If you’ve ever tried growing tomatoes, you’ll know that they don’t like cold weather. Most gardeners are usually done with tomato harvesting by September.

But what if your plant is still producing fruit? After all, many regions experience warm spells well into the fall, which can trick some tomato plants into producing even though their fruiting season is technically over.

James Mastaler, PhD, Founder and CEO of Pistils & Pollen, an online plant care platform and community, says that as someone who gardens in containers on a rooftop in Chicago, “I’m always keenly aware of the race against the first frost. While I try to plan my tomato growing season accordingly, there are always a few fruits left hanging just shy of ripe when the weather starts to turn.”

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What do you do with a tomato plant that hasn’t died yet and is still full of fruit, albeit unripe ones? If you’re not ready to pull your tomato plants out of your garden, here’s when taking frost protection measures may still be worth it, even deep into autumn.

Why Frost Harms Tomato Plants and Fruit Flavor

Tomatoes are quintessential warm-weather crops, meaning they possess zero tolerance for freezing temperatures. As Christy Wilhelmi, Founder of online gardening resource Gardenerd, puts it, any fruit full of water (which tomatoes are) will be ruined by frost because water expands when frozen. “It will rupture the cell walls and make the fruit unpalatable,” she says.

In a nutshell, even if the fruit doesn’t freeze solid, prolonged exposure to cold fall air can prevent proper ripening and ruin eating quality. That’s why many tomato growers pick unripe fruit right before a forecasted frost and finish ripening the fruit at home, either on the counter or in paper bags in their pantries.

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There is, however, one instance where picking green tomatoes won’t work: if your tomatoes haven’t reached their full size.

Why You Shouldn’t Pick Undersized Tomatoes

If a hard, deep freeze is forecasted—and your plants are still full of unripe fruit—it is time to bring the harvest indoors. However, Wilhelmi stresses that if the tomato hasn’t reached full size on the vine, it will not ripen once brought indoors. “It will stay hard as a rock and then will start to shrivel without changing color,” she says.

As a gardener, you have only two options in this case: give up on your tomato plant and pull it out, or protect it from the first frosts to allow the fruit to reach its full size before picking.

How to Extend Your Tomato Growing Season in Fall

Although ripening tomatoes indoors is the easiest option, if the majority of the tomatoes on your vine haven’t reached full size, you can give them a little more time by protecting the plant from the coming frosts. If you live in a cold-weather climate, Wilhelmi advises using insulated fabric or floating row covers along with a thick layer of mulch to protect the tomatoes on the vine.

“This extends the growing season just enough to allow tomatoes to grow to full size,” she says.

You can also try building a simple cold frame to raise the temperature around your tomatoes just enough to keep them growing. Harvest your tomatoes as soon as they’ve reached their full size: don’t try to ripen them on the vine if the weather’s cold.

How to Ripen Green Tomatoes Indoors

Once you have harvested your mature green tomatoes ahead of a frost, you can easily coax them to ripen inside your house using a few traditional, reliable techniques.

• The paper bag method: Place a few mature green tomatoes inside a brown paper bag, along with a ripe banana or apple if you want to speed up the process. Ripe fruit releases ethylene gas, a natural plant hormone that triggers ripening. Fold the top of the bag loosely to trap the gas while allowing air circulation.
• The cardboard box or layer method: Alternatively, line a shallow cardboard box with newspaper or paper towels. Arrange your green tomatoes in a single layer so they are not touching each other, which helps prevent bruising and mold spread. Cover them loosely with another layer of paper and check them every few days to remove any fruit that has ripened or shows signs of spoilage.

By knowing when to shield your vines from a fleeting chill and when to harvest your green tomatoes for indoor ripening, you can enjoy homegrown flavor long after the outdoor tomato growing season has ended.

Sources:

• James Mastaler, PhD, Founder and CEO of Pistils & Pollen
• Christy Wilhelmi, Founder of online gardening resource Gardenerd

This article has been adapted from How to Ripen Green Tomatoes Before a Frost by Shelby Deering

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