Effects of a Warm Winter on a Colorful Autumn

What creates good fall foliage?

I was asked back in December by a friend who was getting worried because the mild weather was causing certain trees to bloom. I’ve seen this happen several times over the past years and it seems the trees weather it without a noticeable effect on the fall colors.

I just read an article by the Boston Globe (this was in 2015), and they asked Norm Helie, an applied plant and soil scientist who consults at the Boston Public Garden. He said he has seen this happen during the past three warm winters and the flowers and trees didn’t get hurt by it.

What would hurt is an abrupt freeze which doesn’t allow the trees to prepare for the winter. When we go into winter “very slowly,” the trees can actually build to the unexpected warmth.

Critical factors

There are so many factors that will affect what the New England fall foliage will look like. But here is what I think are the most important ones. The three most critical factors are temperature, precipitation, and amount of daylight. The balance between all of this is usually the best, but nature seems to abhor a balance, and each year is different in relation to:

Precipitation
Temperature
Sunny days

Rain is critical to a good growing season and in my opinion, an optimal year would be a spring that is just a little light on rain which means that we have occasional rainy days but not a week-long drenching. This way the anthracnose fungus will be kept to a minimum come September. Also, if we have average rainfall during the summer then the trees won’t mind a “little drought in the fall. (drought in Sept MAY increase the sugars and this can mean brighter colors)

If the rain diminishes in Sept and doesn’t show in Oct, I would be quite happy. But what we seem to get is a dry Sept and rain every weekend in October. Not what I want to see.

As far as temperature goes I like to see a warm spring and a warm to mildly hot summer (80s – 90s) and in August we usually get a last hot week and then as the month switches to September, the temperature should also start sliding southward. Ideally in September, we would have sunny warm days in the 70s and nighttime temps cooling-off in the 50s. (AND low 40s by mid-Sept dipping to the 30s going into Oct!)

Sunny days are critical for the autumn peak colors. The more days that we have that are bright, the brighter the fall colors. The bright reds are dependent on sunny days over much of September and October. During these two months, I like to see virtually no rain (or very little) with daytime temperatures in the mid-60s to low 70s and evening temperatures approaching the low 30s. We don’t want a hard freeze but a light freeze in the mid-low 30s is perfect for generating bright colors.

Negative critical factors

Anthracnose
Drought
Winter Moth or other pests

Anthracnose is a fungus affecting deciduous trees. It usually doesn’t appear until late August when the first leaves start changing color. read more about it here.

Drought is a tough subject because some dry conditions help the fall colors intensify the sugars and thereby making the fall colors brighter. BUT! too much will stress the trees and cause them to drop their leaves and it also slows the turning of the autumn colors. It’s a fine line to walk.

Winter moth or Asian longhorn beetle are both very real threats to our fall foliage pastime.

Will September set us up for success or failure in our search for fall colors?

In the past, I’ve written many articles about everything from, how to make plans in case of rain or just a lack of ideas on where to go or what to do.

This is why I added several pages of articles to the menus. These pages contain either planning articles or topics of interest (like covered bridges, festivals, train rides, and many others) that I hope will give you ideas of things to do during your fall foliage vacations.

What sorts of fall colors we receive each September and October are a mystery, and while I try to make educated guesses, they will be determined by the weather we receive.

If you have any specific questions, just hit the comments below.

Jeff Foliage Folger

Autumn is a state of mind more than a time of year – Jeff Foliage

Visit my Amazon affiliate store for items that Lisa and I have curated for you. These items are either New England-made or things we think will make your fall foliage trip more successful.