Late summer rain bodes well for fall foliage display in Northeast Ohio this year

Plenty of mid-to-late summer rain bodes well for fall foliage this year.Joshua Gunter, cleveland.com

CLEVELAND, Ohio – Last fall’s leaf color in Northeast Ohio was spectacular and it’s shaping up to be that way again this year based on one critical determinant of the overall presentation – tree stress.

That’s according to Ethan Johnson, plant records curator at Holden Forests & Gardens, who began thinking about the next couple months after spying a staghorn sumac on the grounds of Holden Arboretum in Kirtland that was already turning a brilliant orange-red, likely due to the stress of being struck by a mower.

This year, “we’ve had really good weather for the trees,” he said, and that bodes wells for fall foliage. It has been warm, he said, and while much of the area experienced a dry spring, there has been plenty of mid-to-late-summer rain to make up for any lack of moisture.

That’s important, because if trees go into fall too stressed for moisture, they can end up dropping their leaves early, he said.

He said it’s often beneficial for the soil to be a little dry during spring, so tree roots don’t get waterlogged.

What’s still too early to predict is how intense the colors will be this fall. That will depend primarily on the number of sunny days and cold nights there are starting in late September through October.

In general, there are three chemicals, or pigments, that come into play when setting the stage for fall color - chlorophyll, anthocyanins and carotenoids.

Chlorophyll in leaves convert sunlight into sugars through photosynthesis, providing the tree with food. It also gives the leaves their green color. Carotenoids help protect chlorophyll from getting too much sun, “so it doesn’t just bleach out the leaves,” Johnson said, while theories suggest anthocyanins also protect chlorophyll and act as an antifreeze during cold weather.

While sunny days give the trees more energy to produce the carotenoids and anthocyanins, the cold nights are what cause the chlorophyll to start degrading, making the other pigments visible, said Juliana Medeiros, plant biologist with Holden Forests & Gardens.

Carotenoids will turn leaves yellow, bright red and orange, while anthocyanins present as pink, scarlet, purple and blue.

Temperatures, as always, will also be a factor in the annual leaf show.

A light frost can actually be a benefit to the changeover, Johnson said, “because it’s a wake-up call” for the leaves to start their transition. But if it gets to cold, say from a hard frost, it can shut everything down.

“If it gets into the lower 20s the game is up,” Johnson said.

Johnson said sugar maples are the star performers at Holden Arboretum when it comes to fall foliage. They typically turn orange, orangish-red and yellow.

“Sugar maples are very colorful and sometime they have all those colors on the same tree,” he said.

Among the earliest trees to change color are tupelos, he said. Their leaves turn a bright, glossy red, but can also become orange.

“The ash are very early for our native trees,” Johnson said. White ash turns “pulplish,” while green ash turns yellow.

Peter Krouse covers the environment for cleveland.com and The Plain Dealer. Read more of his stories here.

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