Protect Landscape Trees Now from Drought Injury

Adapted from an article by Dr. Kim Coder

Professor of Tree Health Care, Warnell School of Forestry and Natural
Resources, UGA



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 from drought injury.
Trees also 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.



For more information:



Shade Tree Decline - http://apps.caes.uga.edu/urbanag/index.cfm?storyid=2714



What's Wrong With My Tree? -
http://apps.caes.uga.edu/urbanag/index.cfm?storyid=2504

 --
Dr. Teri Hamlin
North Region Agriculture Education
Georgia Department of Education
204C Athens, Ga 30602
706-542-3679 / 706-540-0032
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