Dry air, low precipitation, little soil moisture and fluctuating temperatures are characteristics of fall and winter in many areas of Colorado. Trees, shrubs and perennials under these conditions may be damaged if they do not receive supplemental water.
The result of long, dry periods during fall and winter is injury or death to parts of plant root systems. Affected plants may appear perfectly normal and resume growth in the spring using stored food energy. Plants may be weakened and all or parts may die in late spring or summer when temperatures rise. Weakened plants also may be subject to insect and disease problems.
Here in Archuleta County, most of our trees are native to the area and are less sensitive to these dry conditions. Woody plants with shallow root systems, however, require watering during extended dry fall and winter periods. These include aspen and spruce, which prefer more moisture and could benefit from some supplemental watering. In addition, any herbaceous perennials and ground covers in exposed sites are more subject to winter freezing and thawing. This opens cracks in soil that expose roots to cold and drying. Winter watering combined with mulching can prevent this damage.
Trees, shrubs and perennials planted within the past three years are most susceptible to winter drought injury. Trees generally take a minimum of one year to establish for each inch of trunk diameter. For example, a 2-inch diameter tree takes a minimum of two years to establish under normal conditions. So, to be on the safe side, trees planted within the past three years should receive some additional moisture.
Trees obtain water best when it is allowed to soak into the soil slowly. Water only when air temperatures are above 40 degrees F, applying water at midday so it will have time to soak in before possible freezing at night. Apply water to many locations under the dripline and beyond if possible. As a general survival rule, apply 10 gallons of water for each diameter inch of the tree. For example, a 2-inch diameter tree needs 20 gallons per watering. Use a ruler to measure your tree’s diameter at 6 inches above the ground level. Remember to water slowly to allow the water to soak into the soil.
Newly planted shrubs require more water than established plants. The following recommendations assume shrubs are mulched to retain moisture. Apply 5 gallons two times per month for a newly planted shrub. Small established shrubs (less than 3 feet tall) should receive 5 gallons monthly. Large established shrubs (more than 6 feet) require 18 gallons on a monthly basis. Decrease amounts to account for precipitation. Water within the dripline of the shrub and around the base.
Herbaceous perennial establishment periods vary by plant. Winter watering is advisable for herbaceous plants that were planted during the past year and perennials located in windy or southwest exposures.
