How To Ripen Green Tomatoes
By Carl Wilson, CSU Extension Horticulturist
The first week of September brought nights with temperatures in the forties to Denver. Seasons change quickly on the Front Range making this a good time to plan to get the most from summer tomato growing efforts.
Newly setting tomato blossoms, small and very green fruit won’t mature in the remaining growing season and are best pruned off. New, vigorous shoots also may be clipped back. Don’t remove an excessive amount of leaves as these supply nutrients to fruit. Light pruning directs plant energy to fruit that has a chance of maturing.
When fruit set is heavy, it can work against gardeners. Ripening numerous fruit takes a lot of energy from the leaves and tends to delay the whole crop turning red. If there are only a few weeks before frost and fruit is not ripening, try removing some of the mature green fruit to ripen what’s left on the vine.
Cooler September temperatures help fruit to ripen because the red tomato pigments, lycopene and carotene, are not produced above 85 degrees F.
As late September approaches, gardeners often try to extend the life of their plants by covering with cloth or plastic. Covering plants works well for nearly red tomatoes, but not as well for mature green ones. Research shows that chilling injury on green fruit occurs at temperatures of 50 degrees and decay losses are heavy on fruit exposed to 40 degrees F. Red ones well on their way to ripening better tolerate colder temperatures.
Before frost hits and plants go down, pick and bring fruit indoors to ripen. Extended exposure to cool temperatures interferes with ripening and flavor development. Clip fruit to leave a very short stem piece but not so long to punch holes in other tomatoes. Stems ripped out of fruit will open them to decay.
Eliminate green fruit, as research shows it’s more likely to spoil than ripen and never develops the flavor consumers want anyway. Mature green fruit will develop good flavor. Mature green tomatoes are well sized and have turned light green to white.
Sort and store fruit in groups that will ripen at similar speeds. Fruit may be “mature green”, "turning" with a tinge of pink to "pink" with 30 to 60 percent color showing, "light red" with 60 to 90 percent color present, and others "fully red" but not soft.
Store ripening tomatoes at 55 to 70 degrees F. Refrigerator temperatures of 40 degrees are too cold to ripen mature green tomatoes and are colder than desired for ripe ones. Ripening enzymes are destroyed by cold temperatures whether in the garden or in a refrigerator.
Ripen tomatoes in well-ventilated, open cardboard boxes at room temperature checking them every few days to eliminate those that may have spoiled. Mature green tomatoes will ripen in 14 days at 70 degrees F.
Cold weather and frosts can come in late September before typical October killing frosts arrive. Plan now to realize the biggest harvest from the vegetable garden.
Updated Saturday, September 25, 2010