Q: The wildfire smoke has been thick near my house in Duluth this week. I looked at AQI readings and ours was around 900, way above the hazardous level. Will this smoke settle on my garden vegetables and make them unsafe to eat? Will it affect the plants’ leaves or the soil? Is there anything I should do?
A: That is a good question. The short answer is that your plants are probably fine. They are generally better at dealing with awful air than we humans are. We should definitely refrain from working in our gardens when the air quality is poor. The health hazards of breathing in wildfire smoke are significant. If you must go out to tend to something, wear an N95 mask if the AQI is in the red zone, and limit your time outdoors as much as possible. If the plants have enough water they will likely come through all right.
Wildfire smoke will not generally block enough sunlight to interfere with plants’ ability to photosynthesize. But wildfires can also cause an increase in ozone, which is harmful to both people and plants. Plants that are subjected to damaging concentrations of ozone may not photosynthesize as well, and eventually may show brown patches on the leaves. Yields may be reduced.
MPCA data shows that ozone levels did spike in Minneapolis, Duluth and Ely after lightning sparked multiple fires in mid-July. Presumably other communities were also affected. But ozone damage to plants depends on other factors, too, such as heat, humidity, the sensitivity of the plant and the length of exposure. Our gardens may well be okay. All we can really do is keep an eye on our plants and check them for damage. There are good pictures of plants damaged by ozone in this article from Purdue University at vegcropshotline.org/article/ozone-injury-on-vegetable-plants. If you see what looks like ozone damage to leaves, try to reduce other stressors on the plants. Make sure they are well watered, and don’t fertilize.
It’s okay to eat the produce from your garden even if your neighborhood was choked with wildfire smoke. There is evidence that smoke can affect the flavor of grapes grown for wine making. But grapes are more likely to absorb the chemicals in smoke than the plants we tend to grow in our vegetable gardens. Tomatoes, leafy greens, cucumbers and such should all be fine. Even ash falling on the garden will likely not cause damage, unless it’s heavy.
Once the air clears and you can work outside, you can use a hose to rinse your plants’ leaves. Don’t use a leaf blower to blow away ash. You don’t want to put more fine particles into the air. Rinse any produce you’re gathering outside and then rinse it again inside.
If the ash fall was heavy, or if the smoke and ash came from a structure fire, you will want to take more precautions. Structure fires contain toxins that aren’t present in wildfires. If there’s been a structure fire nearby, it may be a good idea to have a soil test to make sure toxins didn’t accumulate in your garden beds.
Be sure to continue to protect your own health as you clean up your garden. Wash your self and your clothes if you work in areas contaminated with ash.
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