Will Wildfire Smoke Harm Your Outdoor Plants? Here’s What Experts Say

In certain parts of the United States, wildfires and the resulting smoke have been causing air quality warnings and orange, hazy skies once again this summer. Beyond the effects wildfire smoke can have on us, our gardens could also be impacted. We asked experts to explain the potential stress your plants could experience, and to share some easy ways you can protect your garden as those ominous clouds of smoke roll through.

How Wildfire Smoke Affects Gardens

Incoming smoke and ash can stress outdoor plants because these particles scatter light, allowing less to reach leaves directly. When plants receive less sunlight, their photosynthetic process slows down, preventing them from growing as well. Most plants can tolerate a few days of reduced light, but if your area is experiencing thick smoke for more than a week, you may notice your plants looking less healthy.

Because the smoke comes from forest fires, you don’t need to worry too much about the effects of plastics, chemicals, or acid rain on gardens, says Hillary Jufer, the horticulture program manager at Cornell University’s Cooperative Extension program. The most important thing is to minimize stress on your plants as much as you can until the smoke clears.

How to Help Gardens Exposed to Wildfire Smoke

Most well-established trees, shrubs, and perennials will handle a short spell of smoky conditions just fine. But more delicate and fast-growing plants, such as herbs, vegetables, and flowers, may need extra attention. Use these expert tips to minimize smoke damage to them.

Just Add Water

“The simplest thing one can do—whether this is potted plants or plants in the ground—is to make sure that things are well-hydrated during these episodes,” says Anthony Garza, the horticulture and grounds supervisor at the University of California Botanical Garden at Berkeley. “That extra heat and smoke can put stress on that plant.”

Jufer adds that if the weather is also very hot and dry, your container plants will be thirsty. “You might need to water them every day or twice a day,” she says, depending on rainfall.

Rinse and Repeat

You’ll often hear the advice to avoid wetting your plants’ leaves while watering so you don’t encourage diseases to take hold and spread. But if your outdoor plants have collected some dust or ash during a period of heavy smoke, rinsing them off with a hose can be beneficial. This quick wash cleans debris off leaves to allow more light to hit them. Plus it will provide them with a bit more moisture as they bounce back from periods of high stress.

Do your rinsing in the morning. This allows the water to evaporate off the leaves more quickly as the day warms up, which will help minimize diseases. Shower off your plants every couple of days until the smoke has dissipated.

Go Under Cover

“Lessening the stress for your plants with the watering, with the washing down, is probably the most practical thing that most of us could manage,” says Garza. But for edible crops and other plants you want to keep especially sheltered, he suggests using floating row covers or a frost cloth. Usually used to ward off frost and pests, these permeable materials offer a budget-friendly physical barrier against dust and ash too.

Garza cautions that while these covers do let through some light, they may compound the already-low levels of sunlight that plants are exposed to. If kept on too long, this can further impede photosynthesis, adding to problem. Remove the covers as soon as the smoke levels begin to improve.

Add Light

Specifically in a greenhouse, or for indoor plants more affected by a change in sunlight, Garza suggests adding supplemental light with LEDs. You don’t need to bathe all your plants in light, though—Garza says this is best for those more precious, delicate plants in your collection.

• <span>Gardening</span>
• <span>Caring for Your Yard</span>
• <span>Garden Care</span>