Expert explains what is going on with leaves hanging on

Mother Nature and Jack Frost are at odds this season. The result: Trees hanging onto their leaves.

At Cornell Cooperative Extension of Monroe County, Walt Nelson explained what’s going on with the deciduous trees — those oak, maple, elm and others that are supposed to drop their leaves in the fall.

“Many areas of New York, including the Greater Rochester area, had a different fall in 2017,” said Nelson, the extension’s horticulture program leader. “Summer-like weather extended into October, abruptly ending the growing season with freezing temperatures in early November.”

He said that typically, cooler weather and shorter day length stimulates the formation of an “abscission layer” of cells where the leaf stalk joins the twig. That layer acts like a tourniquet, causing the leaf to break from the twig. But this year, that crucial layer that sends leaves falling to the ground didn’t form — or formed badly — leaving leaves and twigs intact.

After the warm early fall and then a freeze right after Halloween, there was no gradual move into fall, Nelson added. “Everything was still growing,” he said. That was the impetus for what happened. He mentioned that while shorter days are indeed a factor in prompting leaves to fall, it is not the only driving force and colder weather is also needed.

Nelson said this situation is usual and he can’t recall another autumn quite like this. He added it’s unlikely this will affect the health of the trees in the long run. “This may be another example of our changing climate or just another anomaly of weather in much of New York,” he said.

In the short term, these leafy trees could suffer if they’re hit with wet, heavy snow. Sloppy snow sticking to leaves could bring down branches under the weight.

“We can hope for some really nice breezes to get those leaves out of the trees,” he said. “Winds will likely tatter leaf blades and sometimes tear the leaves from those trees. Others may hang on until next year’s expanding buds push those leaves from the tree — characteristic of red oaks. If those leaves hang on and if we get a wet sticky snowfall, there could be resulting storm damage.”

In the city of Canandaigua, City Manager John Goodwin said those hanging-on leaves “are complicating a lot of municipal leaf schedules.” Crews have done two complete leaf sweeps of the city this fall and there will be more. Crews will continue to pick up as long as weather allows, he said. He advised people to pile leaves in the right-of-way and away from storm drains.

Edith Davey, an educator with Ontario County Soil and Water Conservation District, reminded people to keep leaves out of storm drains, the lake, gullies and streams. Shredding and composting leaves is a good option, she said. The leaves make a healthy cover for gardens.

“Leaves will decay and break down,” she said. “They are great mulch, it is nature recycling.”