Washington State University Extension

Garden Tips

Ripening Green Tomatoes

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written October 2, 2015

Frost is coming and it is likely to be soon. The average date of the first killing fall frost in our area is October 15, but earlier for cooler spots. Before that happens and perhaps even a little earlier, gardeners should start picking mature green tomatoes. As we discussed last week, some types of mature fruit will ripen after picking. Tomatoes are one of them.

Our tendency as gardeners is to leave tomatoes on the vine in the fall until frost threatens and then quickly pick everything we can find that has some color. Some gardeners cover their vines with clear plastic to make a sort of greenhouse to keep the plants and fruit warmer during the day and protect them from frost at night.

However, covering plants with plastic or blankets is not going to help much because the fruit is injured by cool night temperatures below 50 degrees. Exposure to repeated chilly nights will damage the fruit, resulting in more fruit loss from decay. Once night temperatures start dropping below 40 degrees the damage is even greater.

The good news is that mature green tomatoes will ripen very well off the vine and still provide you with the wonderful flavor of homegrown vine-ripened tomatoes. There is no need to pick smaller green tomatoes that have no chance of ripening. Only pick mature green tomatoes. Telling the difference is a little tricky, but not hard. Generally, the fruit should be at least three-quarters the mature size expected for the variety. They will have turned from a bright green to a lighter green or whitish color. They do not need to have started turning red or the expected mature color yet.

Once the fruit are harvested, take them indoors and prepare them for ripening. This is done by first washing them with cool clean water and then allowing them to air dry completely. If any are cracked or split, they are more likely to rot before ripening so throw them out or use them in a recipe that calls for green tomatoes.

After roguing out the damaged tomatoes, you may want to sort those you have left. The ones that have developed a tinge of color will ripen first. Put these in one group, and then sort by “greenness.” The next step for many gardeners varies depending on just how many tomatoes they have and their capacity for storage. I recommend placing them in single layers in covered cardboard boxes. (Leave a little space between tomatoes.) Some folks wrap each fruit with newspaper and then place them in a box, but this is tedious and makes it difficult to check for both ripe or rotten fruit.

Tomatoes are the type of fruit that will ripen after picking and produce ethylene gas as they ripen. Exposure to ethylene gas from another source will speed up the process. If you are in a hurry for ripe tomatoes, place some of your green ones in a closed bag with some ripe bananas or tomatoes because they produce ethylene gas.

Our mothers and grandmothers placed their green tomatoes on the windowsill thinking that exposure to light was needed for ripening. Actually, they need the warmth not the light from the windowsill. Tomatoes will take about two weeks to ripen when kept at a temperature around 65 to 70 degrees. Cooler temperatures, but above 50 degrees, will result in slower ripening.

A chills is in the air so start harvesting your green tomatoes for ripening. Now is the time for action!

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