Tomatoes are a favorite in the garden, but sometimes, they refuse to ripen on the vine. This can be due to cold temperatures, disease, or extreme heat that may signal the end of the growing season. This article explains the science behind tomato ripening and provides practical solutions for turning those green tomatoes red, even when it’s too cold or hot outside.
The Science Behind Tomato Ripening
Tomatoes are warm-weather crops, and their ripening process is significantly influenced by temperature. When the weather gets cold, the enzymes responsible for breaking down chlorophyll and converting other pigments to give the tomato its red color slow down or stop working altogether.
This is why tomatoes don’t ripen in cold weather. They need warmth to activate these enzymes and kick-start the ripening process.
On the other hand, if it’s too hot, tomatoes may overripe, become mushy, and lose their flavor. Sunscald and sunburn are also common during extreme heat in a hot summer climate.
During the daytime, tomatoes thrive in temperatures between 70°F (21°C) and 85°F (29°C). At night, the temperature should ideally be between 60°F (15°C) and 70°F (21°C) for optimal growth.1
Temperatures above 90°F (32°C) during the day and above 70°F (21°C) at night can negatively impact tomato growth and productivity.2
4 Solutions for Ripening Tomatoes in Cold (and Hot) Weather
1. Topping the Plants to Ripen Tomatoes
Topping involves cutting off the top of the tomato plant a few weeks before the first expected frost or end of the season. This stops the plant from producing new flowers and redirects its energy towards ripening the existing fruits.
2. Reducing Watering to Turn Green Tomatoes Red
By reducing watering, you’re stressing the plant slightly, which can stimulate it to ripen its fruit faster. Be careful not to overdo it, though, as too much stress can harm the plant. Learn more about how to grow tomatoes in this blog post.
3. Using Row Covers and Shade
When nighttime temperatures go below 60°F (15°C), row covers can provide additional warmth to your plants, protecting them from frost and helping them ripen their fruit.
Once daytime temperatures are above 90°F (32°C), providing shade can cool the soil and the temperature around the plants. This allows the plant additional time to ripen before becoming too hot.
4. Bring the Tomatoes Indoors to Turn Green Tomatoes Red
If freezing temperatures are expected, or temperatures are rising fast, consider picking the tomatoes and bringing them indoors to ripen. Here’s how to do it:
First, pick the tomatoes that are mature but not yet ripe. They should be full-sized, with a slight blush of color. Immature green tomatoes probably won’t ripen off the vine.
Wipe off any dirt from the tomatoes. If they’re wet, dry them to prevent mold growth.
Next, once you’ve picked the tomatoes, use one of the following two options.
Put tomatoes stem-side down in a basket on the counter. They will ripen, and you’ll be able to see how quickly they are ripening and use them as they become ripe. I put the most green tomatoes on the bottom and the ones closer to being ripe on the top layer.
Place tomatoes in a paper bag or box and close it. The bag traps ethylene gas the tomatoes produce and speeds up the ripening process. If desired, place a ripe banana or apple in the bag with the tomatoes. These fruits emit additional ethylene gas and will accelerate the ripening process.
Check the tomatoes daily. Depending on their maturity and the room temperature, the ripening process may take anywhere from a few days to a couple of weeks.
Remove any ripe tomatoes. A ripe tomato will be bright red (or yellow, orange, etc., depending on the variety), slightly soft to the touch, and have a fresh tomato scent.
What about the flavor? Will they taste as good as vine-ripened tomatoes?
Many gardeners believe tomatoes taste better when left to ripen on the vine. However, studies have shown that tomatoes picked at the mature-green stage and ripened indoors under controlled conditions can taste just as good as those left on the vine. There is one way to find out: try it for yourself and see if you can taste a difference.
Have fresh tomatoes? Try this delicious tomato and basil pasta recipe.
Storing Ripe Tomatoes
Once your tomatoes are ripe, store them at room temperature, away from direct sunlight, for use within a week. To extend their shelf life, consider canning, drying, or freezing your tomatoes.