If your garden tomatoes look like they’ve been placed on hold, you’re not alone! Now it may sound like an easy excuse when we horticulturists blame such things on the weather, but I really think the extreme hot weather we experienced this summer might be the culprit.
Tomato fruits go through several stages of development during their maturation process. During early stages, the fruit continues to grow in size and remains green, typically requiring 40-50 days. Once the fruit has reached full size (called “mature green”), changes in pigment begin to take place, causing the green to fade to light green then to the appropriate pigments for that particular cultivar, be it red, pink, yellow or orange.
Ripening and color development in tomatoes is governed primarily by two factors: temperature and the presence of a naturally occurring hormone called “ethylene.”
The optimum temperature range for ripening mature green tomatoes is 68–77 deg. F. The further temperatures stray from the optimum, the slower the ripening process will be. And, when temperatures are outside the optimum range for extended periods, conditions may become so stressful that the ripening process virtually halts.
At the same time, tomatoes do not produce lycopene and carotene, the pigments responsible for ripe tomato color, when temperatures are above 85 deg. F. So, extended periods of extreme heat cause tomatoes to stop ripening. The resulting fruits often appear yellowish green to yellowish orange.
There’s not much the gardener can do but wait out the weather. As temperatures become more favorable, the ripening process should get back on track, assuming other stresses do not take their toll!
We may still have quite a few more weeks of good growing weather before killing frost; it’s hard to say for sure. But even if frost comes early, keep in mind that tomatoes that have reached at least the mature green stage can be ripened off the vine. Look for a color change to at least a lighter green — and a little bit of blush is even better. Those that are still immature green will never ripen, so save those for the compost pile.
The more green the fruit, the more sensitive it is to chilling injury. Store mature green to slightly blushed fruits at 60-65 deg. F, or warmer if faster ripening is desired. Ripe fruits can be stored cooler, as low as 45 deg. F. The typical home refrigerator is too chilly for storing tomatoes. Instead, pack fruits in shallow layers and keep in a well-aerated location where temperatures can be maintained and progress monitored.