By Dr. James Feucht, Colorado State University Cooperative Extension Landscape Plants Specialist
Colorado winters can be dry in more ways than one. During extended periods - particularly in January and February - when there may be little or no snow cover, the lack of soil moisture and atmospheric humidity can damage plant root systems unless they receive supplemental water.
Affected plants may appear normal and resume growth in the spring, only to weaken or die in late spring or early summer because the amount of new growth produced is greater than the weakened root system can support.
Most woody plants, which have shallow root systems, require supplemental watering during extended winter dry periods. Included are shade trees such as European white birch, Norway and soft (or silver) maples and lindens (basswood). Colorado spruce also is at risk.
Evergreen shrubs, particularly those growing near a house, may suffer root system damage during dry spells. Examples are plants such as Pfitzer and "Tammy" junipers.
Lawn grasses also are prone to winter damage. Newly established lawns, whether they are started with seed or sod, are especially susceptible to damage in dry weather. Pay particular attention to turf on south exposures.
Water during winter only when air temperature is above freezing. Apply water early in the day, so it will have time to soak in before nighttime freezing. If water stands around the base of a tree, it can freeze and damage the bark.
In most years, one or two winter waterings will be enough to keep plants from suffering winter damage.
A soil needle (root feeder) attachment to the garden hose is recommended for applying water to young or recently planted trees and shrubs. These attachments are available in garden supply stores.
When you use a soil needle, the depth at which water is applied will depend on the type of plant. For most junipers, about l8 inches is sufficient. With shallow-rooted trees, such as linden, maple and birch, 9-12 inches is correct. If a portion of a plant's root system is beneath a sidewalk or other obstructions, slant the soil needle to apply water beneath these surfaces.
When watering young trees, the most important area is halfway between the trunk and several feet beyond the "drip line" (the branch extremities).
If water is applied through a soil needle in a zigzag pattern around the tree, all parts of the tree will receive enough. Leave the needle in the ground for one minute per spot, moving it every six to eight inches.
For large, established trees, sprinklers are more efficient and the lawn can be watered at the same time.
For more information about winter watering and care of plants during winter, contact your local office of Colorado State University Cooperative Extension.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010