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Hot tomato! How to help your vines during high heat

Surviving triple-digit temps comes down to moisture and mulch

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Container tomatoes, like this Orange Pixie, should be watered frequently during high temperatures. The soil can dry out much quicker than for in-ground tomatoes. (Photo: Kathy Morrison)

Tomatoes love heat and sun, but how much is too much?

Prolonged triple-digit heat waves can toast tomatoes and other sun-loving crops. Tomatoes in particular tend to be temperature sensitive.

When temperatures stay above 95 degrees, tomato flowers may drop off or refuse to set fruit. Leaves can fry and turn crispy. Ripening tomatoes may split or develop calluses.

Give your vines a hand – along with enough water and shade – to cope with this week’s heat. This advice comes from UC Cooperative Extension master gardeners as well as longtime local tomato growers.

* Water early and deep. Irrigate your tomatoes in the morning, making sure water reaches down at least 6 inches into the soil. How do you know? Test the soil with a probe or long screwdriver; it should easily plunge into the soil. Or use a trowel, dig down and look.

* During hot weather, water tomatoes two to three times a week. Tomatoes normally wilt during a hot afternoon; that’s OK. But if they’re wilted in the morning, water immediately. (Note: A few heirloom varieties, particularly of Russian origin, have a natural tendency to wilt all the time. But if you are growing one of these, you've probably noticed this already.)

* Tomatoes planted in containers may need extra water every day during hot weather. Their potting soil tends to dry out faster.

* Keep watering consistent and don’t let soil dry out completely. That can lead to blossom end rot, the hard brown callus on the flower end of a tomato.

* Mulch is your friend. Make sure your vines have at least 2 to 4 inches around them to help keep roots cool and soil evenly moist. Straw, leaves or shredded bark make the best tomato mulch. Many gardeners prefer straw (not hay) because its light color reflects intense sun rays instead of absorbing that added heat. (Also, hay contains seeds that can sprout and suck nutrients out of soil.)

* Don’t fertilize during a hot spell. Feeding now just puts more stress on the plant.

* Tomatoes love sun, but they can get sunburned. If leaves or developing fruit look bleached out or burned, give your vine some afternoon shade. Erect a temporary shade structure by draping burlap or shade cloth over the tomato cage or trellis. This also helps prevent fruit from cracking.

* If foliage turns brown, leave the dead leaves in place for now. They help protect the fruit from sunburn. After the heat has subsided, prune off the completely dead leaves so new foliage can grow.

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Garden Checklist for week of July 7

Take care of garden chores early in the morning, concentrating on watering. We’re still in survival mode until this heat wave breaks.

* Keep your vegetable garden watered, mulched and weeded. Water before 8 a.m. to conserve moisture.

* Prevent sunburn; provide temporary shade for tomatoes, peppers, eggplant, melons, squash and other crops with “sensitive” skin.

* Hold off on feeding plants until temperatures cool back down to “normal” range. That means daytime highs in the low to mid 90s.

* Don’t let tomatoes wilt or dry out completely. Give tomatoes a deep watering two to three times a week. Harvest vegetables promptly to encourage plants to produce more.

* Squash especially tends to grow rapidly in hot weather. Keep an eye on zucchini.

* Some weeds thrive in hot weather. Whack them before they go to seed.

* Pinch back chrysanthemums for bushy plants and more flowers in September.

* Harvest tomatoes, squash, peppers and eggplant. Prompt picking will help keep plants producing.

* Remove spent flowers from roses, daylilies and other bloomers as they finish flowering.

* Pinch off blooms from basil so the plant will grow more leaves.

* Cut back lavender after flowering to promote a second bloom.

* One good thing about hot days: Most lawns stop growing when temperatures top 95 degrees. Keep mower blades set on high.

* Once the weather cools down a little, it’s not too late to add a splash of color. Plant petunias, snapdragons, zinnias and marigolds.

* After the heat wave, plant corn, pumpkins, radishes, winter squash and sunflowers. Make sure the seeds stay hydrated.

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