Ontario's fall colours hang in the balance: Brilliant or browning?

Folks who look forward to taking scenic, daytime trips to parks or trails across Ontario every fall to catch the beautiful leaf colours that the season usually provides...may be disappointed this year.

Well, it depends on a number of factors, including location and weather, but a picture-perfect fall foliage certainly isn't a grand slam this year. You can certainly blame the weather on this disappointment, if the fall colours come up lacklustre this year.

Visit our Complete Guide to Fall 2025 for an in-depth look at the Fall Forecast, tips to plan for it and much more!

File photo. (Calvin Hanson/Submitted to The Weather Network)

Southern Ontario has had a predominantly hot and dry summer, but has seen some rainfall and cooler weather in recent weeks. Northern Ontario, though, has had a contrasting summer pattern, featuring wet weather at times because of the storm track.

However, will those conditions be sufficient enough to give us a picturesque fall foliage this year?

Ontario fall foliage recipe

The good news is that most of Ontario parks are still in the early stages of fall foliage, as of Sept. 9, with a few that are slightly more advanced than others.

Below you will find a graphic that list all of the ingredients for brilliant fall colours. It is nature's recipe, if you will.

Regional outlook

• Northern Ontario: Healthier tree canopies and cooler nights support a vibrant, longer-lasting display.

• Central Ontario (Algonquin, Muskoka, Kawarthas): This region will likely be the sweet spot for vivid colours, with near-ideal conditions and a lack of significant drought in Algonquin and Muskoka. The Kawarthas, however, sit in Ontario’s drought zone, meaning a more muted and shorter-lived display is possible.

• Southern Ontario (Greater Toronto Area (GTA)-Niagara-southwest): This is where things could get tricky. A drier backdrop this season may sharpen some colours, but we're risking a shorter, patchier season if stress persists.

Factors at play in Ontario this year

Adequate summer rain: The foundation

Northern Ontario entered September with a surplus of rainfall, helping to improve the health of tree canopies. By contrast, much of southern and eastern Ontario dealt with pockets of drought by mid-to-late summer.

Tree biologists note that drought-stressed trees often lack the energy to produce the red pigments (anthocyanins) that make the maples and oaks so eye-popping, leading to browning or a premature leaf drop.

Warm, sunny days: The sweetener

Although there was a significant shot of chillier air during the first week of September across northern Ontario, it’s not reflective of the remainder of September. Ample sunny days are still fuelling photosynthesis. That produces sugar in the leaves, which later drives the intensity of reds and purples when the nights cool later in the season.

Cool, frost-free nights: The lock

Apart from a handful of frost advisories in Algonquin and northern Ontario, persistent frost has been absent.

A big chunk of southern Ontario is expected to remain frost-free through September. A hard frost (with temperatures below -2 C) would damage leaves, cutting the season short and leading to browning. This means sugars can stay locked in leaves, helping the colours build gradually.

Dry, early Fall: The finishing touch

Most of Ontario is trending below normal precipitation-wise this month, except for pockets of northern Ontario. A little dryness can enhance colour contrasts, but prolonged stress increases the risk of muted tones and earlier leaf drop. Arborists note that the repeat of hot, dry summers also can weaken trees long-term, leaving them more susceptible to pests and disease.

Shorter days: The master switch

Consider this like a tree’s circadian rhythm.

As daylight decreases, chlorophyll production shuts down and breaks apart, revealing yellows and oranges. Meanwhile, sugars trapped in the leaves fuel the reds and purples. This universal trigger cascades Ontario’s forests into a (hopefully) vibrant display.

When do leaves generally change colours?

The fall colour season can start as early as August sometimes, but it's typically in late September and early October, said Megan Birrell, tourism marketing development specialist with Ontario Parks, in an interview with The Weather Network in 2023.

File photo. (Kitty Yip/Submitted to The Weather Network)

“If you have that consistent temperature, you will see a longer fall colour period. That could be a week or more than a week. If we have [those] consistent warm days and cool nights, we will see a longer fall season,” said Birrell.

Leaves will go through stages in the colour-change sequence, according to Ingo Ensminger, associate professor and researcher at the University of Toronto Mississauga (UTM).

During the summer, there comes a time when most trees "actually" sense a change is coming in the day length, triggering a series of initial steps for the colour modification, regardless of the temperature, Ensminger told The Weather Network in 2023.

(Unsplash)

In terms of timing and how long it takes, Birrell said it depends on the tree type.

"The different types of trees change colours at different times during the season and for different durations. Those iconic red maple leaves that we kind of look for every single year come earlier in the season," said Birrell. "They are really dependent on that time of day."

After those red and orange colours peak, we see leaves on trees such as birch, poplars and Tamarix change to a yellow-gold hue, typically after the maple leaf season, referred to as a golden encore, she said.

Why do leaves change colour?

Ensminger said the main triggers behind the changing of the leaves are temperatures and day length, which determine when the colours actually switch.

We have to understand that it is a procedure that is "highly regulated" by the trees, no matter what species they are.

(Scott/Submitted to The Weather Network)

"The purpose of the changing colours is the tree is preparing for the winter season," said Ensminger. "The change in colour actually indicates that the tree starts to retrieve all the nutrients from the leaves, which means everything that is vaguely useful for the tree is broken down into smaller products."

After all the "nice colours have disappeared," what remains of the leaf is basically a skeleton of the tree, Ensminger said.

"The tree makes a lot of use of the environmental information like temperature and day length, and day length doesn't change at all," said Ensminger.

Stay tuned to The Weather Network as we continue to check in on the progression of Ontario's fall foliage.