by Bryan Fischer | Gardens on Spring Creek
Those of us who have spent a few years (or more) on the Front Range knows that winter here doesn’t look like winter in much of the country. As far as I’m concerned, this is a good thing; I don’t enjoy days of grey skies and persistent snow cover. Our woody landscape plants, however, would say otherwise.
Regular sunny days, wind, and a lack of snow cover combined with significant daytime warming even when nights are cold wreak havoc on many woody plants, especially those that are not yet established. Since cold and drought damage plant cells through similar mechanisms, both occurring simultaneously represents a double whammy for these plants. While we can’t control the temperatures our gardens may endure, we can control how much water ends up in them. At its most basic, this is the concept behind winter watering.
Typically, I begin winter watering in November and will continue until April during periods of dry weather and warm temperatures (think no snow cover and days breaking 50 degrees). Watering up to twice monthly for very sensitive species and plants that are not yet established is appropriate; once monthly suffices for most others as temperatures allow. One can quickly estimate whether a larger shrub or tree is established using the following formula regarding trunk diameter: for every inch diameter of a tree trunk, the plant will need one year in the ground to establish. So, a tree with a two-inch diameter trunk (measured six inches above the soil line) would require two years minimum to reach establishment after transplant.
As much as it hydrates the plant, winter watering serves to displace air in the soil profile with water. Water has one of the highest specific heat capacities of any liquid, meaning it can hold an enormous amount of heat energy compared to many natural substances. Slowly radiating this heat into the soil, water insulates roots and reduce temperature swings as well as hydrate the roots it envelops. This can have benefits beyond the roots, too, as there is some research to indicate that regular winter watering also reduces the likelihood of sunscald (also known as southwest injury) on tree trunks.
I’m of the mind that fewer moving parts leave less available to fail, so I water with a solid cast-iron sprinkler at the end of a garden hose, taking care to move the sprinkler every 30 or so minutes. Remember: the goal is not to deliver water to the tree as much as it is to hydrate the soil where roots may be, so wetting part of the root zone very well is less effective than wetting the majority of the root zone reasonably well. And, since the root system of a tree can extend up to three times its canopy width, ensure you water not only under the tree but around its perimeter, too.
The type of task that can be easily added to a day of work around the house, winter watering hardly feels like a strain when built into your regular routine as a monthly chore. Any day temperatures above 50F are a good candidate for winter watering – just be sure to water during the warmest part of the day and quit a couple of hours before dusk so water can make its way into the soil and off stems before freezing. Your landscape will certainly thank you and, hopefully, you’ll be able to enjoy those sunny Colorado days without the nagging concern that your landscape feels otherwise.