If you grow tomatoes in Missoula, you already know how this ends. Sometime in September or early October, a cold night takes the vines and every green tomato still hanging on them. Missoula’s median first fall frost is late September (about September 26 at the airport, per NOAA’s 1991 to 2020 normals), and in about 1 year in 10 it arrives by mid September. The question is what to do with all that unripe fruit before that happens, because green tomatoes are not a loss. Handled right, the mature ones will ripen indoors and feed you into October and beyond.
Pick Before the Frost, Not After
This is the part people get wrong. A tomato that has frozen, the kind that turns soft and water-soaked within a day or two, will not ripen properly and will mostly just rot, so compost it rather than boxing it up with the sound fruit. A light frost may only nip the leaves, but there is no telling in advance how hard a night will hit. So the whole game is picking ahead of the cold night, not cleaning up after it.
Start watching the forecast around the second week of September. The first frost here usually comes on a clear, calm night after a cold front moves through. When you see a night predicted at 35 degrees or lower, treat that as your deadline. Frost pockets in Missoula’s valley bottoms can freeze when the official forecast says 36.
If the forecast shows one cold night followed by another week of warm weather, you can cover the plants instead and keep them going. Frost protection has its own post. But when the cold looks like it is settling in for good, strip the vines.
Which Green Tomatoes Will Actually Ripen
Not every green tomato is worth bringing inside. The ones that ripen are the ones that have reached what growers call the mature green stage. Cut one open and the seeds are surrounded by gel, not solid flesh. From the outside, look for fruit that has sized up fully and shifted from grass green to a paler, almost whitish green, often with a faint blush starting at the blossom end.
Those will ripen indoors reliably. Small, hard, dark green fruit picked mid-growth mostly will not. It is not worth the counter space, and that is exactly the fruit to cook instead. Fried green tomatoes are the famous answer, but green tomato salsa and chutney are better ones, and they can handle the truly immature fruit.
How to Ripen Green Tomatoes Indoors
Forget the sunny windowsill. Ripening after picking has almost nothing to do with light and everything to do with temperature and ethylene, the ripening gas tomatoes produce on their own.
Here is what works. Pick the fruit dry, leave the little green cap on, and skip washing them until you are ready to use them. Damp fruit rots. Lay them out in a single layer somewhere around 65 degrees, which is where MSU Extension says picked tomatoes ripen best. Anywhere from about 60 to 70 works. A spare room or a basement usually fits, and a garage works only while it stays well above 50. A cardboard box with a sheet of newspaper between layers is the classic setup because it holds a little ethylene near the fruit and makes it easy to check on them.
If you want to speed a batch up, put a ripe banana in the box. Bananas throw off ethylene and will pull the tomatoes along faster. If you want to slow things down and stretch your supply, keep them cooler and skip the banana. At 55 degrees, mature green tomatoes can take three or four weeks to color up, though quality can slip a little at that temperature. Below about 50, they may never ripen properly or develop good flavor. Staggered that way, a few fresh tomatoes at Thanksgiving is not out of the question in Montana.
Check the box twice a week and pull anything that is coloring, plus anything showing soft spots. One rotting tomato will take its neighbors with it. Ripe tomatoes keep their best flavor on the counter. A few days in the refrigerator is fine if you need to hold them, but flavor starts to fade after about a week of cold, and cut tomatoes belong in the fridge.
The Whole-Plant Trick
Some gardeners pull the entire plant, roots and all, shake off the soil, and hang it upside down in a garage or basement. The fruit keeps ripening on the hanging vine. If you have the space and only a few plants, it is worth trying. If you have a dozen sprawling plants, the box method is far less of a production.
Either way, do not leave the stripped or pulled plants lying in the garden if they showed disease this year. Healthy vines can be cut at the soil line and left as mulch, with the roots staying in the ground to feed soil life over winter. Diseased vines should leave the property or go to a hot compost, because blights overwinter on dead tomato tissue.
One more storage option deserves a mention: the garage shelf. An attached garage that stays frost free can work for ripening in early fall, but Missoula nights cool off fast in October, and an unheated garage can slide below 55 degrees, where ripening slows way down. Leave a thermometer out there for a few days before trusting it, sort the box weekly, and move the fruit to a basement or spare room once the garage gets cold. The basement stairwell often holds a better range than the garage itself.
And if you end up with more mature green fruit than you can ripen or cook, remember that green tomatoes trade well. Missoula’s food-preserving crowd knows exactly what to do with a box of them, and late September is a good time to offer a box around your community garden or the neighborhood.
Taste Honestly, and Take Notes
Indoor-ripened tomatoes are good. They are not August tomatoes, and pretending otherwise sets you up for disappointment. Fruit picked with a blush already showing comes closest, since MSU Extension says tomatoes picked at that breaker stage ripen off the vine with full flavor. Use the box tomatoes for cooking, sauces, and sandwiches, and save your expectations of perfection for next summer.
While you are out there picking, take five minutes and write down which varieties actually ripened for you this year and which ones were still stubbornly green in late September. In Missoula’s short season that note is worth more than any catalog description, because a tomato that cannot beat a typical late-September frost is the wrong tomato for this valley no matter how good it tastes somewhere warmer.
If this season felt like a scramble, the Missoula Planting Calendar lays out frost ranges and planting windows, and the roundup of short-season tomato varieties for Montana is a good place to start next year’s list.
Sources
- Montana State University Extension, Growing Tomatoes in Montana
- Cornell Cooperative Extension of St. Lawrence County, Ripening Green Tomatoes Indoors
- Colorado State University Extension, PlantTalk Colorado: Ripening Tomatoes Indoors
- Zhang et al. (2016), Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation, PNAS
- NOAA NCEI, U.S. Climate Normals 1991 to 2020 (Missoula International Airport)