Frost, cloudy skies, and light snow give the impression that trees, shrubs, perennials, and lawns are getting plenty of water during the winter months. However, Colorado snow is usually dry and provides the equivalent of one inch of rainwater per every 12 inches of snow. This low moisture content combined with high winds and harsh, high altitude, low UV sunlight leaves landscapes open to a type of injury known as “winter drought.” To ensure healthy spring growth, supplement natural precipitation with monthly winter watering.
Only water when there is no snow cover and when temperatures are above 40 degrees. Water in mid-morning so that the moisture has time to soak in before temperatures dip below freezing. Deep, infrequent watering is more beneficial than shallow, frequent watering. You’ll only need to add supplemental water once or twice a month, depending on natural precipitation. You’ll have to drag out hoses, sprinklers, and drip hoses, since irrigation systems will be turned off for the winter, but the extra effort will yield amazing results.
Before watering, use a long screwdriver or knitting needle to test the soil for moisture. If you can easily insert it into the soil to a depth of 6-8 inches, don’t water. If you can’t, it’s time to supplement.
By the way, snow is an excellent soil insulator, so as you shovel decks and walkways, pile snow around trees, shrubs, and perennials that are susceptible to winter drought.
All trees benefit from additional water in winter, but newly transplanted trees and trees 3 years and younger are especially susceptible to winter drought injury. This is because they haven’t yet had time to establish a strong root system to maintain healthy growth. Trees with shallow roots systems, like spruce and fir, are also in danger. Winter drought injury isn’t noticeable until the following spring when the tree begins to leaf out with new growth. Leaves and blooms will appear normal at first as the tree lives off food reserves stored in its roots. However, once the reserves are depleted, the leaves soon die back, leaving homeowners puzzled. Depending on the extent of the damage, part or all of the tree will die off. Even if the tree survives, it will be open to disease and insect infestation.
For healthy growth in spring, trees need about 1 inch of water every three weeks during winter. Take into account the amount of snow we’ve received for the month, then supplement accordingly. If the tree is newly planted/transplanted, water near the root ball, being careful to keep water away from the trunk. Only roots absorb water, and trunk bark can be damaged by frozen water. For established trees, water around the dripline. To find the dripline, imagine a line drawn across the top of your tree that reaches to the longest branches on both sides—sort of like a straight umbrella. Now imagine ropes hung on each end of the line that drop to the ground. If you could spin the top line all the way around, the ropes would inscribe a circle where the tree’s roots are located—that’s where the tree needs water. Remember to water slowly so that the moisture can sink in. Puddles will turn to ice that could injure the trunk of the tree.
Shrubs, Perennials, and Lawns
The screwdriver/knitting needle trick mentioned above is your best tool for determining when to water the rest of your landscape. During dry winter months, plan to water once or twice a month if there is no snow cover. Juniper, euonymus, and other shrubs with shallow roots systems need extra care. Water around the rootball as shrub roots don’t extend out like tree roots do. Lawns that are newly planted—whether seed or sod—will need supplemental water when there is no snow cover.
After watering, don’t forget to disconnect the hose from the spigot as it may freeze and cause damage to your home.
The extra work you put in by watering this winter will make your landscape dazzle next spring. You’ll protect your valuable investment and your healthy, lush landscape will be the envy of the neighborhood next season.