How to Protect Your Tomato Plants From Cold and Frost

As any gardener knows, it is easy to become over-eager and plant your garden too early. Maybe you planted your tomatoes a little early this year, and now there is danger of a late spring frost. In that case, you’ll want to find ways to keep your plants alive through the cold nights.

So, how can you protect tomato plants from cold and frost? A cloche is the best way to protect a young tomato plant from frost. Row covers are another good method to protect against frost if you have many tomato plants in a row.

There are many options for both cloches and row covers. What you use depends on your budget, the time and materials you have available, and the number of plants you need to protect.

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Using a Cloche to Protect Tomato Plants from Frost

Cold soil can cause all sorts of problems for tomato plants. For example, if the leaves of your young tomato plants start to turn purple, cold soil may be to blame.

Cold temperatures may also cause vivipary (sprouting seeds inside the tomato fruit).

A cloche is one method you can use to protect tomato plants from a late spring frost. Let’s start off with a discussion of what a cloche is, and then we’ll get into the options that are available.

What is a Cloche?

A cloche is a cover, usually clear and bell-shaped, that protects a young plant from cold, insects, and damage due to wind. There is an opening at the top that can be sealed or opened to act as a vent.

This vent allows air into the enclosure and prevents overheating. Think of a cloche as a greenhouse that only protects one plant.

Cloche is the French word for “bell”, and a cloche is usually bell-shaped or dome-shaped. A cloche can be made of glass, plastic, or wire.

You can use a longer, rectangular cloche to protect two or more plants together, but this is more like a mini-greenhouse than a true cloche.

Glass Cloche

Before the invention of plastic, a cloche was made of glass. They were used on farms in France to protect plants from cold, insects, and wind.

A cloche can protect against late spring frosts or allow farmers and gardeners to plant seeds earlier in areas with short growing seasons.

If you decide to use a glass cloche, make sure to find one with a hole in the top. This allows for ventilation so that plants do not overheat, and prevents the sun’s rays from burning plant leaves and stems.

There are some drawbacks to using glass cloches. A glass cloche is more expensive than a plastic cloche. Also, it is difficult to put holes in the top of a used glass bottle without breaking it, whereas plastic is easily pierced with a hot, thin piece of metal.

A glass cloche is more of a curiosity these days, but if you can afford them, they can give your garden a unique look while also protecting your young tomato plants.

For more information, check out this article on glass cloches from Michigan State University.

Plastic Cloche

You can buy plastic cloches online or at garden centers, for much cheaper than glass cloches. You can also make your own plastic cloches, which costs you virtually nothing.

First, gather some empty plastic bottles from the week’s groceries. If you have a large garden, ask some friends for spare plastic bottles.

Plastic gallon jugs for milk or water are great for making cloches. As an alternative, you can use a plastic 2-Liter bottle. However, these 2-Liter bottles are a bit thinner, and probably only useful for very young tomato plants that do not have large branches yet.

Plastic water jugs make for a good cloche after you cut out the bottom.

Once you have your bottles, use scissors or a knife to cut out the bottom of the bottle (the large part – leave the top part with the cap intact). You only need to remove an inch or less from the bottom of the bottle.

Now, you have plastic cloches – use one to cover each tomato plant. As an added benefit, the cap of the bottle can act as a vent.

Remove the cap in the morning, especially on hot days, so that the plants don’t overheat in the midday sun. Then, seal the cap in the evening to prevent cold nights from harming your plants.

Sometimes, you plant your garden way too early, or the cold nights persist longer than you thought they would. In that case, you may need something taller to protect more mature plants.

One option is to stack two or more of these cloches to make a taller cloche. Another option is to use row covers (discussed later).

Wire Cloche with Fabric

A wire cloche is your third option, and it has some versatility. You can keep the wire cloche on the plant during the day, to protect against larger garden pests like rabbits.

You can buy wire cloches specifically made for this purpose, or fashion your own. For instance, you can use a tomato cage as the cloche itself.

wire mesh — You can use chicken wire to fashion a wire cloche.

Then, you can put a cloth or plastic sheet over the wire cloche at night, to protect against colder temperatures and insects pests like cutworms.

Just make sure to weigh down the edges of the cloth or plastic cover with rocks, in order to prevent them from blowing away in the wind. Also, remember to remove the plastic or cloth in the morning, especially before a hot day.

If you forget to remove your plastic sheet, the plants can overheat in the sun. If you forget to remove your cloth sheet, the plants might not get the sunlight they need to grow properly.

You can also use a length of rabbit-cage wire to fashion your own curved multi-plant cloche. Just make sure to seal the ends with a piece of wood to insulate and keep pests away.

Using Row Covers to Protect Tomato Plants from Frost

If you have a larger garden with long rows, then using row covers will be less time-consuming than cloches in the long run. Let’s talk about what row covers are, along with the options that are available.

What are Row Covers?

A row cover is a sheet used to protect plants from cold, pests, and wind. Unlike a cloche, a row cover does not need a vent if the sheet is made of breathable material, such as cloth or some other fabric.

By its nature, a row cover is intended to protect more than one plant at once, although you could use a small piece of fabric or plastic to protect one plant.

A row cover can be made of fabric (such as cloth or burlap) or plastic. Generally, stakes are used to hold up the row cover over the plants, and to secure it in place against the wind or curious garden pests. However, you can also use tomato cages to hold up row covers if you decide to go that route.

For more information, check out my article on support for tomato plants and my article on why to use tomato cages.

Fabric Row Covers

Fabric row covers have the advantage of being breathable, meaning that you don’t have to worry as much about plants getting too hot underneath the cover.

Often, row covers will be made of polyester or a similar material. Two well-known brands of fabric row covers are Reemay and Agribon.

One disadvantage of fabric row covers is that they deteriorate quickly. While glass, plastic, or wire cloches can last indefinitely, fabric row covers can start to tear after one season.

This is especially true if you have a stormy, windy growing season, or if larger garden pests get curious and start disturbing the row cover.

If you use stakes or cages to support your tomatoes, you can also use them to hold up your row covers. It is a good idea to leave some clearance between the plants and the cover, so that the plant is not accidentally exposed to cold.

Plastic Row Covers

This option is likely more cost-effective than fabric row covers. First of all, you are more likely to find discarded plastic sheets than fabric row covers. Second, plastic will probably last longer than fabric row covers.

However, it is important to remember than the sun will make thin plastic brittle, and it will eventually break. Using plastic instead of fabric does not mean that you will never need to replace your row covers; it will just happen less frequently.

Aim for clear or white plastic for your row covers. Dark or black plastic can trap too much heat and kill your tomato plants, and it will also prevent them from getting the sunlight they need to grow.

You can buy plastic row covers online or at garden centers. You also have the option of perforated plastic row covers, which will allow your plants to breathe a bit more.

If your plastic covers are not perforated, remember to remove the row covers in the morning before a hot day, or else you might burn or kill your plants!

For more information, check out this article on row covers from Michigan State University.

How to Protect Raised Beds Against Cold and Frost

You can use row covers to protect raised beds as well. Simply put up tomato stakes at the four corners of your raised bed (possibly in between if the dimensions are long).

Then, secure the row cover to the stakes to cover your raised bed under a kind of tent. Again, make sure to use rocks to keep the row covers from blowing away in the wind.

What to Look Out For When Using Cloches or Row Covers

There are two things to watch out for when using cloches or row covers to protect your plants.

Allow for Pollination

Your plants need to be protected from cold and frost, but they also need pollination when they grow large enough. Be sure to remove cloches or row covers during the day to allow bees to work.

bee on blueberry flower — Bees can only work to pollinate your flowers if they can reach them!

If you don’t have many bees around, you may need to hand-pollinate with an electric toothbrush or another tool. For more information, check out my article on hand pollination for tomato plants.

Avoid Extreme Heat

Extreme heat can kill your tomato plants just as easily as extreme cold. Remember to open cloches or remove row covers to avoid overheating during the day.

Also, remember that high temperatures can prevent pollination, even if have plenty of bees or if you hand pollinate! Don’t put in all the work of protecting your tomato plants from cold, only to have them fail to produce any fruit!