Few things in life are as frustrating as waiting for that first green tomato of the season to ripen or your green tomatoes turn red before frost kills your plants. Ripening is a complicated process in tomatoes, making it difficult to predict exactly how long it will take a fully-formed green tomato to turn red.
Inside the Machine
Tomato ripening is a complicated process involving hundreds of chemical reactions. Pigments like carotene and lycopene are produced as chlorophyll breaks down, causing the gradual coloration of the fruit. At the same time, acid levels are rising, causing starches in the fruit to convert to sugars and softening the tomato. Under ideal conditions, this can all happen in as little as a week, but often requires 20 days or longer in some weather conditions.
Factors Affecting Ripening
Several factors play key roles in ripening tomatoes, such as ambient temperature, soil temperature, the plant's natural ability to produce the hormone ethylene and even the number of fruits requiring ripening. Ambient temperatures above 85 degrees Fahrenheit or soil temperatures above 80 degrees are the primary reasons tomato plants put the brakes on ripening. Occasionally, a plant is so heavily laden with green fruits that it simply lacks the energy to support them all to ripening. Some gardeners remove the smallest tomatoes on an over-burdened plant; increasing mulch and water for plants suffering from hot roots can also speed ripening.
Tomato fruits are sometimes ripened indoors by gardeners when sunscald or insect pests are a chronic problem or when frost begins to threaten. A tomato picked at the "breaker" stage, when a blush of its final color appears, will ripen fully on the kitchen counter if kept out of direct sunlight. Tomatoes harvested at the breaker stage contain all the sugars of a fully vine-ripened tomato and will develop the same flavor.
Hastening the Final Harvest
As winter looms and frost threatens, many gardeners rush to the garden to cover their plants nightly, hoping those remaining fruits will ripen before the plants die. You can speed ripening in your tomatoes by removing any green fruits that are not fully developed -- these tomatoes are unlikely to develop further due to cooling temperatures anyway. Withholding water and fertilizer also helps to speed the ripening process. When a killing freeze is predicted, uprooting your tomatoes and hanging them upside down in a garage or basement will allow the remaining fruits to ripen on the vine.
- University of Georgia Extension: My Tomatoes Won't Turn Red
- University of California Cooperative Extension: Ripening Tomato Fruits
- Purdue University Extension: Tomatoes Not Ripening?
- Rutgers New Jersey Agriculture Experiment Station: Why Tomatoes Take Their Sweet Time to Ripen
- Cornell Cooperative Extension: Why Aren't My Tomatoes Ripening?
- Purdue University Cooperative Extension: Tomatoes
- Hemera Technologies/Photos.com/Getty Images