Periods of drought are common on Colorado's Front Range. This area is naturally a semi-arid, shortgrass prairie that would have few trees without irrigation. A visit to Cathy Fromme Prairie Natural Area (photo) or the Pawnee National Grassland will help you visualize what this area would look like without our extensive urban forest. Many of the tree species planted in our communities thrive in regions where rainfall exceeds 30+" annually. The Fort Collins area receives on average 15 inches annually. Most established, drought-tolerant trees require 22-25 inches of moisture per year to grow at a moderate rate, so supplemental irrigation is needed for most landscape trees.
Water stress affects most of the physiological processes involved in plant growth. The symptoms of drought injury to trees may be sudden or may take several years to be noticeable by homeowners. Initially, you may notice the leaves beginning to wilt, followed by chlorosis (yellowing), browning & scorching. In conifers you will probably notice yellowing and browning on needle tips.
During a prolonged drought, leaves may be smaller than normal and may drop prematurely or remain attached but exhibit a brown or scorched appearance. As the drought continues, there will be a reduction in photosynthesis processes followed by a reduction in root, shoot, height and diameter growth. Under continued drought conditions, plants suffer chronic stress and are very susceptible to secondary disease and insect pest infestations. A severely stressed tree will be unable to defend itself against these secondary pests and will often die.
In the past, our shade trees received adequate water via excessive turfgrass irrigation. However, the current drought has forced us to become more aware of our limited water resources. We need to adopt a more sustainable landscape management technique (Xeriscaping) appropriate for our semi-arid high plains climate.
Since many communities are implementing outdoor water restrictions, trees should be given a higher watering priority than your lawn. Please keep in mind that turfgrass will go dormant under drought conditions. If you lose your turf to drought, it can be replaced in a matter of months, BUT it will take 20 years to replace a 20-year-old tree!
Ensuring the long-term health of your trees begins with using best planting practices. Think of your shade trees as a lifetime investment that requires a lifetime of care. We have developed the following information to help you care for your trees in our semi-arid environment: