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Smoke and high heat? Watch out for ash, ozone damage

Triple-digit temperatures and smoky conditions can create high pollutant levels

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED JUL 23, 2024

Ash collects on the leaves of a large lily plant. Debbie Arrington

Maybe consider wearing a facemask while gardening?

Ash on the leaves of plants is a reminder: With wildfire smoke comes fine particulate matter. That stuff can get in your lungs – as well as clog plant pores.

So far this wildfire season, we’ve been relatively lucky in Sacramento; our air quality has remained “moderate” to “unhealthy for sensitive people” instead of downright unhealthy for everyone.

We already have unhealthy heat; the National Weather Services issued a “heat advisory” for the Sacramento region through Wednesday night with highs of 107 to 112 degrees possible.

Triple-digit heat coupled with wildfire smoke can create another problem for plants: Ozone damage. It starts out as stippling – little dots all over large leaves. Or parts of leaves or petals may look like they were sun-bleached white or silver.

Ozone is what happens when wildfire ash and other pollutants get “cooked” by temperatures more than 100 degrees. It makes our eyes water and throats hurt. (Think of a real smoggy day.)

While ozone high up in the atmosphere is a good thing, ground-level ozone can be very bad. In Sacramento’s case, it can be created by a combination of wildfire ash and other pollutants (usually nitrogen oxides and volatile organic compounds), intensified by bright sunlight and triple-digit heat.

Ground-level ozone can prevent a plant's leaves from properly doing their job. Ozone enters the leaf's stomata and burns the leaf's tissue.

Signs of ozone damage include dark stippling and bleaching of foliage. Plants lose their vigor and stop blooming or yielding fruit. Ozone damage weakens the plant and makes it much more susceptible to pests and disease.

Some plants are more prone to ozone damage than others. Researchers at the National Park Service surveyed plants in national parks and found hundreds of species with ozone sensitivity, ranging from asters to elderberries, sycamores and yarrow. Various maple, cherry, poplar and plum trees are all on the ozone-sensitive list.

In the meantime, tackle the ash and heat with the same remedy – water. Keep plants hydrated. Wash ash and soot from leaves. And look forward to lower temperatures later this week; more normal temperatures will not only bring some relief from the heat but reduce the change of ozone damage.

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Keywords:

smoke fires ash ozone trees plants leaves damage Sacramento gardening summer July heat weather National Park Service National Weather Service

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Garden checklist for week of Aug. 16

During this break in the heat, feed your garden. Make sure to water before and after applying fertilizer.

* In the garden, direct seed beets, carrots, leaf lettuce and turnips.

* Plant potatoes.

* Harvest tomatoes, beans, squash, pepper and eggplants to prompt plants to keep producing. Give your plants a deep watering twice a week, more if planted in containers. Also, give them a boost with phosphate-rich fertilizer to help fruiting.

* Watch out for caterpillars and hornworms in the vegetable garden. They can strip a plant bare in one day. Pick them off plants by hand in early morning or late afternoon.

* Feed citrus trees their last round of fertilizer for the year. This will give a boost to the fruit that’s still small.

* Mulch can be your garden’s best friend – it conserves moisture while blocking out weeds. But don't let mulch mound around stalks, stems or trunks. That can promote rot.

* Camellia leaves looking a little yellow? Give them some chelated iron. That goes for azaleas and gardenias, too.

* Pick up after your fruit trees. Clean up debris and dropped fruit; this cuts down on insects and prevents the spread of brown rot. Then feed fruit trees with slow-release fertilizer for better production for next year.

* To prolong bloom into fall, feed begonias, fuchsias and container plants. Always water before fertilizing.

* Fertilize fall-blooming perennials, too. Chrysanthemums can be fed until the buds start to open.

* Prepare for a fall full of flowers by paying a little extra attention to your garden. Cut off spent blooms from roses, annuals and perennials, then give them a boost of fertilizer. Make sure to water plants before feeding. Roses will rebloom about six to eight weeks after deadheading.

* Indoors, start seedlings for fall vegetable planting, including bunching onion, cabbage, broccoli, cauliflower, kale, radicchio and lettuce.

* Sow seeds of perennials in pots for fall planting including yarrow, coneflower and salvia.

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