Do you have ripe tomatoes on the Fourth of July?

For many Sacramento-area gardeners, Independence Day is the unofficial due date for the first round of ripe tomatoes. If you can harvest your first tomatoes by July 4, you know you’re headed to a good tomato season.

Generally, if you transplanted your tomatoes outside in April, they should be producing mature tomatoes by early July. But variables in weather have made that rule of green thumb less dependable.

Which leads to tomato envy – and lots of questions. Why aren’t my tomatoes ripe? Or, worse, why don’t my vines have any tomatoes?

Farmer Fred Hoffman made note of this conundrum in his current “Beyond the Garden Basics” newsletter.

“Many area gardeners are wondering about the lack of color of their tomatoes now, in mid summer,” observed Hoffman. “Blame the triple-digit heat spikes that have occurred coast to coast for the slowdown this summer.”

Tomatoes like it hot – but not too hot. Temperatures above 95 degrees hamper pollination and ripening.

“Researchers from across the country have studied the effect of excess heat on ripening tomatoes,” Hoffman added. “Their consensus: Don’t worry, be happy. Those tomatoes will still be edible. And if you want to speed up the ripening process, harvest those tomatoes that are beginning to show color before the next forecast triple-digit heatwave hits. Let them ripen indoors, in a dark place on the kitchen counter.”

Other factors may be in play, too, he said. Too much shade or lack of foliage can impede ripening tomatoes.

Hoffman, a lifetime master gardener, cites UC research on tomato fruiting and ripening. No ripe tomatoes in July could be because:

* Nights were too cold (under 55 degrees).

* Days were too hot (over 95 degrees).

* Tomatoes were set out too early (cold soil inhibits growth and development).

* Too much shade; tomatoes need at least six hours of sun daily.

* Too much nitrogen fertilizer; it produces lots of leaves but no tomatoes.

Heirloom varieties tend to be extra fussy, he added. They need just-right conditions in order to produce a good crop.

As for ripening, red pigments in tomatoes don’t form properly when temperatures are regularly above 95 degrees, but yellow and orange pigments do. So yellow and orange tomato varieties can reach their full colorful ripeness on the vine, but red ones need cooler afternoons.