Will smoke harm my tomatoes?

The bees don't seem to mind the smoky skies in midtown Sacramento July 3.
(Photo: Debbie Arrington)

California wildfires can affect your vegetable garden; how to cope with smoke and ash

By Debbie Arrington

Smoke from nearby wildfires burns our eyes and lungs.  It's uncomfortable -- and unhealthy -- to be outdoors. But what about our plants? How are our tomatoes coping with hazy skies and clouds of ash? Will those vegetables be safe to eat?

Summer is prime wildfire season in California, and also when local gardeners are most likely harvesting fresh vegetables. This is the start of Yolo County's prime tomato season, too, and wine grapes are maturing throughout the region. 

Current blazes in Rumsey Canyon and Lake County are reminders of how far smoke and ash can travel, many miles from evacuation zones. The after-effects of wildfires became a concern of UC Cooperative Extension master gardeners in Napa and Sonoma counties as well as elsewhere around fire-prone California. After last fall's devastating Wine Country fires, master gardeners researched how to cope with so much ash as well as other issues.

Remember: Take care of yourself first. During smoky weather, try to stay indoors. Sacramento air quality is forecast to be poor as the wildfires continue. Sensitive people should avoid outdoor activity or wear a filtration face mask. Plants deal with smoke better than people. We need oxygen; plants process carbon dioxide.  So they're helping clean that smoke out of the air. (The haze can act like cloud cover and lower temperatures, too. That puts less strain on tomatoes and other summer veggies.)

But smoke also contains particulate matter that clogs leaf stomata (or pores) and hampers this cleansing process. This residue can coat the outside of vegetables and fruit, too. To remove that residue, spray plants with water -- preferably early in the morning. That acts like a rain shower, nature's way of rinsing off that grit.

Grapes and tomatoes can absorb smoke into their skins, causing what's called "smoke taint" to their flavor. (Winemakers refer to it as "ashtray taste.") The volatile phenols in the ash and smoke also are absorbed by the plant's leaves. Research in Australia showed that pressure-washing the vines actually could make the problem worse, although it did help if the leaf canopy was plucked off beforehand (such as shortly before harvest).

Most growers wait and wash the smoke residue off the picked fruit. They also may discard the grape skins before processing. Consider that same approach if processing your own homegrown grapes.

As for the ash, it can cause a gritty film on tomatoes and other vegetables. It tends to stick to tomato skin or kale leaves, more so than ordinary dirt. 

Not all ash is the same. Ash from burning forests or grasslands is similar to fireplace ash; it's acidic, even beneficial to a garden, and generally safe. That ash and any smoky residue could be scrubbed off with water and a little dish soap. then rinsed and dried. For leafy greens, submerge completely in a basin filled with water and a teaspoon of soap, scrub, rinse and pat dry. 

Ash from chemical fires, destroyed buildings or burned-out automobiles can be harmful. Vegetables covered with that ash residue should be discarded, the master gardeners recommended. If working around ash, wear protective clothing such as long sleeves, long pants, gloves, googles and a face mask. If ash gets on your skin, wash off promptly.

One more tip from the master gardeners: Don't use leafblowers for ash removal. It just puts it back into the air.