The Mysteries of Ripening Tomatoes

These tomatoes are beginning to ripen, but only a few are bright red and glossy.

Around this time of year, a funny thing happens to many folks’ tomato plants: the green fruit, plump and perfect up to this point, refuses to turn red. Weeks pass, and those green tomatoes just sit there, waiting for birds and bugs to peck holes in them. What has caused this, and what can you do about it?

It’s the Weather . . .

The major culprit in halting the ripening process is the temperature. When the weather stays above 80 to 85 degrees for more than a couple days, the plant stops producing lycopene and carotene, the two things responsible for turning the skin red. At the end of summer, when temperatures drop, the same thing happens: no more lycopene and carotene, so no more ripening.

Chocolate Cherry Tomato turns deep purple — nearly black — when fully ripe.

You can’t change the weather, and providing more shade really won’t help unless it comes with a substantial drop in temperature. (Whatever you do, don’t strip the leaves around the fruit to let more sun in. Not only will this not help the tomatoes turn red, it may toughen their skins, making them less tasty!) So if your tomatoes are staying green and the thermostat is still climbing, you have to harvest them and help them finish ripening another way.

Finish Ripening Indoors

The best way to do this in midsummer is to carefully pick the green fruit and then store it indoors for a couple weeks. The idea here is to capture the fruit’s ethylene, which makes them ripen (the lycopene and carotene just turn the fruit red, not actually ripen it). So here’s how to do this:

Of course, “ripening” doesn’t necessarily mean turning red! These Honeybee cherry tomatoes turn a rich gold when ripe.

If you only have a few tomatoes:

  • Place a few tomatoes in a paper bag, along with a banana or apple, close it, and set it on a shelf in the pantry. The banana or apple will release a lot of ethylene, triggering the tomatoes to ripen. Keep an eye on the fruit, checking it every few days.

or:

  • Wrap each tomato loosely in newspaper and then place them on a shelf, such as a pantry or (push comes to shove) closet. Again, monitor the progress of the ripening.

If you have lots of tomatoes:

  • Line the base and sides of a cardboard box with newspapers, then carefully place the tomatoes in the bottom, filling it no more than 2 layers high. Place another layer of newspaper on top of the upper layer, and close the box. Use multiple boxes if you have tomatoes left over.

    Tomatoes are ripe when their skins turn glossy and they feel heavier than they should.

  • Store the box in a warm, dry indoor place (pantry floor), checking the fruit after a week for signs of ripening.

You may wonder why you don’t just put the tomatoes with a banana in a big plastic bag, seal it up, and speed up the whole process. Well, the issue is that although you need to trap the ethylene, you risk rotting the fruit by restricting airflow. That’s why porous cardboard and newspaper are recommended; they will allow some air to circulate while also trapping enough ethylene around the fruit to help it ripen.

Green Shoulders

Irritating but not a showstopper, green shoulders can be cut away and the rest of the fruit enjoyed. Some varieties are simply prone to green shoulders, and should be given some shade as they ripen.

Warm midsummer weather can also cause tomatoes that have already begun to turn red to stop, leaving the top part of the fruit green. This is called “green shoulders,” though it can extend halfway down the fruit. What has happened here is that too much direct sunlight combined with high temperatures have caused the breakdown of chlorophyll within the fruit to stop. Chlorophyll, you may remember, is what turns plants green. Your tomatoes will stay green if this happens! But not to worry — green shoulders can be cut away and the rest of the tomato enjoyed. And next year, you can provide a little more shade cover for your tomato plants and probably avoid the issue altogether.

Ripening a Green Tomato Variety

You might wonder how to tell if your green tomatoes are actually ripening or have stalled out on the vine. Of course, the best way to tell may be to cut into one, but there are other clues:

Although this is a green tomato, note the gold tones on the skin. These begin whiter or paler, only darkening to yellow when fully ripe.

  • Green tomatoes usually have white streaks or patches that will turn yellow when fully ripe.

  • Ripe tomatoes acquire a bright, glossy shine on their skins.

  • Ripe tomatoes feel heavier than they should.

If you think your green tomatoes have stalled in the high midsummer heat, follow the same process as for red varieties, using the three criteria above to judge when they have ripened indoors.

About Sappho Charney

Sappho Charney is a garden writer living in Lubbock, Texas.

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