“I think we’re going to have a good fall color year because of the weather we’re having,” Goerndt says. “You get the best and brightest colors when you’ve got the kind of fall weather we have now where you get sunny days and crisp, cool nights.
Typically, the best fall colors are in Northeast Iowa, but there are some good areas in Central Iowa too, says Goerndt.
Leaves will change across north Iowa between the last week of September to the second week of October. Central Iowa will see leaves changing from the first to third weeks of October. Southern Iowa will see leaves change from the second week to the end of October.
What changes where is subject to weather. How vivid and how long leaves remain is also determined by weather.
As days get shorter, trees release a chemical called phytochrome. This chemical slows down chlorophyll production and allows the tree go dormant. The loss of chlorophyll (which is green) allows the colors of the leaf to show.
Leaf pigment is also influenced by the amount and acidity of sap in the trees. More acidic sap gives trees more reds and brighter colors. Less acidic saps gives trees duller and more yellow colors.
Leaf watching season can be cut short by drought and/or strong wind events.
“Drought can also cause the colors to be less brilliant,” says Goerndt. “When trees are stressed, the leaves tend to turn brown and fall off. In areas where there’s severe drought, we’re seeing early leaf drop.”
The DNR has a fall colors hotline which can be found, along with other information, at: www.iowadnr.gov/Environment/Forestry/ForestryLinksPublications/FallColor.aspx