I prefer growing tomato plants after the last frost date and the start of spring. But sometimes they get hit by an unexpected frost. That’s why it’s important to know how much cold the tomato plants can survive and how to protect them.
How cold is too cold for tomato plants? Any temperature below 50° F is too cold for tomato plants. The tomato seedlings won’t germinate, the young tomato plants will have stunted growth, and the mature tomato plants won’t produce fruit. A temperature below 32° F will cause frost that will kill the tomato plants and fruits.
A tomato plant grows well with the right amount of sunlight and heat. You need to know the right time to grow them. And you need to know what to do when an unexpected drop in temperature happens during the growing season.
What temperature will kill my tomato plants?
Any temperature below 32° F causes frost and will kill the tomato plant and fruits. The tomato plant will be able to survive even up to a temperature drop of 33. The tomato plant temperature tolerance varies between 50 and 85 degrees Fahrenheit.
But surviving does not mean the tomato plant will thrive. The growth of the plant will be stunted and it will take a long time to produce fruit if any at all.
If there are any tomatoes growing on the plant, they may freeze because it is too cold for tomatoes. This causes permanent damage to them and you will need to dispose of them.
You can harvest the green tomatoes just before the cold or frost hits the plants. The green tomatoes can be put into storage in a cold, dark place. Once you want to ripen the tomatoes just move them to a dry place.
The best temperature to grow tomato plants is in the range of 70 to 85° F. This is also the optimal temperature to germinate the tomato seeds. It will take a lot longer for the seeds to germinate at a temperature below 70° F.
Can tomatoes recover from cold damage?
Tomatoes need warm weather to grow well so any extended period of cold will kill the tomato plants.
If the drop in temperature is just for a few hours, there is a good chance that the tomato plant can recover. This depends on the maturity of the plant as well.
Seeds won’t germinate when the temperature drops below 70° F. But the tomato plant may recover.
How well the tomato plant recovers also depends on how low the temperature has dropped and how much is the damage.
If the plant and tomatoes have been hit by frost, this can lead to freezing of the tissue. The cells freeze and rupture causing irrecoverable damage to the plant.
This may be visible when the plants and fruit have wilted and turned black or lost shape.
The best thing you can do is allow the plant to thaw itself out and not touch the plant. Check the plant after a few hours to see the extent of the damage.
If the seedlings and leaves have turned black, there is no way to recover them. You need to dispose of them and start a new batch.
If the plant is mature then check the leaves and stem. If just the edges of the leaves have turned black, the plant will recover.
If the entire leaves have frozen and turned black, you need to prune them off. You need to do the same for the tomatoes that have been damaged by the frost.
If the lower portion of the main stem has turned black, the plant is going to die and there’s nothing you can do about it. You need to dispose of the plant and start growing another one.
How do I protect my tomato plants from cold nights?
You need to keep an eye on the temperature of your area when growing tomato plants in the spring and summer. If the temperature is going to drop below 50° F, you can take steps to keep the tomato plants warm.
Grow the tomato plants in the right season
Make sure you start growing the tomato plants when the night temperatures are above 60° F. Check the frost dates of your area and only start growing the tomato plants after the last frost date when spring begins.
This will help increase the chances that the night temperatures do not drop to below freezing.
If you have a short growing season, you need to germinate and grow the tomato seedlings indoors. Once the frost goes away and temperatures rise, you can transplant the seedlings outdoors in your garden or containers.
Another option is to grow tomato varieties that can tolerate a bit of the cold weather. This includes Russian varieties like Anna Russian and Azoychka. These varieties are capable of even withstanding a little frost.
Use a cover to protect the tomato plants
The simplest thing you can do is just cover the tomato plants in the night when you know a temperature drop is coming.
Before you can use a cover, make sure to water the tomato plants well. A well-hydrated tomato plant can survive the cold much better than a dry one.
This could be a simple plastic cover like a garbage bag that you place on top of your tomato plants. Make sure to use a stake and keep the plastic from touching the tomato plant.
If the plastic touches the plant, it will still cause the tomato plants to get affected by the cold.
Some other options you can use to cover the tomato plants are lightweight blankets, old sheets, and tarps.
You can also use an old plastic bucket as long as it’s enough to cover the plant. Make sure the bucket does not have any holes in it.
If you’re growing seedlings outdoors, you can use a tray cover to protect them. Or it’s even better to move them indoors.
If you have some LED lights or Christmas lights, you can place them on top of the plant inside the cover. This will give them an additional source of warmth during the night.
The cover will help keep the temperatures at least 2-4 degrees higher than the outside temperature. Make sure to remove the covers in the morning to allow the plant to breathe and soak in the light and warmth of the sun.
Bring the tomato plants indoors
If you’re growing the tomato plants in a container, you have the option to bring them indoors during cold nights. Be careful when moving the tomato plants that you don’t damage the stems and leaves.
I would recommend growing determinate varieties of the tomatoes when growing them in a pot. They are limited to a certain height so you can grow them in a 10-20 gallon pot. This makes it easier to move indoors without straining yourself or the plant.
If you are growing the tomatoes in a heavy pot or a grow bag, don’t try to lift the pot. You can injure yourself, break the pot, or tear the grow bag from the bottom.
A better option is to use a moving tray and place the pot or grow bag on this tray. This will make it easier to transport the tomato plant indoors.
Make sure to move the tomato plants indoors to an area where there is plenty of warmth for the night. You don’t want to move them to the garage or basement where there’s not much difference than the outside temperature.
The next morning as the sun comes out, you can bring the potted tomato plants outside so they can get the air, sunlight, and heat they need to continue growing.
Fact Checked, Written, and Published by Kevin Rodrigues
Kevin is the founder of Gardening Mentor, a website that aims to teach people to grow their own food in a limited space. As a self-taught gardener, Kevin has spent several years growing plants and creating gardening content on the website. He is certified in Home Horticulture and Organic Gardening from Oregon State University. He has a Post Graduate Diploma in Horticulture and Landscape Gardening from Mumbai University.
Read more