Garden Tips: Tomatoes, pumpkins can ripen off the vine

Now that fall has officially arrived and the weather is turning cooler, gardeners are hoping to wring the last ripe vegetables and fruits from their gardens. They are asking, "Will they ripen after picking?"

Tomatoes

With tomatoes, the answer is yes. Tomatoes will ripen if they are mature and temperatures are above 55 degrees. Now is the time to harvest mature green tomatoes and ripen them indoors. Left outdoors and exposed to temperatures of 50 degrees or lower will lead to chilling injury. Tomatoes with chilling injury will not ripen, even if protected from frost. This is because enzymes needed for ripening break down under cooler temperatures.

Mature green tomatoes should be picked and ripened indoors at temperatures of 50 to 70 degrees. If kept at 70 degrees, they should ripen in about two weeks. The cooler the ripening temperature, the slower they ripen. How can you tell if a green tomato is mature? Mature tomatoes turn from a shiny dark green to a whitish green and may have a blush of red, orange or yellow.

Gently wash and air dry the green tomatoes, discarding any that have split or cracked skin. Place the fruit in a single layer in open cardboard boxes, not letting them touch each other. Cover the tomatoes with a layer of newspaper. (Tomatoes do not need light to ripen.) Periodically inspect the fruit and remove any that are ripe or rotten.

Grapes

What about grapes, do they ripen after picking? No, not a bit. Grapes must be left on the vine to ripen. However, this will be a problem once cool weather arrives because grapes will not ripen, even on the vine, after temperatures go below 50 degrees. If your grapes are not ripe when cooler weather prevails, you are out of luck.

If your grapes are not ripe, the reason might be that you planted a long-season cultivar that does not receive enough heat or growing days to ripen in our region. However, if your cultivar is one that should ripen here, there are several things that could be contributing to late ripening.

One possible cause is pruning. You may be "overcropping" your vines. Researchers have found that Thompson Seedless grapes need about 18 leaves per cluster for good fruit production and maturity. Not pruning properly and leaving too many clusters on the vine can result in small fruit that is slow to ripen.

Another cause of delayed ripening is significant leaf injury due to disease, such as powdery mildew, or insects, such as the grape leafhopper. Damage from pests decreases the foliage's ability to produce enough carbohydrates for vine growth and fruit production along with ripening. Yet another cause is poor vine growth due to soil conditions, excessive weeds, or shade. Finally, as with most of our growing endeavors, weather can be a factor in delayed ripening of grapes.

Pumpkins

With Halloween fast approaching, pumpkin gardeners might be wondering if their green pumpkins will turn orange, especially if the vines have died down. If pumpkins are mature and have started to turn orange when they are picked, the fruit may ripen more and turn completely orange if placed in a warm place to cure.

Pumpkins should definitely be harvested before a hard frost, whether the fruit is uniformly or only partially orange. After cutting them from the vine, place the pumpkins in a warm, dry place (80 to 85 degrees) for a week to cure, or toughen, their skin. During the curing process, fully mature fruit may turn orange.

-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

This story was originally published October 16, 2014 at 12:00 AM with the headline "Garden Tips: Tomatoes, pumpkins can ripen off the vine."