Watering Urban Trees
As temperatures rise, trees need water to stay healthy. Many mature native trees are able to survive periods of drought, but most will benefit from some supplemental water after 4 to 5 weeks without rain. The quantity of water needed to keep your grass alive may not be enough for your trees.
You can use a screwdriver to determine if the trees need more water. If you can push the screwdriver at least 6-8 inches into the ground, then the soil is sufficiently moist to sustain your trees. The screwdriver won't penetrate the ground when the soil is dry. Check the soil moisture frequently to determine when it's time to water.
These detailed watering instructions for trees were published by the Texas A&M Forest Service in 2011 during one of the worst droughts in Texas history. They offer easy-to-use instructions on how to water with a sprinkler, garden hose, soaker hose or 5 gallon bucket. This three and one-half minute video from the Texas A&M Forest Service provides the same information.
It's normal for many trees to drop some leaves during extreme heat. If leaves start raining down from your oak, though, it could be oak wilt. Call an Oak Wilt Qualified Arborist to schedule an inspection.