   Tree Irrigation and Care - February 14, 2007 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Northern Arizona is still in a state of prolonged drought and landscape trees require irrigation to survive extended dry periods. Proper irrigation practices can help trees become more drought-tolerant by encouraging root systems to occupy a greater soil volume. By following a few simple guidelines, you can promote tree health and beautify your surroundings. Tree root systems do not typically have large, carrot-like tap roots. Healthy tree root systems spread 2 to 3 times wider than the height of the tree and most of the tree’s water absorbing roots are in the top twelve inches of the soil. To encourage these broad, shallow root systems, water should be applied at the tree’s dripline and slightly beyond if possible. Apply water deeply and slowly as to irrigate the root zone to a depth of at least 12 inches. Apply water to many locations under dripline. On relatively level sites, basins can be used for flood irrigation, but make sure the basin is placed at or beyond the tree’s dripline. You may also consider an inner berm to prevent water from pooling near the trunk. Soaker hoses or soft spray wands are effective irrigation tools. Other devices are designed to deliver water below ground (deep root forks or needles). If a deep root fork or needle is used, insert the device no deeper than eight inches into the soil. Drip irrigation is commonly used to establish young trees. These systems can be effective, but keep in mind that irrigation scheduling and drip emitter spacing is critical to effective drip irrigation of trees. In my experience, the tendency is to place one or two drip emitters near the tree trunk and not add additional emitters over time. This will not encourage the optimal root system described above. If you expand your drip irrigation system, do not move the original drip emitters away from the trunk without allowing new roots to establish near the dripline. This may take two growing seasons or more. If you have selected appropriate species and your irrigation is effective, there should be no need to fertilize your landscape trees. Fertilization encourages fast growth and creates greater leaf area. This growth will only increase water demand and will likely make the tree more susceptible to damaging insects or diseases. The only appropriate time to fertilize a tree is when you are addressing a specific nutrient deficiency. Do not prune trees unnecessarily. Pruning produces wounds which consume energy that would otherwise be available for metabolism and growth. These wounds are also entry points for insects and disease. Pruning can be necessary to prevent crossing and/or rubbing branches but is seldom effective at permanently reducing a tree’s size. Do not use pruning paints or sealers. These products actually retard the healing process. Resist the urge to remove lower branches from trees. These branches are directly responsible for increasing trunk growth below them. Retaining lower branches will increase trunk taper making it more resistant to wind and reducing the need for staking. If a tree is unhealthy or outgrown its space, consider replacing it. Often cottonwoods, willows, and mulberry trees have been planted for fast growth. These species often outgrow the available space or have been topped. These species are excellent candidates for replacement if they are not currently performing to your expectations. If there are multiple trees that need replacing, consider doing it over several years. As long as the site has full sun, older declining trees can be strategically removed and replaced with more suitable species as needed. Planting appropriate tree species can decrease water demand and increase the value of your property. Carefully consider whether to plant evergreens or deciduous trees. Deciduous trees can moderate indoor temperatures when placed on the south and west sides of your home. Careful planning and proper care will result in healthier trees that meet your objectives. Cooperative Extension has publications available on the subjects of tree species selection, proper planting, pruning, hiring tree experts, and more. Below are links to these publications. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at cottonwoodmg@yahoo.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site. Drought Tolerant Trees for Mid-elevation Deserts of Arizona (3,000 to 4,000 feet) (2001) (2 pp.) Pruning Deciduous Shade Trees (1999) (6 pp.) Planting Guidelines: Container Trees and Shrubs (1998) (2 pp.) How to Hire A Tree Expert (2001) (3 pp.) |