Winter watering is a task that most people do not look forward to. That’s because we all will need to drag out those stored hoses and watering cans rather than rely on any installed irrigation systems. Of course I am assuming you “blew out” your irrigation system and that you stored your hoses in a place out of the weather. I finished my last watering just the other day and coiled up my hoses in a trash can in the garage.
Winter is a challenging time to water because of shorter days, colder air and soil temperatures and hence a limited time to actually water. But just because your deciduous trees no longer have functioning leaves doesn’t mean they don’t need a watering or two. And this is especially true of evergreens that continue to transpire water out of their needles and leaves.
Dry air, low rainfall, little soil moisture and fluctuating temperatures are characteristics of fall and winter in our area. Often there is little or no snow cover to provide soil moisture from October through March. Trees, shrubs, perennials and lawns under these conditions may be damaged if they do not receive occasional drinks during the winter. I don’t know about you but I generally get only two to three inches of rain during the six months of fall and winter. And snow can be an iffy thing the lower in elevation you go into the valley.
Snow can be a great insulator, both from temperature fluctuations and in retaining existing soil moisture. But most areas in Delta County do not get long lasting snow cover. And the soil water value is somewhat limited since much snow moisture is lost to evaporation.
The result of our 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. But later in the spring or summer, plants weakened from too little water may die or leaf out erratically when temperatures rise. Weakened plants also may be subject to more insect and disease problems.
Woody plants with shallow root systems are especially vulnerable to fall and winter dry periods. These include European white and paper birches; Norway, silver, red, Rocky Mountain and hybrid maples; lindens, alders, hornbeams, dogwoods, willows, and mountain ashes. Evergreen plants that benefit the most from off season watering include spruce, fir, arborvitae, yew, Oregon grape-holly, and boxwood. Pines and curlleaf mountain mahogany are less susceptible to winter desiccation but still should be watered. Woody plants also benefit from mulch to conserve soil moisture.
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. Lawns also are prone to winter damage. Newly established lawns, whether seeded or sodded, are especially vulnerable. Susceptibility increases for lawns with south or west exposures. Cool season grasses such as blue grass need supplemental winter watering but buffalograss does not.
I strongly recommend watering trees, shrubs, lawns, and perennials during prolonged dry fall and winter periods to prevent root damage that affects the health of the entire plant. I would water only when air and soil temperatures are above 40 degrees F with no snow cover. Established large trees have a root spread equal to or greater than the height of the tree. Therefore you should apply water to the most critical part of the root zone within the dripline. Apply water at mid-day so it will have time to soak in before possible freezing at night. A solid layer of persistent ice on lawns can cause suffocation or result in matting of the grass.
Plants receiving reflected heat from buildings, walls and fences are more subject to damage. The low angle of the winter sun makes this more likely on south or west exposures. Windy sites result in faster drying of sod and plants and require additional water.
How often to water is often a question I receive. The general advice is once a month for trees and woody shrubs. This may be sound advice for folks in the valleys but those of us living higher up can get away with less frequent waterings. For over ten years of living in Cedaredge I have gotten away with watering everything in November one last time and then again in February if needed. So get out those hoses and get to watering. Your plants will thank you.
Jim Leser retired to Cedaredge after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.