Below are a few questions often asked when trees are stressed by water deficits. Answers to those questions follow.
What are a few signs of water-related stress? Tree symptoms that indicate stress from water deficits are browning of leaf edges, absence of new growth in the spring, and dieback of leaves, twigs and branches.
How do I know the tree needs water? Dig or probe the soil 6 to 12 inches deep near the dripline of the tree. Is the soil moist? If so, do not water and wait a week or so to sample again. Contrary to popular belief, most tree roots and root biomass occurs in the upper 18 inches of the soil, not in a tap root.
How often should I water? The answer depends on the species of tree and the soil texture and structure.
As a general recommendation for Tennessee, most trees should receive an acre-inch of water every week, through precipitation or watering. An acre-inch of water is 27,154 gallons. Dividing gallons by square feet per acre (43,560) results in 0.62 gallons per square foot. Thus, if you are watering an area that is 8 x 8 feet (64 square feet), one-acre inch, 0.62 x 64 = 40 gallons of water.
If possible, avoid frequent, light applications of water which encourages shallow roots that are more susceptible to summer heat stress. Less frequent, deep watering is preferred.
Where do I water for maximum benefit? Water the tree halfway between the dripline (and sometimes 10 feet or more beyond the dripline) and the trunk. Most of the feeder roots are not located near the trunk of the tree. A common practice in newly-planted trees is to only water the rootball, which does not create a favorable environment for the roots to extend laterally into the resident soil.
Can I overwater the tree? Most definitely. Too much water is just as bad as too little. Saturated soils exclude oxygen from the soil. Roots die without air. The soil should be moist, but not soggy or saturated.
Wet soils also promote roots fungi and disease.
During droughty weather, most trees will benefit from supplemental watering to relieve stress from water deficits. Most all tree species, regardless of size are affected by unusual weather conditions. A thoughtful summer regime of watering is necessary to maintain trees in a healthy condition.