How Much Cold Can Tomatoes Handle? How to Protect Your Plants from Cool Weather

How much cold can tomatoes tolerate? Tomatoes are notoriously cold-sensitive, so it helps to know what to do with the plants when temperatures drop. Your tomato plants may still have unripened or partially ripened fruit on them when the thermometer plummets to the freezing mark. Learn how to protect your tomato plants when the cold weather moves in.

Watch for Signs of Cold Tomatoes

Signs of cold damage on tomatoes, especially young plants, are not always visible. Here are signs to look for if you think your tomatoes are too cold:

• Light tan or gray spots appear on the leaves of young plants in the spring. A healthy plant can outgrow any damage from a brief cold snap.
• Any darkening of the leaf or stem tissue will later wilt and turn brown.
• The leaves are curling.

Signs of cold damage that show up on the plants later include:

• A damaged plant will have poorly set fruit.
• Plant growth will look stunted.
• Large-fruited tomato varieties will have deep crevices or holes and scarring in the blossom end (catfacing).
• A spring cold snap can result in distorted, malformed tomatoes when they are just ripening.
• Dry, brown scars that look like zippers running from the stem to the blossom end of the tomatoes indicate damage.
• Damaged tomatoes ripen unevenly.

Start Tomato Seeds at the Right Time

Prevent cold damage by starting your tomato plants from seed indoors at the right time. If you start the seeds too early it will still be too cold to move them outdoors. It's best to start tomatoes from seeds six to eight weeks before your area’s last projected frost date.

Don’t Expose Young Plants to Cold

Temperatures below 60 degrees Fahrenheit can subject highly cold-sensitive tomato seedlings to chilling injury. The damage won't be noticeable right away but the plants will experience stunted growth, poor flowering and fruit set, and catfacing.

Wait to plant the tomatoes until nighttime temperatures remain consistently above 60 degrees Fahrenheit. Take your time hardening off the plants before planting them outdoors in your garden or containers. 

Select Early- or Mid-Season Tomatoes

Choose cold-tolerant tomato varieties bred to set fruit in cooler temperatures below 55 degrees Fahrenheit. These varieties typically also mature earlier.

Early-season varieties mature in 52 to 70 days and mid-season tomatoes in around 70 to 80 days. There are many different varieties, both hybrid tomatoes and heirloom tomatoes. Popular varieties include Early Girl (52 days) and Better Boy (75 days). 

Ripen Green Tomatoes Indoors

If the weather forecast calls for frost, don't cover the plant. Instead, pick all unripe tomatoes from your plants and ripen them indoors.

How to Protect Tomatoes on Cold Nights

If there are still green or semi-ripe tomatoes on your plants around the time of your first average fall frost, keep an eye on the weather and consider these two ways to cover and protect your plants.

Bubble Wrap

If your plants are growing in tomato cages, protect them by wrapping bubble wrap around the entire cage, including the top, and use duct tape to secure it. It's a good time to prune the plant and remove excess foliage before wrapping it up. Remove the bubble wrap the next morning or you run the risk of excessive heat build-up under the plastic that will cook the plant.

Sheets and Blankets

You can also cover the plants with old sheets or light blankets held in place with sturdy stakes. Loosely tie a strong string around the plant to secure the cover from blowing away. Promptly remove the cover in the morning.