fluctuations of temperature and water loss during winter can damage the bark of young, thin-barked trees by killing new tissue.  Sunscald injury usually appears on the southwest side of trees.  Damaged bark changes color, becoming reddish, orange or yellow.  It cracks and sheds off, making the trunk highly susceptible to insects and diseases, such as borers and canker.  This can lead to the death of the tree.  Young honeylocust, birch, maple, crabapple and other thin-barked trees can be protected from sunscald by providing adequate water during winter and using tree wrap for the first two or three years after trees are planted. 



Thatch is a spongy layer of living and dead grass roots and stems that builds up between the soil and grass.  Kentucky bluegrass is prone to accumulating thatch, while buffalo grass and tall fescue seldom have it.  Once the thatch layer has become fairly thick, the grass will take root in it rather than in the soil.  This leads to problems because the roots are unable to absorb water and nutrients properly from the soil.  If the thatch layer is greater than 1/2 inch, steps should be taken to remedy the situation.  See Core Aeration.

Tomato Terminology                   

Determinate: This type of tomato produces only one crop that comes in over a period of a week to ten days.

Indeterminate:  This type of tomato produces tomatoes throughout the growing season, right up until frost.  These vigorous plants require cages or stakes.

V/F/T/N:  These initials on tomato plant labels indicate that a plant is a hybrid that has bred-in resistance to a specific tomato disease or pest.   V – Verticillium wilt, F – Fusarium wilt, T – Tobacco mosaic, N – Nematodes.

Tree Wrap               

Commercial tree wrap is a roll of corrugated paper that is used for wrapping the trunks of young trees to prevent sunscald.  Trees should be wrapped in October or November.  Start at the bottom of the tree and wind your way up the trunk.  Secure the top and bottom with stretchable tape.  Do not use string or other materials that could bind or cut into the trunk of the tree as is grows.  Be sure to remove the tree wrap in April.  Leaving the tree wrap on during summer restricts growth and the wrap can house insects and disease.

Warm-season Grasses        

Warm season grasses thrive in the hot weather of summer but go dormant and turn brown in cool or cold weather.  Some warm-season grasses are Buffalo grass, Blue Grama and Bermuda grass.


Whiteflies are common pests on houseplants.  During the summer they can become pests in the garden outside as well.  Whiteflies weaken and stunt the growth of plants by sucking out the sap.  Leaves become stippled, turn yellow, and drop off.  Yellow or white sticky traps, such as Tanglefoot and Tack-trap, can be used to control whiteflies.  Also, you can hose off plants with insecticidal soap or use products containing neem or pyrethrum.  Fortunately, whiteflies cannot over-winter outdoors in Colorado because freezing temperatures kill them. Therefore, in many situations outdoors, chemical control may not be warranted.

Winter Watering        

Unfortunately, Colorado’s winters are too cold to leave the automatic sprinkler system on, but too dry for lawns and many trees and shrubs.  Without sufficient water, plants will die or be damaged.  Therefore, it is necessary to continue watering after your sprinkler system has been winterized in the fall.  If there is no rain or snow cover for four to six weeks you should water.  Water in the morning on days when the temperature is above freezing and when the ground isn’t frozen so the water will be absorbed.  Use a lawn sprinkler to water lawns and established trees.  A soil-needle attachment on the hose works well for watering shrubs.


Winterizer Fertilizer    

Fertilizing lawns in the fall is a highly recommended lawn care practice.   Winterizer fertilizers are used in the fall (late-season) because they provide a number of benefits to lawns:  better fall and winter color, earlier green-up of the lawn in spring, better root growth, and increased grass density.  To be effective, the fertilizer should be applied when the soil is moist, while the lawn is still green and before the ground freezes.  Winterizer fertilizer may be applied to Kentucky bluegrass, ryegrass and tall fescue lawns at a rate of one pound of nitrogen per 1000 square feet of lawn during October or early November.  Do not fertilize Buffalograss, Blue Grama or Bermuda grass in the fall.