If you’ve noticed Toronto’s trees trading green for gold weeks ahead of schedule, you’re not imagining things. Across the city, leaves are changing colour as early as July — a full two months before the typical peak season — and forestry experts say it’s a sign of environmental stress.
Sean Thomas, a forestry professor at the University of Toronto, says the early change is primarily caused by high temperatures and lack of rainfall, which accelerate water loss through tree leaves. When roots can’t keep up, certain sections of the tree — usually the outer crown — respond by shutting down, causing localized leaf dieback and early colour changes.
“It’s a common response to drought conditions,” Thomas said, noting that even small dry patches in the soil can affect individual branches. Other factors like squirrel damage can contribute, but extreme heat worsens the problem.
Marcus Maddalena of Ontario Nature says early leaf drop is a normal survival response, but climate change is making droughts more frequent and severe. “If you see drought in successive years, it can ultimately lead to some of these trees dying,” he warned.
Some species are more vulnerable than others. Sugar maples struggle in drought, while honey locusts and Kentucky coffeetrees — which the city is now planting more of — are more resilient. Toronto is also experimenting with soil treatments like biofertilizers and biochar on hundreds of trees to boost drought resistance.
Normally, Torontonians expect peak fall colour in October, though recent years have seen shifts in both directions, with some seasons delayed into November. Thomas says the “perfect recipe” for brilliant foliage requires steady moisture, sunny days, and cool nights just above freezing.
The City of Toronto is currently inviting residents to weigh in on tree protection bylaws through an online survey open until September 24, as part of efforts to strengthen urban forestry and prepare for climate impacts.