JoAnne Skelly: What’s wrong with my trees?

Trees are dropping leaves or needles. Leaves may be turning brown. Some are showing fall colors. What’s going on with trees?

The days are getting shorter, and many plant processes are triggered by day-length. However, there may be stress issues at work as well. With wind and high temperatures, the water-pumping mechanisms of trees are working overtime to meet the water needs of plants. Sometimes, even with adequate soil moisture, a tree just can’t pull enough water out of the ground fast enough to cool leaf surfaces and keep cells full of water. On the other hand, there may not be enough water in the soil for the tree to draw on due to insufficient deep irrigation.

If leaves have brown edges, salts may have accumulated in the root zone of the plant due to shallow watering, over-fertilizing or naturally occurring soil salts. Deeper watering will help. Trees shed leaves in midsummer if they do not have enough water available in the soil. Deep soaks with extra water every week and mulched areas around plants can reduce water stress. However, be wary of overwatering. Sometimes wilting is caused by damaged roots and more water can’t solve the problem. Carefully dig a small hole under the canopy of the tree, eight to ten inches deep, and see if the soil is moist. A tree needs water from the trunk out and around to the furthest reach of the branches to a minimum depth of 15 inches. If trees are on a drip system with only one or two one-gallon per hour emitters, and the system is run three times a week for 20 minutes a time, that’s only one to two gallons of water per week. If temperatures are close to 100 degrees, that is terribly inadequate, especially since poplars, aspens, maples and birches are water-thirsty trees. They can absorb and use hundreds of gallons of water per week.

If soil moisture seems good, note that trees sometimes shed their leaves from the center of the tree outward when not enough light can penetrate to the interior of the tree to support photosynthesis.

Water deeply, thoroughly and separately from the lawn when you water your trees. Add more and larger drippers. Remove lawn from the trunk out to the dripline. Mulch that area to hold in soil moisture. Trees that lose leaves now can be fine next year if you continue to water properly through all the seasons.

JoAnne Skelly is associate professor & extension educator, emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.