Here are some general guidelines to help your trees survive the pending summer heat.
As Midwesterners know, summers can get dry in Kansas, and many trees go into a "summer dormancy." Usually, August is when excess leaves are shed and the trees essentially shut down. No problem. However, this year I noticed that leaves were starting to fall several weeks ago and continue to do so. This is a sign of a tree in trouble, and something may need to be done.
Concentrate your efforts on recently planted trees and shrubs. Even trees planted two and three years ago have not established the extensive root system needed to absorb enough water when the soil is dry and the leaves are exposed to hot, dry winds. These trees will benefit from a deep, but infrequent watering.
Deep watering can be done most efficiently with a soaker hose, but an ordinary garden hose set on a slow trickle also will work well. The key is small amounts of water, applied over a couple of hours. As a general rule, apply 5 gallons of water for every year the tree has been planted, up to a maximum of 20 gallons.
It may be helpful to set the oven timer, so you remember to move the hose or shut off the faucet. If you are seeing surface runoff, reduce the flow or build a berm with at least a 4-foot diameter at the base of the tree to allow the water to percolate down through the soil, instead of spreading out. Watering like this should be done once every two weeks.
If your established trees are mulched and the soil is still damp, they may not need any additional water -- yet. It is important to check under the mulch by using the probe test. If it is not easy to push a long screwdriver at least eight inches into the soil, then it is dry and watering is needed. I would rather water now than later, after drought damage (scorched leaves and twig dieback) has already occurred and the tree is shutting down for summer dormancy.
-- Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.