Jeff Burbrink

Great Outdoors



Over the past few weeks, I have written about the effects of drought on corn, soybeans and lawns. Today I want to discuss tree care during a drought.

Symptoms of drought injury to trees can be sudden or may take up to three years to be revealed. Drought injury symptoms on tree leaves include wilting, curling at the edges and yellowing. Deciduous trees (those trees that lose their leaves in the fall) may develop scorch, which is a browning of outside edges or browning between veins, and may eventually brown the entire leaf.

Evergreen needles may turn yellow, red or purple. They may also turn brown at the tips of the needles and browning may progress through the needle towards the twig. In continued drought, leaves may be smaller than normal, drop prematurely or remain attached to the tree even though brown.

Often times, drought stress may not kill a tree outright but set it up for more serious secondary insect and disease infestations in later years. After the 1988 drought, I saw trees exhibiting damage from drought stress for three years or more.

Healthy trees are among the last plants in the area to show drought symptoms because the trunks can store tremendous amounts of water. That same characteristic means it is also more difficult to re-hydrate a woody plant once it uses up most of its stored water.

The first trees to water are those that will be most vulnerable and affected by dry conditions.

Newly planted and young trees (1 inch to 6 inches in diameter) are not yet established and have a limited root system. These trees generally need supplemental water even when we are not experiencing drought conditions. Generally it will take one full year per inch of trunk diameter to get established. For example, it will take three years for a 3-inch-diameter tree to establish itself.

Trees growing within a restricted root zone such as trees adjacent to a driveway or house, growing within a landscape strip between your sidewalk and the street or growing in a median or traffic circle will need supplemental watering if they recently received root injury due to construction work.

Here are tips on how and where to water trees:

• Deep watering to a depth of 12 inches below the soil surface is recommended. One inch of water applied slowly will wet the soil to a depth of about 12 inches. Saturate the soil around the tree within the “dripline” (the outer edges of the tree’s branches) to disperse water down toward the roots.

• For evergreens, water 3 inches to 5 inches beyond the dripline on all sides of the tree.

• The objective is to water slowly, dispersing the flow of water to get the water deep down to the trees roots. Watering for short periods of time only encourages shallow rooting which can lead to more drought damage.

• Don’t dig holes in the ground in an effort to water deeply. This dries out roots even more.

• Watering immediately around the trunk of a mature tree doesn’t help much either. Most of those roots hold the tree in place and do not contribute much to water uptake.

Once the rains start up again, do not forget about your trees. Drought-stressed trees will benefit from water until the ground is frozen this winter. Remember, it takes a long time to re-hydrate a tree.

Next week’s column will cover the subject of drought’s effect on wildlife.

Jeff Burbrink is an Extension educator at Purdue Extension Elkhart County, 17746 C.R. 34, Goshen, IN 46528. Contact him at 533-0554, 533-0254 (fax) or jburbrink@purdue.edu.