One of the brightest spots of living on the Front Range of Colorado is its winters. With more than 300 days of sunshine annually, we seldom see extended periods of the grey, chilly, precipitating skies common in so much of the country. It’s not unusual for daily highs to make it above 50 degrees. Much of this we have our elevation and distance from an ocean to thank – our sunlight is more intense than at sea level and our humidity lower, resulting in greater warming during the day compared to regions of similar latitude to our east or near a coastline.
Unfortunately for many landscape plants, however, that same day-night temperature differential spells trouble when paired with our lack of soil-insulating snow cover. The resulting environment of warm days, frequent wind, and intense sun increases water demand, while low humidity saps the soil moisture reserves that our limited precipitation may provide. As a result, our landscape plants are predisposed to dehydration-induced stress and root damage, both of which are exacerbated by freezing temperatures. Thankfully, one of our simplest gardening tools makes one of the most effective management tools against winter desiccation in our gardens: winter watering with the good old-fashioned garden hose.
While hydrating the plant via winter watering is important, it’s only half the story, since winter watering also serves to displace air in the soil profile with water. Water makes a far better buffer against temperature fluctuations in soil pore spaces than does air, so hydrated soils experience significantly smaller and slower temperature fluctuations, further reducing opportunities for root stress. 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).
Until established, all woody plants (trees and shrubs) should be watered up to twice monthly in winter on days over 50 degrees. As a general rule, begin “winter” watering in November (fall by the calendar, I know) and continue through March during periods without snow cover and without significant precipitation. Speaking broadly, I assume one year of establishment for every inch diameter of a tree trunk, so a tree with a two-inch diameter trunk would require two years minimum to reach establishment after transplant.
Many established woody plants benefit from winter watering as well, though this may be less essential than for recent transplants. During periods without snow cover, I winter water established trees monthly in my garden and recently transplanted perennials and grasses somewhat less. 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 15 – 30 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.
Winter watering remains a cheap and effective tool in the gardener’s arsenal for staving off plant stress. Set a timer, set the hose, and tackle your Sunday chores, moving the hose every 30 or so minutes, and you’ll find it an easy task to knock out. Just don’t forget to unhook the hose from the spigot afterward!
Photo of Rock Garden: This snowless garden would be a good candidate for winter watering if it does not see mentionable snow cover or precipitation in the next two or three weeks.
Bryan Fischer is The Gardens' Curator of Plant Collections and Horticulturist. A version of this article was originally printed in North Forty News on Jan. 5, 2022.