MINNEAPOLIS (FOX 9) – The days are getting shorter, kids are going back to school, and the Minnesota State Fair is starting. That means fall is just around the corner. It also means that the deep greens we’ve seen this year due to all the rain will soon turn to shades of yellow, orange, red—and then, of course, brown.
The rain could result in a spectacular fall foliage display this year, with colors lasting several weeks across the state. However, the heavy rain may also have a negative impact, as temperatures and precipitation in September are key to how great the colors will be.
Why some trees are already starting to change color
In the Twin Cities, trees are already starting to change color, but it’s probably not because they think it’s fall. Brian Schwingle, forest health program coordinator for the Minnesota Department of Resources, says this can and does happen in very wet years. While the extra moisture this year is very good for long-term plant health after three very dry years, it does add another year of stress to our tree canopies. But it’s a different kind of stress than in drought years because instead of fighting each other for moisture, trees are battling conditions that lead to easily transmitted fungal diseases.
Fungal leaf diseases generally kill off portions of the leaves (and cause brown spots or discoloration). These spots can combine and turn entire leaves brown, and sometimes leaves drop very early before they even have many leaf spots. Usually, fungal leaf diseases are not a problem for the health of the tree, but they do make it unsightly. This year, leaf diseases are quite severe and common in quaking aspen, balsam poplar, swamp oak in some areas, white oak in some areas, wild apple, lilac, and probably other species as well.
Schwingle explains, “When there is extreme rainfall or extreme drought in a growing season, we see color changes in parts of the tree canopy. This often happens as early as July and is a different process than the fall color of the entire forest. It is a response to stress and sometimes this happens before branches or trees die from the cause. This year, the fall colors appearing in summer could easily be a delayed response to severe drought damage starting in 2023. Drought can trigger or promote diseases on trunks, branches and roots, and these diseases sometimes take a long time to develop. On the other hand, the fall colors in summer could be a sign of root stress because the trees were flooded for too long this year.”
Will the colors be particularly bright this year?
Fall colors in Minnesota. (FOX 9)
A wetter and cooler summer is ideal for maximizing fall color potential. However, it’s too early to predict whether fall colors will be more vibrant this year. Schwingle says this is because the weather that most affects the “brilliance” of fall colors — especially reds — occurs during the leaf-shed period in September and October. However, because Minnesota has not experienced extreme drought to date, the potential for maximum brilliance is still there in trees that have not been affected by serious leaf diseases.
“To ensure bright fall colors, we want cool, clear days and nights in September with temperatures not falling below freezing,” Schwingle said.
Conditions that can drastically reduce autumn color brilliance include:
- An early hard frost in September
- A week-long rainy/cloudy/windy weather pattern in mid or late September
- After a few cool days, several days of hot/dry weather.
When does the color splendor in Minnesota reach its peak and where can you find the most beautiful colors?
Typical fall colors in Minnesota. (FOX 9)
The exact timing of the few days with the most vibrant colors can’t be predicted that far in advance in any given location, but that’s not to say we don’t have a general time frame. While there are many factors that cause trees to change color, the ultimate trigger is dwindling daylight. As long as the sun is shining, trees can produce chlorophyll, which is how they get energy from the sun. But as daylight gets shorter, they gradually produce less. Eventually, combined with overall cooler and drier conditions, this process takes long enough for the tree to realize that fall is here and go into hibernation. We see this transition into hibernation when the leaves change color and chlorophyll production stops for the year.
Because the waning of daily daylight hours is the primary reason fall colors change, there is a fairly consistent time frame for the color change in Minnesota. It often begins in northern Minnesota just after Labor Day and ends in southern Minnesota around Halloween. Peak times vary a bit from year to year, but are often the last days of September in the Arrowhead, then move further south, reaching peak colors around the Twin Cities often in the middle of the month. And then the color often stays the longest right along the Mississippi River in southeastern Minnesota until Halloween.
For the best colors this year, FOX 9 meteorologist Cody Matz recommends heading north. Unless something unusual happens, fall colors will be pretty bold across the region this year, but they might be a bit more brilliant up north. That’s because rainfall levels in the Arrowhead and Canadian Border region have been closer to average this year than the rest of the region. That means less stress on the trees and gives them a better chance of reaching their full glory in the fall. If you’re looking for more specific information, you can’t go wrong in the areas right at the tops of the low mountains from Duluth to Grand Marais in the Arrowhead — and this year has the potential to be stunning.
“An earlier, lighter frost will mean that the autumn colours will peak earlier, so pay attention to the weather forecast if you have flexibility in planning your travel time,” Schwingle notes.
Where can we find updates on the colors until fall?
FOX 9 will be posting one to two weekly updates on FOX9.com as peak season approaches to keep you informed and point you in the right direction. FOX 9 will also have an update from the Minnesota DNR with a press conference the first week of September that may provide more details on our leaf color peeping this year.
