Thursday, September 9, 2010

Plan now to ripen tomatoes

The first week of September brought four nights with temperatures in the forties to Denver. Tuesday morning following the Labor Day holiday I was surprised to find frost on the grass in the open space area near me in Southwest Denver (no frost in the residential area nearby though). 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 young, 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 your vegetable garden.

Photo credit: Roma tomato with mature green fruit, Staked tomatoes, Tomato harvest in box - all Carl Wilson


  1. Does the same apply to bell peppers? Should I be pruning off the blooms and smaller fruits on those plants as well?

  2. It is probably a good idea to do some judicious pruning of blossoms and small fruit (useable of course) to put energy into large peppers. This would be particularly true if you are trying to ripen remaining peppers to red or yellow at maturity.

  3. Re: peppers. Carl, do youknow of any growers/markets/farmers along Front Range harvesting/selling the 're-tooled' New Mexico Big Jim pepper you spoke of in about February? I did not plant. Willing to drive.

  4. Ever since the nights have gotten so cool, my tomatoes taste terrible! Is that normal? I was excited to try to ripen some of them as you suggest, but I don't want to eat the ripe ones I have right now.

  5. Cold refrigerator-type temperatures for extended periods do destroy tomato flavor. Perhaps cold nites have something to do with the flavor of your tomatoes. Anyone else have a similar concern? I have noticed that my tomatoes that were pink when ripe under hot August temperatures are now red (same variety). Temps below 85 F help the red pigments develop.