Q: Our plants have *tons* of large green tomatoes, but they won’t ripen on the vine! They’re absolutely gorgeous, non-diseased green tomatoes that get lots of sunshine. Any tricks to make them ripen up?

A: It’s mostly a waiting game. Tomatoes ripen when they get enough sugars and hormones from the leaves to complete the process of maturing. With so many tomatoes on the vine, the leaf surface area has a hard time keeping up with the demands of the fruit.

Heat also explains why fruit stops ripening. Tomatoes stop making the pigments carotene and lycopene at temperatures higher than 85 degrees.

Even though tomatoes are called “full sun” plants, the roots have to be cooler than 80 degrees and the fruit has to be shaded by lots of foliage to keep it cool enough to ripen fully

You can pick green tomatoes when the blossom end is one-third pink and ripen them on a kitchen window.

Tomato and bell pepper color, flavor, plant growth and fruit production are optimal when daily temperatures are 70-75F, with nighttime temperatures 60-65F. High temperatures, specifically anything above 85F during bloom and ripening periods, will result not only in reduced fruit set (bud abort), but fruit flavor, texture and color will also be directly affected.

This “tomato time-out” is mainly due to the plant using most of its resources, like water and nutrients, in addition to its manufactured photosynthetic products, to simply survive temperature extremes. More resources maybe partitioned to produce more roots in an attempt to access more water which causes the plant to suddenly cease to grow. Remember, the plants are attempting sustain all of their physiological processes, like cool its leaf tissues, and continue to grow in order to produce new blooms and new foliage, and also ripen fruit, all at the same time! That requires a huge amount of plant resources and energy !

Tomatoes do not like cooler temperatures either. In fact, temperatures lower than 50F will cause a type of chilling injury. It may take 2-3 days for tomatoes to return to their previous levels of photosynthetic activity, even after just a brief chill period.

See “How a Tomato Ripens”

“It takes about forty to sixty days from the time the tomato flower is fertilized until the fruit reaches full maturity. It attains its full size in about half that time, having accumulated starch all the while. Since the fruit is still grass green, growers call this the “mature green” stage. As the days go by, the green chlorophyll in the fruit is degraded and eventually destroyed as the final yellow or red pigmentation increases. The fruit, now called a “breaker,” has a mottled or streaked appearance. As the tomato ripens to its full color, its acidity decreases, essential oils and other components of its flavor develop, the starch becomes sugar, and the fruit softens.”