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What’s wrong with my tomatoes? Probably the heat

Triple-digit temperatures can affect pollination, tomato development

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED JUN 21, 2024

Extreme heat shuts down production in tomato plants: pollen dries up and the flowers won't set fruit. Kathy Morrison

High heat is on its way – and that’s bound to affect our tomatoes.

First this update from the National Weather Service: Saturday is going to be hot!

A heat advisory is in effect from 11 a.m. to 8 p.m. Saturday, June 22, says the weather service.

“High temperatures 100 to 107 expected. Limited overnight relief with low temperatures in the mid 60s to mid 70s.”

The areas expected to be hardest hit include central Sacramento Valley, Mother Lode, northern Sacramento Valley, northern San Joaquin Valley and southern Sacramento Valley, says the advisory. The warmest overnight temperatures will be in the northern and central Sacramento Valley and foothills.

Saturday’s high temperature in downtown Sacramento is expected to reach 103, says the weather service. That’s 15 degrees above normal.

Be prepared to keep the A.C. running all night. Stay hydrated. Bring pets indoors.

But we can’t bring our vegetable gardens indoors. They have to cope where they’re planted.

So concentrate on keeping them comfortable. Water deeply in the morning before the heat arrives. Make sure there’s mulch (straw, leaves, wood chips, etc.) to help retain that moisture and keep roots cool. Erect some temporary shade (such as an umbrella or shade cloth) over peppers and tender transplants.

Tomatoes and large-leaved vegetables such as squash tend to wilt in the afternoon; that’s a normal coping mechanism. If they’re still wilted in the morning, they need a drink.

Speaking of tomatoes, the top issue right now is lack of pollination. Plants have blooms, but they drop off before they form fruit.

That’s related to heat, too. Tomato flowers won’t set when temperatures stay high – over 90 degrees – for prolonged periods. The pollen dries out. But indeterminate varieties will produce more flowers with new growth.

Tomatoes like some heat; days between 80 and 90 degrees produce optimum growth, according to UC research. But flowers will not set on 100-degree days.

Heat isn’t the only weather factor that can affect tomato pollination. Lack of wind or breeze also can affect tomato set. Tomatoes generally are wind-pollinated. To help with pollination, gently wiggle the tomato’s cage or trellis to shake up and spread the pollen.

For more advice on tomatoes and other summer crops, check out the UC IPM website: https://ipm.ucanr.edu/.

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tomatoes weather summer June pollen heat Sacramento gardening vegetables pollination triple-digit temperatures summer vegetables

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Garden checklist for week of May 10

Take it easy during that high heat – then get to work! Your garden is calling.

* Remember to irrigate your tender transplants. Seedlings need consistent moisture. Deep watering will help build strong roots and healthy plants. Water early in the morning for best results.

* Plant, plant, plant! It’s prime planting season in the Sacramento area. Time to set out those tomato transplants along with peppers and eggplants. Pinch off any flowers on new transplants to make them concentrate on establishing roots instead of setting premature fruit.

* Direct-seed melons, cucumbers, summer squash, corn, radishes, pumpkins and annual herbs such as basil.

* Harvest cabbage, lettuce, peas and green onions.

* In the flower garden, direct-seed sunflowers, cosmos, salvia, zinnias, marigolds, celosia and asters. (You also can transplant seedlings for many of the same flowers.)

* Plant dahlia tubers. Other perennials to set out include verbena, coreopsis, coneflower and astilbe.

* Transplant petunias, marigolds and perennial flowers such as astilbe, columbine, coneflowers, coreopsis, dahlias, rudbeckia and verbena.

* Keep an eye out for slugs, snails, earwigs and aphids that want to dine on tender new growth.

* Feed summer bloomers with a balanced fertilizer.

* For continued bloom, cut off spent flowers on roses as well as other flowering plants.

* Put your veggie garden on a regular diet. Set up a monthly feeding program, and keep track on your calendar. Make sure to water your garden before applying any fertilizer to prevent “burning” your plants.

* As spring-flowering shrubs finish blooming, give them a little pruning to shape them, removing old and dead wood. Lightly trim azaleas, fuchsias and marguerites for bushier plants.

* Don’t forget to weed! Those invaders are growing fast.

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