Master Gardener: Why Do I Have So Many Green Tomatoes?

If your garden is anything like mine, there are plenty of green tomatoes hanging on the vine – perhaps more than usual for this time of year. It’s time to get these “greenies” ripened before that first frost hits.

Why are we seeing so many green tomatoes on the vine this year? It has to do with weather – no surprise, right? That cold, wet spring and late summer set our gardens back by about two weeks and caused late pollination and fruit set for many vegetable plants – especially tomatoes.

When it comes to pollination, tomatoes are very temperamental. For successful pollination, they require temperatures to be between 70 and 85 degrees. We saw temperatures well below that threshold into July, causing blossom drop and late pollination.

It also takes six to eight weeks from the time of pollination until the tomato fruit reaches its full maturity – meaning that the tomato fruit is fully developed, but not ripe. This is known as the “mature green” stage.

Delayed pollination due to our late start to summer is one cause for those green tomatoes – but there’s another reason too. In addition to an optimal temperature range for pollination, tomatoes have an optimum temperature range for ripening.

Ripening and color development in tomatoes is controlled by two factors: temperature and the naturally occurring hormone, ethylene.

The optimal temperature for ripening mature green tomatoes is between 68 and 77 degrees. The further the temperature moves in either direction from that optimum, the slower the process will be.

In addition, when temperatures are consistently over 85 degrees the production of lycopene and carotene, which are the pigments that give tomatoes their color, stops. This causes the fruit to remain in a mature green stage until conditions become more favorable.

This means that extended periods of excessive heat can significantly slow down or even stop the ripening process in tomatoes. Combine that with our chilly start to summer, and the end results are green tomatoes.

With cooler temperatures on the horizon, the ripening process should kick into gear. But you can also ripen tomatoes off the vine. Here’s some tips:

• Choose tomatoes that show some coloring – from light green to creamy white to pale pink, along with any mature green fruit. These are usually the largest tomatoes on the vine.
• Disregard any fruit that is immature. It will not ripen off the vine and can be composted.
• Place tomatoes that are showing some coloring on a kitchen counter, out of direct sunlight. The naturally occurring ethylene gas in the fruit will gradually ripen it. This method works best on tomatoes that have some coloring as they produce more ethylene. Tomatoes will ripen anywhere within a few days to up to two weeks depending on the ambient temperature and how much coloring the fruit has.
• Mature green tomatoes with little coloring produce lower levels of ethylene and should be ripened in a breathable paper or cotton bag with an apple peel or banana. These fruits produce a great amount of ethylene gas and will speed up the natural ripening process. Check the tomatoes daily and remove any spoiled tomatoes or fruit (replace banana or apple peels if needed). Mature green tomatoes usually ripen within a week using this method.

Oh tomatoes, how we love growing you, but we have once again confirmed that you are truly the prima donna of the garden.

Candace Godwin is a Certified Idaho Master Gardener. The University of Idaho Extension, Kootenai County Idaho Master Gardener program is located in the UI Research Park, 958 S. Lochsa St., in Post Falls. Learn more about us at https://www.uidaho.edu/extension/county/kootenai/garden or on Facebook. Visit us in person, email us at kootenaimg@uidaho.edu, or call us at (208) 292-2525. IMG services are free to the public.