FIMBY: How to help tomatoes thrive on hot days

This is another installment in our Food in My Back Yard series, dedicated to edible gardening.

Tomato weather has arrived in Sacramento. With several days forecast in the upper 80s and even low 90s, expect your vines to soak up that heat and really grow.

But how hot is too hot? That’s the tomato conundrum – tomatoes are temperature-sensitive.

Too cold, they won’t thrive. (If afternoon highs linger below 70 degrees, they’ll barely grow; that’s why Sacramento tomatoes aren’t planted in February.) Too hot, they won’t set fruit. (And what’s the point of all vines and no tomatoes?)

Tomatoes love heat and sun, but there’s a limit. That dividing line is 95 degrees. When temperatures stay above 95 degrees (and we’ll be there soon!), 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 the coming 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.

* Watch for proper pollination. Tomatoes are wind pollinated; no bees necessary. But when temperatures reach 95 degrees (and stay hot), tomato pollen dries out and refuses to “stick.” If your vines are producing plenty of blooms but not actually setting fruit, it may be temperature-related. Pinch off those barren blooms to prompt the plant to send out more flowers. (Then, keep your fingers crossed that we’ll have some cooler afternoons.)

* 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; straw has no seed.)

* Don’t fertilize during a hot spell. Feeding tomatoes on 100-degree days 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.