Botanist explains why leaves are slow to change color this year

MADISON, Wis. — Leaf colors in Wisconsin are slow to change this fall, and it’s prompting questions about if and when it will happen at all this season.

Botanists say if weather conditions are warm and favorable, trees will use sunlight to produce sugar and stay green.

Record-breaking 90-degree weather in September has contributed to the delay in changing colors.

“If it’s warm and there’s enough water and there’s plenty of sunshine, the plant continues to make food and remains green by keeping chlorophyll in the leaves,” said Dr. Ken Cameron, chair of the University of Wisconsin-Madison Botany Department.

Some plants were too stressed by the heat and dropped brown leaves without even changing color, Cameron said.

Cameron said three things are needed for the leaves to change color: the right balance of temperature, moisture and sunlight.

“The plant needs to convert some of its sugars into a red pigment called anthocyanin,” Cameron said. “We also need the nights to get fairly chilly and that will initiate a breakdown of the green chlorophyll pigments in the leaves, revealing the yellow and the orange.”

According to the Travel Wisconsin Fall Color Report, only six counties have 85 to 95 percent of fall color.

Eleven counties in the state, including Dane County, are showing mostly green trees.

Cameron said it isn’t too late for trees to change color if temperatures cool down soon.

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