How weather, location can affect a tree's fall colors

Many communities are embracing the harvest season this weekend with autumn-themed festivals, but Mother Nature isn't quite ready to unveil the breadth of her fall foliage.

While some trees are starting to show hints of color, most leaves have yet to transform into their vibrant displays of red, orange, purple and gold.

That's not entirely unusual for the beginning of October, especially considering the area's recent weather patterns, said Ed Hedborn, plant records manager for the Morton Arboretum in Lisle. As the days get shorter in the weeks ahead, he said, the biggest determinants for how the fall colors will present themselves will be the temperature and environmental conditions.

“Every year is different,” Hedborn said. “To me, it's enjoyable to wait and see what nature has to show us that given year.”

Here are the answers to some key fall color questions ...

When do we usually start seeing some color?

Leaves change as the tree begins preparing for the winter, a process triggered by decreasing day length, Hedborn said.

The second week of October is when you'll typically have the greatest variety of plants developing their fall colors in the Chicago area, he said. On a healthy tree in the right environment, the leaves can last 10 days to a couple of weeks before dropping.

Which weather conditions will give us the best colors?

Bright, sunny days and cool, but not freezing nights are ideal. A few consecutive days of that weather, and leaves will start revealing their pigments quite rapidly, Hedborn said.

Consistently cloudy, cold days and nights are likely to result in muted colors, he said. Same goes for unseasonably hot and dry conditions, which also could lead to an earlier leaf drop.

What other factors come into play?

A plant's health and location can make a big difference.

Plants that are under more stress will tend to turn colors earlier in the season than those in natural areas with optimal growing conditions, Hedborn said.

A tree in a forest preserve, for example, will change later than the same species in a parking lot median, where the root system is restricted and there's less water available. Or your front-yard landscaping could start producing color before the plants in your larger, more open backyard.

Severe weather, such as the polar vortex this past winter and record spring rains also could affect a tree's health, which could impact its fall color, Hedborn said, though it depends on the individual plant.

“Just like how humans react differently to different stressors,” he said, “plants are the same way.”

Does the tree's species matter?

There is a sequence for when certain types of trees typically change, Hedborn said.

It starts with sumacs, the colony of plants found along the side of the road that turn bright red. Those sometimes change in late September, given the right conditions, he said, though they're just beginning to transform now.

“They're a little behind, but not by much,” Hedborn said.

Then come redbuds, hickories and Ohio buckeye trees, followed closely by honey locusts and ashes. Sugar maples “really come into their own” by mid-October, he said, and as they start to fade, oaks become more colorful.

Where can I see the best fall colors?

State parks and preserves are always a safe bet in searching for majestic autumn displays, Hedborn said, pointing to Starved Rock or Zion's Illinois Beach State Park. Even natural areas, such as Goose Lake Prairie in Grundy County, will show some fall foliage.

The Morton Arboretum in Lisle has trees and plants growing from all over the world, Hedborn said, giving visitors an expansive fall color palette. Its website contains a “fall color report” that is updated regularly throughout the season.

“You can find fall color wherever you look,” he said. “Nature is pretty incredible with the fall displays she presents to us.”