Lexington, KY - What a summer and early fall we've had. Sun, sun and more sun. Have you found yourself wondering if it will ever rain again? Our trees have been asking this question for months now.
The effects of drought can be recognized throughout a tree. Drought-stressed trees are more susceptible to attacks from disease, insects and other pests. Growing periods with little water can lead to decreased rates of growth and the disruption of photosynthesis and normal functions, such as the maturing of fruit and going into dormancy at the appropriate time.
Healthy trees are essential to the well being of our community. This is no small matter. Our urban sites have lots of stresses that aren't found in natural systems. Healthy landscapes require appropriate management practices. It is a lot easier and less expensive to keep trees healthy than to try to cure them once they become stressed from drought or other problems.
How would a tree in the Bluegrass define the term drought? "While a meteorologist might disagree, after 10 days without rain, it's the beginning of a drought as far as your tree is concerned," according to Dr. Bill Fountain, a professor of arboriculture at the University of Kentucky.
This comment is specific to the Bluegrass area, where the soil sits on fissured limestone bedrock. "We don't have a water table because water permeates the soil, runs along the surface of the bedrock until it finds a crack, and then it's gone," Fountain said. Thus, our soils tend to dry out quickly.
The time to start watering your trees was back in July, after those first 10 days without rain, before they began to wilt. Dave Leonard, a local consulting arborist, advises watering 1 to 1.5 inches per week to maintain soil moisture at a healthy level during periods of low rainfall. The goal is to wet the soil down to about 6 inches. However, Dr. Fountain warns that in a bone dry soil, 1 inch of water may wet only 2 inches of soil. Guessing is not good enough; it's best to check. To be sure of the effectiveness of your watering, you can dig down into the soil to check the depth of water penetration. It is important to use water prudently, so concentrate your watering on the area under the drip line, since this is where 80 percent of the tree's roots are located.
Water with a sprinkler. It is best to water in the very early morning when the dew is still on the leaves so that your watering does not extend the normal period of leaf wetness.
Back in the early fall, if you hadn't been watering your trees and you had early defoliation, it was best not to start watering, since this can push out new shoot growth which would then be killed in our first frost. However, around mid-November, when the cold weather sets in and new shoot growth will no longer occur, it is a good idea to water. Most root growth occurs when the soil temperature is 32 to 50 degrees Fahrenheit, but water is essential for this to occur. In fact, roots can grow at any time during the winter as long as the soil is not frozen.
And what about fertilizing your trees? Fountain says that a tree under urban stress may benefit from additional nitrogen to encourage leaf growth but, in general, mature, established trees do not need to be fertilized in order to maintain their health. Stressed trees should be fertilized in October or November.
By fertilizing in the fall, nutrients will have a chance to be absorbed by the roots and will already be in the ground when the roots resume functioning in the spring. Fertilizing in the spring can result in shoot growth at the expense of root growth. When we encourage shoots to outgrow roots, we are setting the tree up for failure in the next drought. However, right now our soil is so dry that these nutrients will not be available to the tree roots, which further emphasizes the need for irrigation in dry late falls and winters.
Be sure that you have mulch rings around all of your trees. Ideally, these rings should extend to the drip line, but that is not always possible. Mulch helps to maintain soil moisture and protects trees from mower damage. Mulch should be two to four inches deep, no more, and it should never touch the trunk of the tree. The "mulch volcanoes" you see around town are not only unattractive but they will damage the long term health of the tree.
Proper pruning helps to ensure a healthier, more drought tolerant tree. Leonard notes that trees in our yards do not develop the way they would in a forest, with other trees nearby. Branches that are unhealthy, dead or dying, or growing incorrectly should be eliminated. Be sure the person working on your trees is an International Society of Arboriculture (ISA) Certified Arborist.
We need more trees. Our urban forest is in major decline. For guidelines on selecting and planting a new tree, visit Leonard's website at www.dlarborist.com/urbantree.html. The ISA website, www.treesaregood.org, has additional information on a variety of topics.
We must take care of the trees we have. The well being of our community, now and in the future, is at stake. Proper watering, mulching and pruning will help to preserve these trees while our new ones are growing.