Stressful heat culprit behind falling sycamore leaves

Sycamore tree leaves cover a lawn along Village Drive in Prairie Village.

It may be mid-July. But for some local homeowners, it’s starting to look like early October on the front lawn.

Weeks of early summer temperatures that have frequently pushed 100 degrees have prompted several tree species to start shedding their leaves months ahead of schedule. The leaf drop, says K-State Extension horticulture specialist Dennis Patton, is a stress response intended to help the trees preserve precious water as they ride out the drought conditions.

“We tend to think of leaves as this sign of vitality and know how important they are in creating energy for the tree and producing oxygen,” he said. “But what they also do is lose water.”

Locally, sycamores, birches and member of the cottonwood family are most susceptible to dry conditions because their natural habitat is in lowland areas with moist soil. They are among the trees along Village Drive in Prairie Village and scattered throughout Mission Hills that have started to shed their large leaves early.

Patton notes that, for now, at least, the heat isn’t likely to pose risk of permanent damage to the trees shedding their leaves.

“The heat drop is natural and it won’t kill them,” he said. “We don’t know how stressful the rest of the summer will be, though. We’re a month ahead of schedule getting into the stressful part. It’s hard to tell when that stress-induced dormancy could turn into a stress-induced dieback.”

And, he adds, the trees shedding their leaves aren’t the ones most likely to be killed by the drought. Evergreen trees have no natural response to conserve water during extended dry periods.

“You can’t tell they’re stressed until they’re dying, and then it’s too late,” he said.

To help evergreens make it through the summer, Patton suggests giving them a deep-soak watering every three to four weeks. Leave the sprinkler on all day and change its location four or five times to saturate the ground surrounding the tree, or take a hose and put it on trickle, moving it around the yard. The trick, Patton said, is to ensure the soil below the top four or five inches receives water so that it can feed the trees’ deeper roots.