By Judy Kunz, Colorado Master Gardener
Picture in your mind a vast plain. No trees. Only miles of native grasses punctuated by scrub oak, other drought tolerant shrubs and a few native cottonwoods growing along the Platte River. That is what the Denver area looked like prior to the arrival of European settlers in the 1800s.
Situated on the leeward side of the Rockies and located on the western edge of the Central North American Steppe, Denver exists in a rain shadow. That means high and dry. Weather systems arriving here have, in many cases, precipitated out much of their moisture as they made their journey over the Continental Divide. Sometimes systems skirt to the north, both tracks leaving the Front Range area with only about 20 inches of moisture per year.
That isn’t enough precipitation to keep evergreens healthy. Because they don’t lose their foliage in the fall like deciduous trees, they tend to lose moisture through their needles because of desiccating winds and sunlight. In most cases, trees such as pine, spruce and fir in the landscape are dependent on the supplemental water they receive.
Most of our popular evergreens, more correctly known as conifers, evolved in locations that receive more precipitation than we receive in Denver. This means that for them to be healthy and prepared to resist insects and diseases, we need to drag out that hose during prolonged warmer periods in winter when the ground isn’t frozen and there is no snow cover. Insert a large screwdriver to determine how moist or dry the soil is. A simple frogeye sprinkler will do the job of getting water to the roots.
Because our heavy clay soils prevent tree roots from going deep, most roots extend only a few feet below the surface and radiate outward from the trunk at least as far as the height of the tree. In many cases, that means much of the yard needs to be watered.
Do your conifers a favor this winter and give them an occasional drink if it’s dry. They’ll be healthy and beautiful and an asset to your property.