This has not been a great year for tomatoes in my garden and from what I hear, I’m not alone. Since they’re heat lovers, I would have thought the plants would revel in the scorching temperatures of late July. But I’ve recently read that heat isn’t the key to ripening. In a regional update, Dr. Steve Reiners of Cornell University Capital District Vegetable & Small Fruit Program, says that the “…optimum temperature for ripening tomatoes is 70 to 75 F.” and temperatures in excess of 85 F causes ripening to slow – apparently to a crawl. The red pigments in tomatoes are caused by carotene and lycopene and at high temperatures, tomatoes stop producing them. Go figure!
So my tomatoes are pouting. And since we’ve had such a wet and humid season, they are also spotting and sprouting all kinds of fungal disease. I tried Spinosad this year, but it doesn’t seem to work as well as copper or sulfur, as a preventative.
Dr. Reiners says exposure to sunlight has nothing to do with ripening tomatoes and can have the opposite results, because more sunlight means more heat. So don’t try the old trick of trimming away leaves and branches. That will just lead to sun scald.
What can we do? Well we could learn some patience, I guess, but what’s the chance of that happening? At this point in the season, whatever fruits were going to form, pretty much have. Pinching the remaining flowers off the vine will allow it to focus on ripening the fruit that is already set. If that’s too drastic for you, at least pinch a few.
Or you can take matters into your own hands and harvest any fruits showing a blush of color on their blossom end and bring them indoors, to finish ripening. Place them in paper bags with an apple. The ethylene gas given off by the apple will speed the ripening process. They’ll still taste summer fresh.
Source: Why Aren’t My Tomatoes Ripening?