As wildfire smoke from Canadian fires continues to affect air quality across Southeast Michigan, a lot of homeowners are asking the same question: what does this mean for their landscape plants? Smoke from Canadian wildfires has led to unhealthy air quality across much of the state, with Detroit registering among the worst air quality in the world during some recent episodes.
We naturally focus on protecting ourselves and our families during these events, but garden plants are dealing with the smoky conditions too. The good news is that most landscape plants are surprisingly resilient — though there are real considerations for Southeast Michigan gardeners.
The current wildfire smoke situation in Michigan
The Michigan Department of Environment, Great Lakes, and Energy (EGLE) has issued air quality advisories tied to elevated fine particulate levels statewide, driven by ongoing Canadian wildfires. Smoke from fires in Canada — including one that forced evacuation orders for the roughly 5,000 residents of Flin Flon, Manitoba — has been drifting southward into the Great Lakes region.
It's too early to say whether Michigan will see the scale of smoke that hit the state and the western U.S. in past years, but the pattern of smoke events reaching our region appears to be continuing.
How wildfire smoke affects landscape plants: the complex reality
Wildfire smoke has both positive and negative effects on plants, which makes the overall impact more nuanced than you might expect.
The positive effects
Research has turned up some unexpected benefits. In one set of measurements, total sunlight available to plants for photosynthesis dropped only slightly during a smoke event — by about 4% compared to the previous summer — because the smoke scattered light rather than blocking it, increasing diffuse light by roughly a third.
That scattering effect lets sunlight penetrate more deeply into a plant's canopy than it normally would. Diffuse light can reach more of the photosynthesizing leaves throughout the canopy, which can actually help some plants use light more efficiently during a smoke event.
The negative effects
For most landscape plants, though, the downsides outweigh the upsides. Even short-term exposure — 20 minutes or less — can reduce photosynthesis by as much as 50%. Smoke breaks down chlorophyll, the pigment that gives plants their green color and drives how they capture energy from the sun.
The small particulate matter tracked by the Air Quality Index can also get into a plant's stomata — the microscopic openings on leaves that plants use to take in carbon dioxide and release oxygen. When those openings clog, plants effectively start to choke, and can suffer or die if exposure is severe enough.
Compounds in wildfire smoke can also react in the atmosphere over time, changing composition and potentially becoming more toxic. Ground-level ozone formation is a particular concern — it interferes with photosynthesis and damages plant tissue at the cellular level, speeding up senescence.
What about ash on your plants?
Many Southeast Michigan residents have noticed ash on their landscape plants during recent smoke events. Most of it is wood ash from burned trees, and it can act as a kind of mulch — it's loaded with potassium, phosphorus, calcium, and other minerals.
That ash adds nutrients to the soil, including calcium, potassium, and magnesium. Some vegetables — lettuce, asparagus, leeks, garlic, and chives — along with stone fruit like peaches and plums, tend to appreciate the extra boost.
The problem is when the ash gets too thick. It can smother a garden, and especially a lawn — grass isn't built to push up through a heavy layer the way a tree is, so enough accumulated ash can cover the grass entirely.
Caring for your landscape during smoke events
Increase watering. The simplest thing you can do — whether it's potted plants or plants in the ground — is make sure everything stays well hydrated during a smoke episode. Heat and smoke particles together add real stress to a plant.
Clean gently. Wash smoke residue off plants with a gentle hose spray, then give them a long, slow drink to help rehydrate. Work from the top down to the roots.
Skip overhead watering when ash is present. Watering from above leaves residual moisture on the leaves that makes ash stick. Focus on watering at soil level instead when there's visible ash.
Post-smoke recovery
Don't rush to fertilize. Wait until the air clears and plants have had a chance to recover from the stress before adding nutrients.
Rinse weekly. At least once a week, rinse leaves with the hose — top and underneath — to clean off lingering particles.
Add protective mulch. A layer of mulch helps protect the roots of trees, shrubs, flowers, and vegetables from absorbing anything lingering in the air.
Monitor for damage. Watch for leaf discoloration, early leaf drop, or reduced growth. Plants can lose some color or drop leaves if smoke hangs around densely for an extended period.
Which plants are most vulnerable?
Plants that are already stressed, or that need a lot of daily sunlight, are most at risk during a smoke event — shade-tolerant plants handle the dip in light better. In Southeast Michigan landscapes, pay particular attention to sun-loving perennials and annuals, vegetable gardens, young or recently transplanted trees and shrubs, and any plants already stressed by drought or disease.
Food safety considerations
If you're growing edible plants and ash has fallen on your garden, wash produce multiple times before eating it, and trust your nose — if fruit or vegetables still smell like smoke after multiple washes, don't eat them. In general, smoke and ash don't penetrate deep into produce, and peeling skins or removing outer leaves is an extra safeguard.
When to call the professionals
If you notice significant stress in your landscape following a smoke event — extensive leaf drop, browning, or stunted growth — it may be time to bring in a landscaping professional. A certified arborist or lawn care technician can assess whether your plants are struggling from a bout with wildfire smoke and recommend next steps.