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Early spring is the trickiest time of all for Denver gardeners. Balmy days make us think it's tomato-planting time, then we're zapped by frosts--or blizzards!

Warning: Any plant that may be damaged by frost, for example, tomato, basil, or petunia, should not be planted until our average last frost date, between May 10 and 15.

All of our timing suggestions are rules-of-thumb. Our best advice is pay attention to the weather.


Typical Denver soil is heavy alkaline clay, although near creek and river beds, the soils are sandy. Adding organic matter improves both soil types. In clay, organic matter increases space between soil particles to improve drainage and aeration. In sandy soil, it helps hold the moisture and nutrients. The best organic amendments are relatively coarse: manure that has been aged over a year or partially decomposed compost. Rocky Mountain peat, gypsum, lime, wood ash, or sand should never be added to our soils.

Soil improvement is a continual process. Add a one- or two-inch layer of organic matter over the soil and then thoroughly mix it into a depth of about six inches. Holes for trees and shrubs should be refilled with a mixture of one-fourth organic matter with three-fourths soil from the hole.  CSU Fact sheet 7.222.

Soil is ready to work in the spring if it is thawed but not soggy. Resist any temptation to dig or plant in wet soil.

For more information see Soil


Pruning is a regular part of tree and shrub maintenance. Selective cutting of branches, stems, or twigs may improve the plant’s shape, bloom, strength, and health. Pruning should be done thoughtfully, one branch or stem at a time, rather than shearing or "topping off."

Dead, diseased, or injured plant parts can be removed at any time of the year. Plants that bloom on last season’s wood, including ornamental fruit trees and most spring- flowering shrubs, are pruned after blooming to maximize flowering. Those that flower on this season’s wood, usually summer- and fall-bloomers, are pruned while dormant in late winter or early spring. Most narrow-leaf evergreens may be pruned any time of the year, except in sub-zero weather.

Proper pruning of a deciduous shade tree maintains the tree’s appearance and allows air and sunlight to penetrate through the canopy. Main branches from the trunk should have wide angles of attachment with the trunk. They should be spaced fairly evenly from one another and be distributed around the trunk going up like spokes around an axle. Remove a branch that crosses or hangs directly over another. Trim out suckers that grow from the base of the tree and thin vertical shoots (water sprouts) from branches

To remove a large branch

Near the base of a branch is a swelling called a "collar." Cut just outside of the collar. Do not cut flush to the trunk or branch, nor leave a stub beyond the collar.

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Use a three-cut method to prevent stripping the bark. Make the first cut on the underside several inches outside the collar, cutting about half-way through. Make the second cut on the top of the branch an inch or so outside the undercut, cutting all the way through. Finish the job by cutting just outside the branch collar.

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CSU Fact sheets:

Pruning Fruit Trees 7.003

Pruning Deciduous Trees 7.207

Pruning Evergreens 7.205

Pruning Techniques for Shrubs 7.206

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Date last revised: 01/05/2010