The recent rains did little more than tease us this week. And many gardeners continue to water as soil conditions are dry in and around the Lawrence area. In addition, many trees have damaged root systems from three years of drought and are struggling to use the water in the soil already.
If you have leaves turning yellow and falling, or entire branches that have lost their leaves, there is more bad news -- August. The excessive summer heat mixed with weakened roots not able to pull up water has damaged many mature trees. 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. However, this year I noticed 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 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 will work well also. The key is small amounts of water, applied over a couple of hours. As a general rule, apply five 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 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 8 inches into the soil, then it is dry, and watering is needed. I would rather water now, then later after drought damage (scorched leaves and twig dieback) has already occurred, and the tree is shutting down for summer dormancy.
If you are thinking about planting new trees this fall, here is a partial listing of drought-tolerant trees. Once established, the following trees have proven to be tough sturdy growers: oaks (specifically burr, white and red), black walnut, green ash, redcedar and other junipers, Goldenrain Tree, Ginkgo (male trees only) and Norway maple.