The arrival of fall often presents gardeners with a challenge: a large harvest of green tomatoes still clinging to the vine, threatened by the first hard frost. These fruits require specific conditions to change color from green to red. Fortunately, the ripening process is a natural biological function that can be successfully managed and accelerated off the plant. This article outlines proven methods to maximize your yield and achieve that final flush of red tomatoes.
Understanding the Ripening Process
The transformation of a green tomato into a red one is driven by the plant hormone ethylene, which initiates maturation. Tomatoes are classified as climacteric fruits, meaning they continue to ripen after being harvested because they produce a surge of this gas. This ethylene burst triggers changes, including the breakdown of chlorophyll, which causes the green color to disappear.
The red color develops due to the synthesis of carotenoids, primarily lycopene, the pigment responsible for the fruit’s final hue. This chemical conversion is sensitive to temperature, operating optimally within a narrow range. Temperatures between 68°F and 77°F (20°C and 25°C) are ideal for both ethylene production and lycopene synthesis. Ripening stops above 86°F (30°C) or below 50°F (10°C), meaning extreme heat or cold will halt color development.
Ripening Tomatoes Harvested Early
To ripen green tomatoes indoors, concentrate the naturally emitted ethylene gas in a moderate, stable temperature environment. The most effective method involves using a confined space, such as a paper bag, a loosely closed plastic container, or a cardboard box. Enclosing the fruit traps the ethylene, creating an autocatalytic effect that accelerates ripening.
To speed this process, introduce a “helper fruit,” such as a ripe banana or apple, which are prolific producers of ethylene. Placing one of these fruits alongside green tomatoes in an enclosed space can significantly reduce the time needed for color change. The ideal storage temperature is consistently between 65°F and 70°F, away from direct sunlight.
Check the containers every few days, removing any tomatoes that have ripened fully or show signs of decay, such as mold or soft spots. This inspection prevents the spread of rot. For longer-term ripening, wrap individual mature green tomatoes in newspaper before placing them in a box; this helps insulate them and absorb excess moisture.
Maximizing Ripening on the Vine
As the growing season nears its end, several actions can encourage remaining fruit to ripen before the first frost. One effective strategy is “topping” the plant, which involves pruning the main stem above the highest existing flower or fruit cluster. This redirects the plant’s energy away from producing new growth and toward maturing the existing fruit.
Reducing foliage can also be beneficial, provided the fruit is not exposed to scorching sun. Selective pruning of excess leaves allows more sunlight and warmth to reach the fruit, aiding ripening. Another technique is to slightly reduce watering, which induces a mild stress response. This stress prompts the plant to accelerate the maturation of its seeds and fruit, speeding up the ripening process.
Determining If a Green Tomato Will Turn Red
Not all green tomatoes will ripen after being picked; they must have reached the “mature green” stage. An immature green tomato, if harvested, will likely shrivel and rot without developing the necessary internal compounds. The distinction lies in the fruit’s physiological maturity, identified by a few physical indicators.
A mature green tomato will have reached its full size for its specific variety, often accompanied by a subtle change in exterior appearance. The skin transitions from a dull, dark green to a slightly lighter shade with a waxy or shiny sheen. This change in luster indicates that the internal development required for ripening is nearly complete.
If uncertain, a definitive test involves slicing one tomato in half. A truly mature green tomato will show a jelly-like substance around the seeds and fully formed seeds that are difficult to cut through. Conversely, an immature fruit has watery pulp and soft, underdeveloped seeds that are easily sliced, a sign that it will not ripen off the vine.