Home & Garden: Watering lawns in winter
Free Press Gardening Columnist
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. The garden and lawn areas I have checked have been moist in the upper one to two inches, but dry deeper in the soil. Neglecting to water in early January and again in early February often results in the decline and die-back of trees and shrubs the following July and August. Lawn areas that do not receive water during the winter are more likely to be killed by the winter feeding activity of mites. This past spring many area lawns were damaged because of the insects. This winter mite problem is always much more severe on lawn areas with a southern or western exposure, especially on slopes and berms when winter watering has been neglected.
The temperate-zone species of trees and shrubs we use in our landscapes are quite resistant to cold. Once acclimated these plants are capable of withstanding 40 degrees below zero without much problem. Cool temperatures in the fall slow all aspects of plant metabolism and trigger the 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 a resulting resistance to harden off properly. 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 Oct. 15 avoids this problem since trees and shrubs are already hardened off by that time.
The super-cooling and other changes that occur with some of our temperate zone woody plants may result in a hardiness much lower than 40 degrees below zero. Why then do we hear people talking about winter kill of plants as if it was due to cold? Once temperate-zone plants are hardened off, cold should not be an issue.
Winter kill of these plants is the result of dehydration 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.
Watering 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 sprinklers are recommended.
A good soaking this month as well as in early February (unless we receive an unusual amount of moisture) will help prevent winter injury.
Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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