You planted tomato plants (maybe even started them from seed) and tended them lovingly with just the right amounts of water and fertilizer. The plants grew beautifully and produced green fruits. You couldn’t wait for them to ripen so you could enjoy that first juicy bite – but those green fruits aren’t turning red. What went wrong?

Tomatoes go through stages on their way to maturity. Once they grow to full size, changes in the pigment cause them to change from green to whatever color is appropriate for the cultivar – red, orange, yellow, purple or pink.

The best temperature for ripening tomatoes is between 70 and 75 degrees. When temperatures are above 85 degrees, like during the recent stretch of hot weather, lycopene and carotene (the pigments responsible for orange or red tomatoes) are not produced and ripening slows or stops completely. There is not much a gardener can do but continue to care for plants and wait for the end of the heat wave.

To prevent overcrowding while waiting for fruits to ripen, pick those showing early signs of ripening (a blush of color), and bring them inside where they can ripen in cooler temperatures. Immature fruit will not ripen. And never put tomatoes in the refrigerator. Cold temperatures rob tomatoes of their flavor as their sugars turn to starch.

Another reason tomatoes may be slow to ripen is an over-abundance of food or water. Once vines have reached the desired size, reduce fertilizer unless the plants are sending signals of nutrient deficiency. Reducing water may encourage plants to ripen their fruit, but also limits the production of more fruit, so save this strategy for the end of the season.

One more suggestion for encouraging tomatoes to ripen is to direct more of the plant’s energy to its fruit. Remove the lower leaves and any foliage that is yellow, and pick some of the smaller, immature fruit. Be sure to harvest any ripened fruit every day.

And remember, if all else fails, you can try fried green tomatoes.

Diana Stoll is a University of Illinois Extension master gardener for Kane County. The “Learning to Grow” column runs weekly during warmer months of the year. Call the extension office at 630-584-6166 for more information. Feedback on this column can be sent to editorial@kcchronicle.com.

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