What’s wrong with my tomatoes? Probably the heat

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/.