How Cold Is Too Cold for Tomato Plants?

How Cold Is Too Cold for Tomato Plants?

No garden is complete without at least one variety of tomato growing in it. Luckily tomatoes are the most abundant vegetable in the world, so there is a good chance that one and most likely several types of tomato plants will be growable in your garden. In order to enjoy the fruit of tomato plants, you will need to provide lots of sunlight and high daytime temperatures for the entire growing season. 

If you are in a climate where these things are scarce, do not fret; there are ways to still enjoy tasty homegrown tomatoes, but you will need to do the extra work. To create light where there is none is a bit of a tricky endeavor, but most climates will receive enough sun during the summer months to sustain tomatoes. Keeping tomatoes safe from cold weather is another challenge entirely and what this article focuses extensively on. 

What Are the Coldest Temperatures Tomatoes Can Survive?

Tomato plants love warm temperatures, and tomato seeds need high soil temperatures to germinate. Cold temperatures can be deadly to tomato seedlings, and a cold night or two can lead to stunted growth and low pollen production. It is important to keep tomato plants warm and harvest before frost dates to avoid undesirable tomato crop issues.

50 to 55 Degrees (F)

Mature tomato plants are able to withstand temperatures as low as 50 degrees with little trouble if it is a brief exposure. Cool nighttime temperatures of 55 degrees or lower can help ripen fruit and signal that the season is almost over. If daytime heat moves out of the ideal temperature range of 70 to 80 degrees, then stunted growth, wilted tomato leaves, and subpar fruit can be expected. 

40 to 49 Degrees (F)

As the season moves closer to frost dates, temperature dips can become dangerous. Chilling injury will occur if cold temperatures persist for more than a few nights in a row. The effects of this on a tomato garden can be seen in decreased resilience against pests and disease, weakened growth, and other cold damage effects. Even with plenty of sunlight, the process of photosynthesis can be slowed by repeated daytime cold temperatures and frequent cold snaps.

33 to 39 Degrees (F)

If you only have blooms and green tomatoes and your temperatures are in this range, you may have a hard time getting fresh tomatoes. At these temperatures, blossoms will drop, and fruit production will halt. Plants may survive but will produce very little and will appear sickly and weak. Common tomato deformities, such as catfacing and pitted fruit, are more likely in colder temperatures, so choose a fast-maturing tomato variety if you have short summers.

32 Degrees (F) and Below

At this point, you will need to add extra heat to your tomato plants if you want them to thrive at any life cycle stage. Tomato seeds will not germinate, tomato seedlings will die, and mature plants will experience severely stunted growth if exposed to freezing air temperatures or frigid soil temperatures. You must harvest tomatoes before exposure to these temperatures kills the entire cold tomato plant and ruins any existing yield you would have gotten.

How to Keep Tomatoes Warm in Cold Conditions?

39-in. Single Garden Bed Cold Frame Mini-Greenhouse Plant Protector - Lightweight and Portable

The popularity of a home tomato garden has given way to many products and methods that can help you increase soil temperatures, protect tomatoes from cool nighttime conditions, and add warmth when your plants need it most. Using the right techniques can increase your tomato harvest and help prevent cold damage and plant injury from ever happening.

TechniqueMaterialsProcess
Choose a Climate Appropriate VarietySeed catalog Check your USDA hardiness zone and choose the right variety for your local climate conditions
Start Seeds IndoorsTomato seeds, tomato dirt, amended soil, pot or seed trayPlant tomato seeds in a seed tray and place them where they get plenty of heat until they germinate, then provide sunlight
Finish Plants InsideTomato plants in a container, a room with heat and ample light sourcesMove plants inside when winter begins in cooler climates to allow the fruit to ripen fully
Cold FrameOld window or transparent boxPlace box over plants to shield them from wind damage but allow in sunlight and cause the interior temperature to increase gradually
ClochesDome shaped cold resistant material that fits over tomato seedlings and small transplantsPlace a cloche over plants before dark to protect them from the wind or cover them with a clear material to keep them warm during an extended period of cold
Row CoversBurlap or heavy fabric that keeps wind and moisture off of tomato plants, rope, and fastenersCover the rows at night when frost is expected to keep your plants alive later into the year.
Build a Green House Glass panels, frames, and fasteners Build a glass frame around your tomato plants to control temperatures all year round

Climate Appropriate Variety

Choosing cold-tolerant tomato varieties that are viable in your climate can help you grow tomatoes no matter where you live. Some tomato cultivars, like bush beefsteak, need full summer sun for several months and will take most of the late summer to plump up. Smaller cultivators like Tiny Tim can be done before the summer is over, even in northernmost climates. 

Start Seeds Indoors

To start tomatoes where spring frosts are frequent, you can skip the cold soil outdoors and start your seeds inside. A seedling heat mat and supplemental light can get your tomatoes growing large before spring even heats up. If there is any chance of a late frost or you have cold soils well into April, you can start seeds indoors to prolong your growing season. 

Finish Plants Inside

At the end of the season, early frosts can wipe out otherwise healthy tomato plants. Cold-tolerant tomato varieties can be moved outside during the day and brought in at night to avoid below-freezing temperatures. Make sure to plant tomato seedlings in fertile soil or potting soil with amendments and use plastic containers. Make sure the area you are moving the tomatoes into is pest free and has the airflow, light, and temperature requirements needed for a perfect harvest. 

Cold Frame

Sometimes we start our seeds outside, and then the cooler weather returns. Exposed seedlings could be subject to late frost damage and set your days of harvest back by weeks. A cold frame made of old windows or transparent totes can be placed over young plants to protect them from a few days of cold weather. For optimal plant growth, open or remove the frames in the morning to allow more sunlight and airflow near the seedlings and increase the soil temperatures.

Cloches

A quick way to protect seedling growth is to place cloches over plants at night to keep out cold night temps. If the cloche is transparent, it can be left on during the day but ensure there is enough airflow to avoid extreme heat in direct sunlight. Cloches can help you adjust to strange weather patterns and save plants already growing in your garden from sudden frost for a prolonged cold spell. 

Row Covers

Valibe Plant Covers Freeze Protection 10 ft x 30 ft Floating Row Cover Garden Fabric Plant Cover for Winter Frost Protection Sun Pest Protection (10FT X 30FT)

It is not practical to place cloches or build cold frames around tall and mature garden plants. Tomatoes approaching harvest in cooler regions can be aided with a cloth row cover. These cover options allow you to protect the tomatoes from frost while allowing mature plants the daytime heat and sunlight needed for the growth of plants. Cold exposure will damage your plants, and row covers can keep your garden investments safe right when you are about to harvest your delicious vegetables.

Build a Green House

In some climates, the only way to grow tomatoes from seed to harvest will be in a greenhouse. A well-constructed greenhouse allows you to moderate the light, airflow, and temperature conditions inside the structure. Pre-fabricated greenhouses can be expensive but are extremely helpful at prolonging the growing season. Makeshift greenhouses can also be thrown together for as little or as much money as you feel like spending. 

Will Tomatoes Heal from Frost Damage?

Tomatoes with Frost

Similar to frostbite in humans, freezing temperatures damage plant tissues and make recovery impossible. Since the frost damage is localized, there is still a chance the plant can continue to grow and produce fruit. If only the tips and ends of the plant are frost-damaged, recovery should be no problem assuming the temperatures warm up. If there will be frost again before harvest time, then you will need to protect the plants from the second blast of frost damage.

If the frost damage is severe and affects the stems or roots, then there is a good chance the plant will not survive. Since tomatoes are annuals, there is no point in trying to care for a plant that will not produce any fruit before it dies. It is important to keep the soil temperatures above freezing and never water with cold water. The leaves and fruits of the plants are much more resistant to cold than the core of the tomato plants, but all need to be protected from frost damage and prolonged cold fronts.