Frost cowl: safety for crops

If you live in a region with distinct seasons, you have been developing strategies for some time to protect plants from the cold. But if you're like me and live in an area that is increasingly fraught with cold weather in the wintertime with climate change, you may have improvised. Whether or not you have experience with wintering your garden or not, a blanket of frost is something useful to have on hand.

Frost blankets come in many different forms. Commercial products are great, but there are tons of options outside of products labeled "Frost Blanket". Knowing your material will tell you what to do when it gets cold and what to do when the heat rises again. And you protect your plants in the process.

Frost protection is important in areas where winter doesn’t come out. Here in Texas, for example, we recently saw extreme shifts of 30 degrees Fahrenheit in just an hour. This is a lot of stress for the plants. But with the right frost cover, I've managed to keep things healthy.

And you can do that too! Now that you've watered your plants before freezing, let's talk about blankets of frost in all of their shapes and functions. Then you can decide what is best for your situation.

What is a frost blanket?

The term “frost cover” describes a category of plant protection options. Source: Baugher

A frost blanket is a cloth, plastic, or other material that is used to cover plants when it's cold. There are several types of frost protection blankets, some for protecting plants and others for protecting plants in a home garden. Some are easy, some are harder. Some are made commercially and specialized, while others are made from things lying around the house. They are designed to protect the delicate leaves of the plants from the cold so that they can survive winter and snow. Sometimes they are called floating row covers. The difference between frost blankets and floating blankets is significant, so we have dedicated a section of this article to explaining the differences between them.

How frost blankets work

Young plants under a blanket of frostTender seedlings need more protection than established plants. Source: Peganum

Frost blankets work in different ways depending on where they are used. When shopping online for a commercial frost blanket, you have options for both floor and raised bed solutions. Let's talk a little about the differences there.

In the ground

The earth will always be warmer than the air because the water molecules in the earth warm the soil and help it retain some heat while the air freezes. While this is the case, plants can suffer cold damage if planted in the ground and exposed to frost. Because of this, you want to find something that will protect your plants without touching them.

Raised beds

Above-ground beds tend to stay warmer in freezing temperatures and thaw more quickly. They also make it easier to create a bed-specific row cover system. Even though there is built-in protection in raised beds, the longer the frost lasts, the longer they are at risk of damage. Correct application for covering plants is important. One thing I've learned is that if your plants are small enough to sit under the top of the raised bed, a simple sheet or suitably attached blanket will do. If you've built a raised bed hoop house, you can use this frame for taller plants as well.

A word of support

One thing that you will need regardless of the shape of the frost blanket is some sort of support to keep the blanket material away from the leaves of plants or crops. Light becomes trapped in it and bounces around, increasing the temperature when it interacts with the warmth of the ground. In the sun, the temperature under your blanket of frost can be 30 to 50 degrees warmer than outdoors. If you are using plastic, this difference is in the upper range. Plants that are under a blanket of frost at 50 degrees can be fried if they touch greenhouse plastic or even an old bed sheet. Putting plants in this situation after experiencing a cold spurt will tax them unnecessarily.

Unless the frost cover you are using has no built-in supports, design your own. I live in a back yard with tons of bamboo so bamboo stakes hold my frost blanket. PVC pipes can be made into tires, and a tire house can be your antifreeze. Even branches and sticks, wooden stakes or dowel rods work. Whatever you can get your hands on to keep the cloth or plastic off your plants is great. Supports also lift the frost blankets above the ground, trapping heat and moisture inside. Good supports protect your plants from longer periods of cold and frost. Tire houses and framed shelter are great for people who experience arctic winters.

Types of frost cover

Roll of frost fabricCommercial frozen materials are sold in small or large quantities. Source: clements.evan

As we discussed, there are many options when it comes to frost blankets. Commercial retailer frost blankets are designed to lock in the heat you need to protect your plants without all of the fuss and hassle of homemade methods. However, using a blanket or sheet to cover plants can be virtually free for some.

Commercial frost blankets

In general, commercial frost blankets are made from woven polypropylene fabrics of varying weights that cover plants in snow and ice. In early spring, lighter versions are sometimes used as row protection during light and late frosts. They are also used to keep insects and birds away from young crops and plants that may be establishing themselves for the first time in a season. Thicker versions, however, are not suitable for light frosts and insect and bird invasion as they don't let enough light and air through to keep the plants healthy. Lightweights are better for a cold snap or a quick winter storm.

Some commercially available frost blankets are openly woven fabrics, others are plasticized. Plastic anti-freeze blankets trap much more heat than fabric blankets. Don't forget to take them off when the sun rises and the temperature rises so you don't cook your plants or crops.

Sheets and blankets

The downside to commercial options is that they can be expensive and sometimes orders placed online don't arrive on time. If commercial frost blankets are not an option for you due to financial or time constraints, fabric bed sheets and blankets are a suitable substitute. They do the basic things you need a frost blanket for: they protect your plants from frost, trap heat from sunlight, and help the soil hold in moisture. They are not as permeable as standard frost blankets made of lighter fabric, but they do not trap as much heat as plastic. All you have to do with them is spread them on and around supports next to your plants. And while they don't hold as much heat as plastic, they should also be removed when the temperature rises. Be warned, these can be heavy enough to keep sunlight from reaching your plants!


Canvas is another option. If you have a roll of canvas lying around for painting or doing handicraft that requires a cloth, you can roll some of it out for your plants. While this is a viable fabric option, it doesn't offer as much protection as a commercially available frost blanket or close-knit sheet. Canvas material is not woven as tightly and can let in a little more cold. However, if this is your only option, it will protect plants in a situation where you need something quickly. Although it is permeable, it should be removed when the lights break for the day and the temperature rises. Canvas can become very heavy when wet and lets almost no light through the plants.

To plan

Tarpaulins can also be used to protect a plant from frost. However, they are not that great in the long run. Use a different material for long-term situations. Tarpaulins are not designed to protect plants in frosty weather and can actually transfer freezing temperatures to plant tissues. Plants under a tarpaulin do not get the same protection as a frost blanket or even a normal blanket. However, tarpaulins can be used to protect fabric covers from melting snow. Instead of melting snow right on your fabric sign and distributing that cold onto your plants, the tarpaulin lets the water roll off. So use them as an addition to your homemade fabric frosted blanket.

Greenhouse plastic

The great thing about greenhouse plastic is that it can withstand direct sunlight, heat, and frost. Unlike a tarpaulin, greenhouse plastic protects plants and captures the light needed to keep them healthy over long-term winters. Greenhouse plastic is particularly useful in conjunction with tire houses. You can find it almost anywhere from a tractor accessory store to a wholesaler. Some greenhouse plastics come in a kit that you can install before winter. Some come in individual sheets that you can cut to size. Growers who are used to dealing with the elements know the power of this material. However, be aware of the heat in your plastic protector. This material is easy to buy, install, and manage, but expect the upper end of the air temperature to rise when the sun hits it. Remove it prudently, and you could swear by it (like me!).

Floating row covers

Protection of endangered plantsYou may just need to protect some delicate plants. Source: Karen Roe

Simply put, a floating row cover is a frame with a frost blanket that you can remove and replace as needed during the cold season. This could be a setting for your garden. These can be tires that you can put over your raised bed, or some kind of frame with frost cloth or plastic over them. The same rules apply to floating covers: too much heat puts unnecessary stress on your plants, so move them around as soon as it gets too warm.

When it comes to floating fabric covers, the following applies: the lighter, the better. Especially in small gardens where a floating form of protection might be excessive, you want something gentle on your and your plants. Sometimes heavy fabrics or plastic not only put a strain on your plants, but can also put a strain on them if you try to move and remove them. If you are going to buy one you need to know the size in advance. However, you could make your own instead of opting to buy. Tires are very easy to make, assemble and reassemble if necessary. Wooden frames may be too heavy, but for row crop growers, the heavy option may be easy and best. As long as you are loading something heavy with a little help, loading a frame may be the best option for keeping the air around your plants warm.

Other frost blankets

Some materials have amazing uses when it comes to frost blankets. Acrylic floss tied to trees is a simple, inexpensive solution that growers can use in a pinch. Once you've calculated the spacing between your trees, you can buy acrylic fabric this size plus quite a bit to cover your plants for a day or so. The wadding (or fabric) keeps the air inside warm and forms a suitable frost cover where, because of the trees, no stakes are needed. The acrylic fabric could be too much for an early spring frost when the air isn't so freezing cold that you need a tightly closed blanket.

"Plankets" or similar frost bags are a new form of fabric protection for a plant in the cold season. These are specially designed to trap warm air and protect plants from frost. They have a cinch cord included in the fabric that makes it easy to attach to almost any frame or plant. Plankets are also great fabric options for a pot plant. They are easy to install and remove. The fabric is light and breathable. If you are looking for a cloth towel to protect crops from frost, this is a great option.

frequently asked Questions

Garden frost protectionThe garden frost protection ensures the safety of your plants. Source: CAJC in the PNW

Q: What can I use as a frost blanket?

A: Frost blankets can be anything from old blankets and sheets to specialty greenhouse plastic and commercial frost blankets. You will need stakes to keep the leaf off your yard as well.

Q: Can you keep frost blankets on during the day?

A: Assuming it's freezing, yes. Note, however, that the temperature in thick blankets of frost can be between 30 and 50 degrees warmer than outside. Use with caution.

Q: Are frost protection blankets working?

A: They do! Sometimes too good, though some are better than others for long-term situations, and some are better for just a night or two.

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