Winter Watering in Western Colorado

Curtis E. Swift, Ph.D.
Colorado State University Extension
Tri River Area

Introduction

Newcomers to Western Colorado are often amazed to hear of the need to water outdoor gardens and lawn areas during the winter. Except for the mountains, much of Western Colorado is free of snow and relatively dry during the winter months. Gardens and lawn areas may be moist in the upper one to two inches, but dry deeper in the soil. Neglecting to water during the winter often results in the decline and die-back of trees and shrubs the following July and August.

Winter Mites>

Lawn areas that do not receive water during the winter are more likely to be damaged or killed by winter mites. Winter mite injury is always much more severe on lawn areas with a southern or western exposure. Slopes and berms with a southern or western exposure are highly susceptible to this damage.

Woody Plants and Dehydration

The temperate zone species of trees and shrubs used in Western Colorado landscapes are quite resistant to cold. Once acclimated these plants are capable of withstanding -40 degrees Fahrenheit (-40 C) without much problem. Cool temperatures in the fall slow all aspects of plant metabolism and trigger changes that result in winter acclimation and maximum hardiness for the species.

The changes that take place in our temperate zone plants are somewhat affected by how the plant is cared for during the fall months. For example, water and fertilizer applied in September and October may result in continued growth and slow this process of winter acclimation (hardening off). Even when water and fertilizer has been applied around a woody plant, the first frost will normally trigger the acclimation process. Fertilizing lawn areas after October 15, as recommended with the Late Season Fertilization Program, avoids this problem since trees and shrubs will already by hardened off by that time.

The changes that occurs with some of our temperate zone woody plants as they acclimate for winter, may result in a hardiness much lower than - 40 degrees Fahrenheit. Why then do we hear people talking about winter kill of plants as if it were due to cold? Once temperate zone plants are hardened off, cold should not be an issue.

Winter kill of temperate zone woody plants is the result of dehydration of plant tissues, due to lack of water uptake from the soil and the drying effect of our bright intense winter sun (as happens with the canes of roses). As the soil dries, roots of these plants die and the plant is unable to replenish the moisture lost from its stems and branches. Some roses need additional protection to prevent winter dehydration.

Watering monthly during the winter should be done when air temperatures are above freezing and early enough in the day to allow the water to sink in by nightfall. If a coating of ice forms on the soil surface, root injury can occur due to a lack of oxygen reaching these living tissues. Even when the ground is frozen, water will sink in. A frog-eye, oscillating or other type of spray head sprinkler is recommended. A root feeder or soil needle it is very difficult to use during the winter months.

Placed on the Internet January 2, 1997
Updated May 31, 2009