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How to save your plants during a heat wave

Soil moisture is key to survival in triple-digit temperatures

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED AUG 16, 2022

Spraying tomato plants with water early in the

morning helps fight spider mites and aphids while

refreshing the leaves and raising the humidity

around the plants. The runoff helps the plants, too.

(Photos: Kathy Morrison)

As the weather forecasters like to say: We’re having a heat wave!

Triple-digit days dominate our Sacramento forecast at least through Saturday. In its Excessive Heat advisory, the National Weather Service warns, “Drink plenty of water; don’t wait until you’re thirsty.”

That same advice applies to your garden. Plants with roots in soil that stays evenly moist – not soggy – have the best chance of surviving, even thriving during this heat wave.

The secret is to keep the soil from completely drying out – not on top, but down 4 to 6 inches in the root zone. Use a moisture meter to check. Or use a long-handled screwdriver; if you can’t shove it in 6 inches, you need to irrigate.

Potted plants in containers are especially at risk. The rootball contracts as it dries out, leaving gaps around the sides of the pot. When you pour water on a severely dry potted plant, the water tends to run out the sides without ever penetrating the rootball. In such cases, you may need to submerge the pot in water, let soak for a few minutes, then drain. Don’t let the roots sit in standing water; they’ll suffocate.

Wilting in the heat of the afternoon is normal for many plants, especially those with big thin leaves such as hydrangeas or squash. But if plants are wilted in the morning, water immediately.

Burlap or shade cloth can help prevent sunburn

on tomatoes or other summer vegetables.

Are there brown spots on your peppers or bleached-out areas on tomatoes? For plants showing signs of sunburn, erect temporary shade. This can be as simple as draping some cloth (burlap, sheeting, etc.) over a trellis or tomato cage.

Spider mites in particular are loving this heat; this itty-bitty arachnid thrives in hot and dusty conditions. If you see wispy webs covering leaves and stems of shrubs and other plants, knock them down with a strong stream of water from the hose.

This summer shower destroys their webs and washes the mites and dirt off the plants. It also disrupts what attracted the mites in the first place – dry, dusty leaves.

Wash mites off plants early in the morning, so the plant’s foliage has all day to dry. Fungal diseases usually aren’t a problem right now; powdery mildew can’t stand anything above 90 degrees.

This same approach also works against aphids. Showering plants is not wasting water; the runoff will go to the plant’s roots. Most plants also absorb moisture via their foliage.

Avoid spraying neem oil or other treatments (often recommended for pest control). The oil coats the plant’s foliage and increases its sensitivity to extreme heat. Instead of helping the plant, the oil “cooks” its tender leaves.

And put off any fertilization until weather cools back to normal. Feeding increases a plant’s water needs. During this heat, it just adds to plant stress.

For more on heat stress and plants, check out this advice from the UC Integrated Pest Management Program: http://ipm.ucanr.edu/PMG/GARDEN/ENVIRON/thermal.html .

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Keywords:

Sacramento heat wave soil moisture irrigation gardening integrated pest management heat summer vegetables heat damage triple-digit temperatures UC IPM summer August

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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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