I have attached a fact sheet which helps identify various problems that tomatoes may have. If you aren’t seeing any of these, it could just be the extreme heat we have been experiencing.

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.