Locust trees are dropping leaves. Aspen leaves are browning and look desiccated. Poplar and maple trees are showing fall colors. What's going on?
Although the warm temperatures make us feel as if summer is never going to end, autumn is on the way. The days are getting shorter, and many plant processes are triggered by day-length. However, there are also stress factors at work. With wind and high temperatures, the water-pumping mechanisms of trees are working overtime to meet the trees' water needs. Sometimes, even with adequate soil moisture, a tree just can't pull enough water out of the ground fast enough to replace what is transpiring from its leaves in a effort to cool the leaf surfaces and keep the cells turgid (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 irrigation.
When leaves have brown edges, there may be an accumulation of salts in the root zone of the tree, due to shallow watering, overfertilizing or naturally occurring salts in the soil. Trees shed leaves in midsummer if they do not have enough water available in the soil. Deeply soaking trees each week with extra water and mulching the areas around them can help reduce trees' water stress. However, be wary of overwatering. Sometimes, people give more and more water to trees that look wilted, not realizing they have rotted the roots, making the tree unable to absorb water. Then, the trees look drought-stressed, so people add even more water!
Instead, dig a hole under the canopy of a tree, 8 inches to 10 inches deep, and see if the soil is moist. A tree needs water from the trunk out to the farthest reach of the branches, to a minimum depth of 15 inches. Often, we have trees on drip systems, with one or two emitters per tree. We run the system three times a week for 20 minutes, equaling one hour for the entire week. If the two emitters per tree have a two-gallon-per-hour flow, each tree is only receiving two gallons of water per week, when temperatures are close to 100 degrees! That is terribly inadequate, especially knowing that poplars, aspens, maples and birches are water-thirsty trees and can absorb hundreds of gallons of water each week.
Water deeply and thoroughly when you water your trees. Remove lawn from the trunk out to the drip line. Place mulch in the areas surrounding trees to hold in soil moisture. Trees that lose leaves now will most likely be fine next year if you continue to water properly through the seasons.
Information, 887-2252 or skellyj@unce.unr.edu, or your local University of Nevada Cooperative Extension office. Check out horticulture publications at www.unce.unr.edu. Ask a Master Gardener at mastergardeners@unce.unr.edu
n JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.
