Gardening: Winter watering

As the weather begins to cool, many gardeners and homeowners anticipate shutting off of their automatic sprinkler systems. And for those who water “manually,” the end is in sight: no more standing around with the hose.

Truthfully, the end isn’t in sight, because to maintain tree, shrub, turf, berry and perennial health, it is necessary to water during the winter to mitigate our dry Colorado climate. This is particularly true for “warm” and dry winters, when we have less-than-normal snow. It’s a good practice to plan to water at least once a month from sprinkler shut-off until spring.

Prolonged periods of dry, windy weather without supplemental irrigation can cause root damage and affect the overall health of trees, shrubs, turf, berries and perennials. Although plants that suffer root damage may appear to grow normally the following spring, this is because they are using storage reserves of energy. Once the weather heats up during the summer, these weakened plants may die or be burdened with various insect and disease problems.

By Susan Perry
Colorado State University Extension Master Gardener in Larimer County

Root problems occur more often to woody plants that have shallow root systems, such as birches, maples, lindens, evergreens (spruce, fir, euonymous and junipers), and agastache. Even perennials and groundcovers can be affected by significant fluctuations between day and night temperatures, especially if they are in fully exposed locations, due to cracks in the soil that expose the roots. For landscape plants, a combination of good mulching and winter watering can prevent or significantl reduce damage. All lawns — new or established — can benefit from supplemental winter moisture. Areas that dry out the quickest are those with southern or western exposures.

New plants take several years to become established and should be watered during the winter according to this rule of thumb: water new plants at least twice a month and established plants at least once a month. Of all new plants in the landscape, trees are the most likely to suffer winter drought injury. Generally, it takes a tree one year to become established for each inch of trunk diameter. So, a new tree with a 2-inch trunk diameter will take at least two years to become established.

The time it takes perennials and shrubs to establish depends on a variety of factors. Container plants establish more quickly than bare-root stock, and those planted in the spring establish more quickly than those planted in the fall. When you consider the cost of new trees, shrubs, and perennials, it is advisable to be more cautious when determining a winter watering schedule.

To decide when to water, watch for extended periods (more than seven to 10 days) of warm (higher than 45 degrees), dry, windy weather where there is no snow cover on the ground. These are the conditions that are potentially most damaging to plants. When selecting a time to winter water, do so between 11 a.m. until 3 p.m. when temperatures are above 40 degrees. This allows the water to be absorbed before possibly freezing at night. Depending on the size of your yard, it may be necessary to water over several days to insure that all plants and lawn have been irrigated.

When winter watering, you can choose from a variety of methods: hand watering, deep-root needle, soaker hoses or hose-end sprinklers. Whichever method you choose, try to allow the water to soak slowly into the soil around the dripline and base of the plant. If you water trees with a deep-root needle, be sure to insert the needle no deeper than 8 inches and try to apply 10 gallons of water for each inch diameter of the tree trunk. Newly planted shrubs need five gallons of water twice a month, while established shrubs (under 3-feet tall) require five gallons per month to 18 gallons per month (shrubs taller than 6 feet). Turf, perennials and berry bushes will benefit from a good soaking at least once a month.

A combination of mulch in the fall and regular winter watering as needed per weather conditions will keep your landscape healthy and happy the following spring and summer.