If you’ve noticed trees in Ontario changing colour or shedding leaves far ahead of the fall season, you’re not imagining it. The province’s dry and hot summer has stressed out many trees, prompting them to shut down early as a survival response.
Across southern Ontario, rainfall levels have been well below normal for July, with deficits ranging from 50 to 75 per cent in most areas. This lack of moisture has left trees like maples, birches, and fruit trees with wilted, discoloured, or prematurely falling leaves. According to Dan Sharp, operations manager with Davey Tree Expert Company, the early colour change is often irreversible once it starts. “You can help the tree along, but this season is basically a writeoff. The tree is going to go to sleep and try again next year,” he said.
The stress signs don’t always come in the form of pretty fall foliage. On species like oaks and birches, yellowing or browning leaves are more common. In some cases, trees overproduce seeds or fruit—such as an abundance of maple keys or apples—as a last-ditch effort to reproduce before shutting down. Oak trees, however, naturally undergo “mast years” where they collectively produce large quantities of acorns every few years, for reasons still not fully understood.
While evergreens are typically more drought-tolerant, even some Scots pines and cedars are showing signs of distress. Scots pines are facing a range of attacks from different stressors, and cedars are sensitive to ongoing dry conditions, as they continuously pull water from the ground.
Sharp points out that when a single tree in a neighbourhood shows early colour change, it may indicate a more localized issue—often soil compaction. Compacted soil restricts oxygen flow to the roots, reduces water absorption, and can take decades to naturally correct. A simple test is to try inserting a screwdriver into the soil; if it doesn’t go in easily, the soil is likely compacted.
Root health is another factor, especially for boulevard trees planted near roadways, where limited growing space can exacerbate stress. Some trees may still be reeling from last summer’s heavy rains, which caused root rot in waterlogged soil. This year, fast-moving rain has done little to replenish deep root moisture.
In addition to environmental stress, trees in poor condition are more vulnerable to pests and diseases. Insects and fungal pathogens often attack already weakened trees, much like illnesses strike people with compromised immune systems.
To support your trees, Sharp recommends mulching around the base. Mulch helps retain moisture, slowly decompacts the soil, and encourages beneficial organisms like earthworms and microbes. It also provides a physical barrier to protect tree roots from foot and vehicle traffic. Over time, as mulch decomposes, it naturally enriches the soil—mimicking the forest floor.
Proper watering is also key. Unlike lawns that benefit from short, daily watering, trees need a deep soak once a week. Sharp suggests watering for about an hour to ensure moisture reaches 10 to 16 inches below the surface. For evergreens, a soaker hose laid beneath the hedge and left running for an hour weekly is ideal.
While pruning bare branches may not offer much help unless there’s disease, some slow-release fertilizer—formulated specifically for trees—can assist. Sharp warns against using high-nitrogen lawn fertilizers, which can trigger erratic and unhealthy growth.
Ontario’s early fall-like landscape may be alarming, but understanding the causes—from drought and soil issues to natural stress responses—can help homeowners better care for their trees in this challenging climate.