Barbara Braznell walks her dog, Bou, in South Park near the Douglas County Courthouse. While a few trees in the park are awash in autumn splendor, many trees in the area have yet to change colors. Warm weather is a key reason for the late arrival of colorful fall foliage this year.

Ah, the joys of fall. Football and pumpkin hunts. Snug sweaters and apple cider. And green leaves?

Fall is indeed a late bloomer this year. Stan Ring, assistant horticulturist with Douglas County Extension, said that’s because of a wet spring and an unseasonably warm fall.

“We had early spring rains and now we’ve had some really warm fall weather,” Ring said. “We’ve had no cold days and very few cold nights (in the fall), and that’s actually what makes the leaves turn.”

That, and some biological processes.

“It’s been so warm the chlorophyll hasn’t changed,” said arborist Newton Mulford of Mulford’s Tree Service. During the warm months of the year, trees produce a chemical called chlorophyll, which gives them their green hue. As the weather changes, it becomes too dark and dry for photosynthesis to occur, cutting off production of chlorophyll and turning the leaves brilliant red and orange.

“As far as color goes, I think we’re a little late,” Mulford said.

The autumn delay won’t last long, said Mark Graves, senior forester for the city of Lawrence. He predicted a color change in a week or two, in time for Kansas University’s homecoming Nov. 3.

“Once we see a freeze or extended cold snap, we’ll see color change,” he said. “A heavy frost will make a rapid color change.”

Gabby Fraira, a groundskeeper at the West Hills apartment complex, 1012 Emery Road, said he noticed an abundance of green leaves at his property in McLouth.

“It’s still a little bit early,” he said, adding that he thought the weather was to blame for the late color change. “Every year the climate is different.”

Jennifer Smith, head horticulturist for K-State Research and Extension in Douglas County, said the color of leaves often depends on the length of the day.

“A lot of plant functions are related more to the amount of light they receive, instead of exposure to moisture,” Smith said. “Sunny days and cool nights all affect the intensity of the color, but they don’t cause the reaction to begin.”

She said the lack of colorful foliage might be part of the imagination.

“Cooler temperatures make us think that it’s already fall,” she said. “I think it’s going to start changing in a couple of weeks. I think if it’s 80 degrees, we wouldn’t be asking why they haven’t changed.”

People planning on attending this weekend’s Baldwin City Maple Leaf Festival might see more green leaves than they are used to. Maple trees tend to change in the middle of the season, Graves said.

But, he said, “Maples will stay green longer when we have a late rainfall.”

The recent rainfall will make for an ideal fall season, Graves said.

“I think it’ll be one of the nicest falls in recent years because of the amount of rain,” he said.