Whether you're starting seedlings, sowing directly into the ground, or just want to know how far you can push it regarding the slowly ripening tomato plants on your vines, this guide covers the safe temperature ranges of tomatoes so that you never ruin a precious crop. Let's find out exactly how cold is too cold for tomato plants.
What Is The Lowest Temperature That Tomato Plants Can Survive?
While tomato plants can survive in various conditions, the climate can reach points where it’s too cold for them to prosper or survive.
To be exact, tomato plants can survive in temperatures above freezing (32°F or 0°C). However, if temperatures dip below freezing, the frost or freeze may kill your tomato plants.
While your tomato fruit plants can survive in non-freezing conditions, temperatures below 55°F can still cause damage to your tomato plants.
The duration and the exact temperature of the frost or freeze can determine how badly your tomato plants are impacted, whether they suffer a mild amount of frost damage or die during the frost.
There are some predictable results you can expect in different ranges of temperatures.
Temperature Range Chart
|Even a brief exposure to air at this temperature can lead to plant death.
|33°F to 40°F
|Exposure over long periods increases the risk of chilling injury, which can include stunted growth, wilting leaves, and pit formation on fruits
|41°F to 50°F
|Brief exposure can cause mild damage or reduce pollen production. More prolonged exposure can cause chilling injury
|51°F to 55°F
|Prolonged exposure results in growth stunting, reduced yield, reduced texture and flavor of fruits, and flower loss
Temperatures that are too cold will kill tomatoes and most other warm-weather plants very quickly. As they die, the leaves and stems of the plant will turn darker before eventually wilting and turning brown.
At temperatures below 55°F, tomato plants will stunt and experience a reduced fruit yield. Also, the seeds inside the tomato fruits may sprout in a process known as vivipary.
At temperatures below 50°F, tomato plants at the flowering stage will begin to produce less pollen and experience a reduced yield of fruit. There may also be formations of pitting, catfacing, or other scarring deformities on the fruit that later forms.
At temperatures below 45°F, tomato plants will be at a higher risk of wilting and frost injuries, in addition to the reduced pollen and fruit yield that results from the colder temperatures.
This is especially true if the tomato plant is at its flowering stage during the chill. While it may not cause immediate or drastic injury, it will ultimately harm your harvest if your tomato plant is exposed to these temperatures.
At temperatures below 40°F, tomato plants will begin to wilt and brown from chilling injury. At best, the plant will experience stunting, wilting, and pitting of fruit. At worst, the tomato plant may even die from the cold or an unrelated disease due to its weak state.
The plant will become less hardy and more susceptible to disease. It becomes especially critical to protect your tomato plants as the temperatures get colder.
As the temperatures decline, the flavor and texture of tomato fruits will gradually worsen, and the cold soil will prevent the tomato plant from absorbing the nutrients it needs to grow and yield fruit properly.
When Should I Plant My Tomatoes?
If you’re growing tomato plants in a cold climate, proper timing is critical to ensuring a good harvest.
Referring to your USDA hardiness zone and the time needed to grow your chosen tomato variety is a great start for planning. You should also refer to your region's frost dates.
Assuming you’d like to grow a variety, such as Polar Baby tomatoes that mature in 60 days, you should plan to have all of your tomatoes harvested before the first frost date in your area.
Harvesting can be a long process, and in this case, we can assume four weeks of harvest from the Polar Baby tomatoes — meaning that you should plant approximately 90 days before the first frost.
If the first frost is on a day like August 10, it’s critical to plant before May 9 to ensure you have enough time for your tomatoes to reach maturity and for all of your tomatoes to be harvested.
You can plant much earlier in many climates. And planting earlier is critical for many gardeners since it gives you the time to address unexpected problems and ensure even your struggling tomato plants have a successful harvest.
Choosing Varieties That Can Survive Colder Temperatures
While using methods like row covers to combat the cold weather can be an excellent way to reduce the damage, it can only do so much.
And if you live in a region with frequent long periods of freezing temperatures, you can save yourself a lot of grief by choosing a variety of tomatoes meant to survive and thrive in your climate.
To start, you should determine what USDA zone the area you live in is classed as using their hardiness zone maps. If you live in a lower number zone, such as 1 to 4, it will be difficult to grow tomatoes that require a long growing season or consistently warm temperatures.
Therefore, it’s important to research the cold tolerant varieties and choose one that works for your garden.
Cold tolerant tomatoes generally offer a lower yield and smaller fruit but can thrive in cold temperatures that other tomato plants can’t.
And despite some of the drawbacks associated with these varieties, they still offer incredibly fresh and delicious fruit in the comfort of your backyard — whether in a warm or freezing climate.
Some of the most common cold tolerant tomatoes to consider are Cold Set tomatoes, Glacier tomatoes, Northern Delight tomatoes, Polar Star tomatoes, and Polar Baby tomatoes.
These varieties tend to ripen in 1 to 2 months, with weights ranging from 1 to 4 ounces depending on the variety.
You can also consider fast maturing tomato plants that will outpace even the harshest winter, including Sub-Arctic Plenty tomatoes, Tiny Tim tomatoes, Siberian tomatoes, and Fourth of July tomatoes.
These tomatoes can mature in as little as a month and a half and can yield tiny tomatoes or fruit as large as 4 ounces.
Sprouting Seeds Indoors
As noted before, planting your seeds earlier can be a good thing. It gives you much more time to grow your plants and have a successful harvest before the first frost arrives in your area.
Planting early will give you the extra time you need to succeed if you have unexpected setbacks such as disease in your tomatoes or cool temperatures.
In some climates, however, planting early can be discouraged by the cooler temperatures of the spring season.
Tomatoes, as a warm-weather plant, prefer to germinate in soil temperatures of 65°F to 85°F and won’t sprout at all in soil temperatures outside the range of 50°F to 95°F. This issue is easy to resolve by sprouting your tomato seeds indoors.
As a rule of thumb, you should germinate your tomato seeds six weeks before the last chance of frost and transplant the sprouts three weeks after the last chance of frost.
In other words, your tomato sprouts will stay indoors for approximately nine weeks before being transplanted into the garden.
As with the first frost dates, you should determine the last frost dates for your region. You should then determine a date 42 or more days before the last frost date noted and plan to germinate your tomato seeds on that day.
When you start the tomato seedlings, it’s worth noting that you can use either artificial or natural lighting to give them the sunlight they need.
If you get enough sunlight, you can easily place your tomato seed trays on or beside a windowsill (but watch out for cold drafts). If the days are short, grow lights can provide the perfect sunlight for your young tomato plants to thrive.
In my personal experience, grow lights are best and worth buying for starting strong and hardy seedlings indoors.
Before transplanting your vulnerable sprouts into the garden, it’s essential to watch the weather and ensure that no unexpectedly cold temperatures arrive later than usual.
The frost dates are only averages; if a freeze happens after transplantation, you may lose some or all of your tomato plants.
Harden Off Plants Started Indoors
Before you transplant your tomato plants outside, a great way to reduce the risk of losing any of your plants is by hardening them off.
This process involves repeatedly and briefly exposing the plants to cool temperatures to encourage hardiness.
The ideal way to harden off your tomato plants is by exposing them to a temperature of 50 degrees F for several weeks.
During this time, they should be given adequate sunlight, water, and nutrition, and temperatures below 50 degrees F should be avoided under all circumstances.
Due to the prolonged exposure to cool temperatures, the tomato plants will be encouraged to change their growth to help them survive.
The hardening off will quickly result in root, branch, and stem development, making the plant significantly harder. Over time, it can result in improved yield and incredible cool temperature resistance.
Should I Cover My Tomato Plants?
The damage that cold temperatures cause to tomato plants and harvests can be drastic.
In the best cases, it can cause unsightly scarring on the fruit and a reduced yield for the tomato crop. At worst, freezing temperatures can kill your tomato plants and uproot your plans altogether.
Therefore, it’s essential to consider different methods of combating the cold.
There are several ways you can protect your tomato plants from the cold.
One of the most common methods is using row covers, which can lend 3 to 5 degrees Fahrenheit protection against the cold.
While row covers aren’t effective at protecting your plants in prolonged freezing temperatures, they can be an effective way to mitigate the damage from a short frost.
If the temperatures dip very low one night, row covers can be the protective tool that will save your plants.
You can even combine the row covers with other methods of temperature protection to ensure that your tomato plants survive the cold and ultimately offer an incredible harvest.
As a rule of thumb, you should use row covers on your tomato plants if the temperatures dip below 55°F.
But if it is a particularly long and harsh cold season. In that case, alternative methods to protect your tomatoes, such as harvesting them early or using more drastic measures to control the ideal temperature around your plants, are worth considering.
Cloches can also be used to protect your tomato plants against the cold. While they were traditionally made from glass, they can easily be made at home from bottles.
After removing the bottom of the bottle, the remaining piece can be placed on the plant. And if the temperatures get hot, you can remove the lid from the bottle to ventilate.
If the temperatures get extremely low, such as below 27°F, other ways of completing the harvest are worth considering.
Harvesting the tomatoes early and allowing them to ripen in the warmer temperatures indoors may ultimately offer a better yield than allowing the fruits to freeze and scar outside.
Should I Use A Cold Frame Or Greenhouse To Protect My Tomato Plants?
Cold frames are a type of structure that can be used to keep your tomato plants warmer and can be combined with other strategies to confer a tremendous amount of temperature protection.
Cold frames are typically made of wood, with a glass ceiling that allows sunlight in. These structures trap warm temperatures inside, which makes them significantly more suitable climates for tomatoes grown in cold regions.
They use the same principle as greenhouses to warm up but are smaller and thus easier to build and move.
Greenhouses are an even better way to protect your tomatoes in a cold climate and can be built at home or purchased pre-made.
These structures are highly effective at trapping warmth inside and will be extremely effective at helping your tomato plants survive even the coldest temperatures.
With cold frames and greenhouses, it’s essential to use a thermometer to measure whether the structure is keeping your tomato plants adequately warm.
Regardless of your strategies to keep your tomato plants warm, your plan must be well-rounded. There are many unexpected setbacks in gardening, whether a late frost or accidentally leaving the greenhouse open.
Unfortunately, many of these setbacks can ruin a harvest. But by combining strategies to combat the cold, you’ll have a well-rounded approach that will help you get the yield you deserve.
How To Speed Up Ripening
As the temperatures drop, you may still have tomatoes ripening on the vine.
Yes, there are ways to speed up the ripening process and I have an entire article dedicated to that topic: How To Speed Ripen Tomatoes Before The First Frost & Cold Weather.
More Tomato Articles:
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