Protect Landscape Trees from Drought Injury

Source(s): Kim D. Coder, Professor of Community Forestry, Warnell School of Forestry and Natural Resources, The University of Georgia

 

---

Trees across Georgia are declining due to drought. Drought stressed trees may have fewer or smaller leaves. Small or large limbs or the entire tree may die. Although trees can withstand some drought injury, some trees may require months to years to recover. Trees may not show damage immediately. When they do, it may be too late to save them. Protect trees now from drought with proper care.

How to Water

The best ways to water trees are by soaker hose or drip irrigation. Automated lawn sprinklers are less efficient for applying water to trees. Even a garden hose, moved often, can provide a good soil soaking. Use a light organic mulch to conserve moisture and apply water over the top of the mulch. Do not pile mulch against the base of the tree or allow water to concentrate at the base of the trunk as this can lead to pest problems.

Where to Water

Most of the tree’s absorbing roots are in the top foot of soil. Applying water deeper than this misses the active roots and wastes water.

Lay-out water hoses or applicators out to the tree crown edge (drip-line). Water the soil areas directly beneath the foliage and shaded by the tree. Do not water beyond the drip-line and do not water closer than 4 feet to the trunk base on established trees.
Use mulch and slow application rates on slopes, heavy soils (clays), and compacted soils to assure water is soaking-in and not running-off. Do not spray tree foliage when applying water. Water droplets on tree leaves can lead to pest problems. Try not to wet the tree’s trunk.

Young, newly planted trees need additional watering care. Water has limited horizontal movement in soil. You must apply water directly over where you need it in the soil. For new trees, concentrate water over the root ball, as well as the planting area.
Old, large trees can be watered over the entire area under their foliage. Another method in watering large trees is to water roughly 1/3 of the area within the drip-line.

When to Water

The best time to water is at night from 10 p.m. to 6 a.m. Trees refill with water during the night. Watering at night reduces losses to evaporation and assures that more water moves into the soil and tree.

For every 18°F increase in temperature, the amount of water lost by a tree and the site around it almost doubles. Consider this when watering trees. Trees surrounded by pavement and other hot, hard surfaces can be 20-30°F warmer than a tree in a protected, landscaped backyard. Water use rapidly climbs with increasing temperatures, and so should water application volumes.

How Much To Water

Depending upon soil texture 1 to 2 inches of water per week should sustain a tree. Trees in limited rooting areas, in containers or pots, or on major slopes, need additional care to assure water is reaching the root system in adequate amounts and not suffocating roots from lack of drainage. Five gallons per square yard is about 1 inch of water.

Fine soils (clays) require careful attention to prevent over- watering and root death. Sandy soils can dry out rapidly since water runs out of the rooting zone quickly. Composted organic mulch on the soil surface can help prevent rapid loss of applied water.

How Often To Water

Water trees once or twice a week (minimum of 1 inch per watering) in the growing season if there is no rainfall in that particular week. A few heavy waterings are much better than many light, shallow waterings. A greater proportion of the applied water is used by the tree with heavy, infrequent watering. Once you begin watering, continue to water until rain comes.
Drought is the main cause of tree decline but beware of other factors that damage roots and lead to long-term tree decline and death.

• Do not fertilize or use pesticides on severely drought stressed trees.
• Do not dig or drive under the canopy of trees or do other things that kill or crush roots.
• Do not pile soil under tree canopies. When adding soil to cover roots etc., add no more than 1 inch per growing season. Protect the critical root zone of the tree. Measure the trunk diameter at chest height in inches. Multiply this by one and a half. This will be the size in feet of the radius of the circle that you must protect around the tree. For instance, a 20 inch diameter tree would have a critical root zone with a radius of 30 feet. Avoid digging, piling soil, trenching or driving through this area.

Call your local Extension Agent at (800-ASK-UGA1) or Locate your local Extension Office Georgia Extension Office Locations

---

Center Publication Number: 267