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What’s wrong with my tomatoes? Probably the heat

Triple-digit temperatures can affect pollination, tomato development

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

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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Garden Checklist for week of Feb. 2

During this stormy week, let the rain soak in while making plans for all the things you’re going to plant soon:

* During rainy weather, turn off the sprinklers. After a good soaking from winter storms, lawns can go at least a week without sprinklers, according to irrigation experts. For an average California home, that week off from watering can save 800 gallons.

* February serves as a wake-up call to gardeners. This month, you can transplant or direct-seed several flowers, including snapdragon, candytuft, lilies, astilbe, larkspur, Shasta and painted daisies, stocks, bleeding heart and coral bells.

* In the vegetable garden, plant Jerusalem artichoke tubers, and strawberry and rhubarb roots.

* Transplant cabbage and its close cousins – broccoli, kale and Brussels sprouts – as well as lettuce (both loose leaf and head).

* Indoors, start peppers, tomatoes and eggplant from seed.

* Plant artichokes, asparagus and horseradish from root divisions.

* Plant potatoes from tubers and onions from sets (small bulbs). The onions will sprout quickly and can be used as green onions in March.

* From seed, plant beets, chard, lettuce, mustard, peas, radishes and turnips.

* Annuals are showing up in nurseries, but wait until the weather warms up a bit before planting. Instead, set out flowering perennials such as columbine and delphinium.

* Plant summer-flowering bulbs including cannas, calla lilies and gladiolus.

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