Apply water slowly and infrequently. Sprinkler watering not only loses significant amounts of water through evaporation, but wets bark at the base of the tree, increasing possible damage from disease and pests.
Use soaker hoses or drip irrigation instead of sprinklers. Soaker hoses and drip irrigation systems allow water to penetrate slowly into the ground, getting the maximum amount of water to the tree roots where they are needed and minimizing waste.
How much to water. Insert a soil moisture meter into the soil about halfway between the trunk and the drip line. If the meter reads “moist” or “wet,” then stop watering. These meters are inexpensive and can be purchased at nurseries, online and big box stores. Alternately, use a six-inch screwdriver. Insert the screwdriver into the soil at the same place as you would the moisture meter. If it goes in up to the handle, the tree needs no water.
How to water. Run a drip or soaker hose around the tree, starting at the drip line of the tree (at the end of the farthest branches). Stop at four to five feet from the trunk.
Organic mulch. Organic mulch helps keep moisture in the soil, and helps protect the roots from high temperatures. Spread it three inches deep but keep the mulch at least a foot from the base of the tree.
For more information, see the Texas Forestry Service article on tree irrigation.