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The Master Gardeners: Your winter watering warning

February 12, 2017 GMT

Despite occasional rain and snowstorms, Santa Fe winters have become increasingly warmer and drier. A winter of sunny, dry days means your trees, shrubs and perennials need supplemental moisture to survive and thrive.

According to the Colorado State University Extension Fact Sheet 7.211, “The result of long, dry periods during fall and winter is injury or death to parts of plant root systems.”

Without a strong root system, plants become weaker and more susceptible to disease and damage during the subsequent windy springs and hot summers.

Winter watering is no one’s favorite chore, but if you do not want to lose those evergreens, deciduous trees, shrubs, roses, and perennials that you planted and cherish, you need to water them on a regular basis throughout the winter months.

Do not be deceived by snow! It takes a foot of snow to equal one inch of rain. A dusting of snow looks lovely but will not do your watering job for you. Evergreens (including pines, spruces, junipers, firs, arborvitae, yews, euonymus and pyracantha) continue to transpire moisture through the winter, making them particularly vulnerable to drought stress during dry winters. Deciduous trees, woody shrubs, roses and perennials also require supplemental watering. Water all your plantings except desert succulents, agaves and yuccas, bear grass and cactus. Winter watering of those could rot their roots.

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Winter watering takes time as it requires a long, deep soaking to get the area around the roots really wet. Because trees and shrubs have most of their roots in the top 18 inches of soil, you need to moisten the top foot (yes, 12 inches!) of soil in the root zone every time you water. Watering in the middle of a warm day allows the water to soak down to the roots more easily. Depending on the amount of precipitation we receive, you will probably need to water once or twice per month.

Pay attention to the soils and microclimates in your garden as you plan your watering. Plants in sandy soil or in sunny, windy or exposed areas — especially those on south- and west-facing slopes — need more water than those in heavy clay soil or on the north or shady sides of your property. Plants getting reflected heat from buildings, walls and fences also dry out much faster. Recently planted evergreens and shrubs are the most susceptible to winter drought.

The Colorado State University Extension fact sheet states that that until a newly planted tree is established (one year per inch of trunk size) it needs 10 gallons of water for each diameter inch of its trunk measured at knee height. For example, a 2-inch diameter tree needs 20 gallons per watering. Newly planted shrubs need 5 gallons two times per month. Established shrubs, less than 3 feet tall, need 5 gallons monthly, while shrubs more than 6 feet require 18 gallons monthly.

Mulching is also very important to help trees and plants retain their moisture. Apply mulch to a depth of 4 inches, allowing 6 inches of space between the mulch and tree trunk. However, when you water, be careful to get moisture under the mulch so that the mulch does not absorb the water before it gets down to the roots.

Think about your garden now. Are you doing enough winter watering?

Catherine Lewis has gardened in Santa Fe for many years and has learned these winter watering lessons the hard way.