How will wildfire smoke affect my garden?

Normally the bees handle pollination.

Zucchini that refuses to grow, wine grapes that taste like a wet ashtray 

By Debbie Arrington

We know how smoky air makes us feel. But what’s happening in our gardens?

Recent California wildfires have choked our skies with sometimes sun-obscuring particulate matter. All that smoke is bad for us mammals. When air quality is so bad, it’s recommended for people and pets to stay indoors.

Plants deal much better with excess carbon. They help filter the bad air and pump out fresh oxygen.

But gardeners may see some aftereffects of too much smoke, in particular zucchini that never grow.

The baby squash starts out OK, but never develops. It rots before it reaches 4 or 5 inches long.

The Brits call it “courgette rot,” referring to the English name for zucchini. It’s due to insufficient pollination.

While skies are smoky, bees return to the safety of their hives. They’re not out, working the squash blossoms, as they normally would do on a summer’s day.

Extreme heat further complicates bees’ lives. If temperatures top 100 degrees (common in Sacramento), worker bees need to bring water back to their hives, from one quart to a gallon a day. Who has time for squash?

So, female zucchini blossoms – which start forming baby squash before the bees arrive – never get the attention they need from pollinators. Without proper pollination, the squash rot before they mature. This issue can happen to other cucurbits as well.

It differs from blossom end rot, a side effect of inconsistent irrigation – such as allowing soil to go completely dry before watering. Often seen in tomatoes and peppers, blossom end rot forms a brown spot or hard callus on the squash tip. Although not pretty, the squash keeps trying to grow instead of rotting away in its youth.

In these hot and smoky conditions, tomato blossoms also will dry out and whither before forming fruit, due to that combination of excess heat and lack of visitors.

Once the smoke clears, bees should be back in action. In the meantime, you can give them a hand.

Take a little paintbrush, such as a watercolor brush. Dip the brush into the male flower (with no swelling at the base) and wiggle it around to collect pollen. Then, put that pollen-covered brush into a female flower (with the swelling at the base) and give it a gentle shake. That replicates how the bees pollinate and may help those baby zucchini survive these smoky days.

As for eating mature squash, tomatoes, peppers, peaches, grapes and other produce that you may be harvesting, wash produce thoroughly to remove any soot. Peel if the skin feels gritty.

What crop suffers the most from smoke? Wine grapes.

Wine grapes can be affected by smoke.

Continued exposure to wildfire smoke is of major concern to California grape growers. Grapes can absorb smoky flavors, developing what’s called smoke taint. That can ruin wine grapes; experts describe its flavor as “burnt, medicinal, campfire … like licking a wet ashtray,” according to The Wine Spectator. Often not apparent in fresh grapes, those bad flavors are brought out by fermentation.

Researchers at UC Davis are working on this issue, including how to predict which grapes may be smoke tainted and ways to cope with it. The good news so far: Smoke taint doesn’t stay in the vines. The next crop will be fine – if it can avoid wildfires.