Gardening Tips, Projects

Frost Blanket: Protection For Plants


Frost blanket

If you live in a region that has distinct seasons, you’ve developed strategies for protecting plants from the cold for some time. But if you’re like me, and you live in an area that increasingly gets hit with cold weather in the winter as the climate changes, you may have been improvising. Whether you’re experienced with winterizing your outdoor garden or not, a frost blanket is something useful to have on hand.

Frost blankets come in many different forms. Commercial ones are great, but there are tons of options outside of products labeled “frost blanket”. If you know your material, you’ll know what to do when the cold hits, and how to adjust when the heat rises again. And you’ll protect your plants in the process. 

Frost protection is important in areas where the winter does not mess around. For instance, here in Texas, we’ve recently experienced extreme shifts of 30 degrees Fahrenheit over a course of just one hour. That’s a lot of stress on the plants. But with the right frost blanket, I’ve managed to keep things healthy. 

And you can too! Now that you’ve given your plants water ahead of the freeze, let’s discuss frost blankets in all their forms and functions. Then you can decide which works best for your situation. 

What Is a Frost Blanket?

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

A frost blanket is a sheet of fabric, plastic, or other material used to cover plants in cold. There are different types of frost blanket, some designed to protect crops, others designed to shield plants in a home garden. Some are light-weight, while others are heavier. Some are commercially produced and specialized, while others are fashioned from things lying around the home. They are meant to keep the tender leaves of plants out of the cold so they survive winter and snow. Sometimes they’re called floating row covers. The difference between frost blankets and floating covers is significant, so we’ve devoted a section of this piece to explaining the differences between them. 

How Frost Blankets Work

Young plants under frost blanket
Tender seedlings need more protection than established plants. Source: peganum

Frost blankets function in different ways depending on where they go. When you shop online for a commercial frost blanket you will have options for both in-ground and raised bed solutions. Let’s talk a little bit about the differences there. 

In-Ground

The earth will always be warmer than the air because the water molecules in the earth heat up the soil, and help it retain some warmth while the air freezes. Although this is the case, plants can still take cold damage when they’re planted in the earth and exposed to freezing weather. For that reason, you want to find something that can guard your plants without touching them.  

Raised Beds

Above-terrain beds tend to stay warmer and thaw faster in a freeze. They also make it easier to make a row cover system specific to the bed. Even though there’s built-in protection with raised beds, the longer the freeze lasts, the longer they are in the range of being damaged. Proper applications to cover plants is important. One thing I’ve learned is if your plants are small enough to sit below the top of the raised bed, a simple sheet or blanket over the top affixed appropriately suffices. If you’ve built a raised bed hoop house, you can use that framework for taller plants too.

A Word On Supports

One thing you will need no matter the form of frost blanket is some kind of support to keep the material of the blanket away from the leaves of plants or crops. Light gets trapped within and bounces around increasing the temperature as it interacts with the warmth of the soil. In the sun, the temperature under your frost blanket can be anywhere from 30 to 50 degrees warmer than it is outdoors. If you’re using plastic, that difference is on the higher end. Crops that are under a frost blanket at 50 degrees could be fried if they’re touching greenhouse plastic or even an old bedsheet. Putting plants in this situation after they’ve experienced a burst of cold taxes them unnecessarily. 

Unless the frost blanket you’re using has built-in supports, fashion your own. I live in a backyard with tons of bamboo, so bamboo stakes hold up my frost blanket. PVC pipes can be fashioned into hoops, and a hoop house can be your frost protection. Even tree branches and sticks, wooden stakes, or dowel rods work. Whatever you can get your hands on to keep the fabric or plastic away from your plants is great. Supports also raise the frost blankets above the earth, trapping heat and moisture inside. Good supports protect your plants through extended periods of cold and frost. Hoop houses and framed protection are great for people who live through arctic winters. 

Frost Blanket Types

Roll of frost fabric
Commercial frost fabrics are sold in small or large quantities. Source: clements.evan

As we’ve discussed, there are many options when it comes to frost blankets. Frost blankets from commercial retailers are designed to trap in the heat you need to protect your plants, without all the fuss and finagling of homemade methods. However, using a blanket or sheet to cover plants can be virtually free for some. 

Commercial Frost Blankets

Generally, commercial frost blankets are woven polypropylene fabric in varying weights that cover plants in snow and ice. Sometimes lighter versions are used in early spring as row protection for light and late frosts. They’re also used to keep insects and birds out of young crops and plants that may be making their first foothold in a season. Thicker versions aren’t suited for light frosts and invasions of insects and birds, though, because they don’t allow enough light and air through to keep plants healthy. Lightweights are better for a cold snap or a quick winter storm. 

Some commercial frost blankets are open-weave cloth, and others are plasticized. Plastic frost blankets trap in much more heat than fabric ones do. Don’t forget to take them off when the sun rises and the temperature increases so you don’t cook your plants or crops. 

Bed Sheets and Blankets

The downside of commercial options is they can be expensive, and sometimes orders made online don’t arrive in time. If commercial frost blankets aren’t an option for you, whether due to financial considerations or timing, fabric bed sheets and blankets are a suitable substitution. They will do the basic things you need a frost blanket to do: they’ll protect your plants from frost, trap in heat via sunlight, and help the soil maintain moisture. They aren’t as permeable as lighter fabric commercial frost blankets, but they don’t trap in as much heat as plastic. All you have to do with these is spread them across and around supports next to your plants. And although they don’t trap as much heat as plastic, you’ll want to remove them when the temperature rises too. Be forewarned, these may be heavy enough to prevent sunlight reaching your plants!

Canvas

Canvas is another option. If you have a roll of canvas lying around for painting, or doing manual labor that requires a drop cloth, you can roll some of it out for your plants. While this is a viable fabric option, it doesn’t provide as much protection as a commercial frost blanket or a tightly knit sheet. Canvas material isn’t woven as tightly and can allow a little more cold in. Still, if this is your only option it will protect plants in a situation where you need something quickly. Although it’s permeable, it should be removed when the light breaks for the day and the temperature rises. Canvas can get very heavy when wet, and allows almost no light through to the plants.

Tarps

Tarps can also be used to protect a plant from frost. However, they aren’t great long-term. For long-term situations, use another material. Tarps aren’t created to protect crops in frosty weather, and can actually transmit freezing temperatures to plant tissue. Plants under a tarp won’t get the same protection as they would from a frost blanket or even a regular blanket. Tarps can be used to protect fabric covers from melting snow, however. Instead of snow melting directly onto your fabric shield, and spreading that chill to your crops, the tarp will allow the water to roll off. So, use them as a supplement to your homemade fabric frost blanket. 

Greenhouse Plastic

The great thing about greenhouse plastic is it is designed to withstand direct sunlight, heat, and frost as well. Unlike a tarp, greenhouse plastic will protect plants, and trap in light needed to keep them healthy in long-term winters. Greenhouse plastic is especially useful in conjunction with hoop houses. You can find it almost anywhere, from tractor supply stores to big-box distributors. Some greenhouse plastics come in a kit that you can install ahead of the winter. Some come in single sheets you can cut to the right size. Growers used to dealing with the elements are well-aware of the power of this material. However, one thing to pay attention to is the heat inside your plastic protector. This material is easy to buy, install, and manage, but you should expect the higher end of air temperature to increase when the sun hits it. Remove it in a calculated manner, and you might swear by it (like I do!).   

Floating Row Covers

Protecting vulnerable plants
You may only need to protect a few vulnerable plants. Source: Karen Roe

Put simply, a floating row cover is a frame with a frost blanket that you can remove and replace as needed throughout the chilly seasons. This could be a frame for your garden. These could be hoops that you can place over your raised bed or some kind of frame that has frost cloth or plastic over them. The same rules go for floating covers: too much heat taxes your plants unnecessarily, so move them as soon as it gets too warm. 

One thing to remember with fabric floating covers is the more lightweight the better. Especially in small gardens, where a floating form of protection might be overkill, you want something easy on your and your plants. Sometimes heavy fabric or plastic not only taxes your plants but can put a strain on you when you try to move it and remove it. If you want to buy one, you have to know the size ahead of time. You could make your own instead of opting to buy, though. Hoops are very easy to make, assemble when needed, and reassemble. Wooden frames might be too heavy, but for growers with row crops, the heavy option might be easy and best. As long as you’re loading something heavy with some help, loading a frame might be the best option to keep the air around your plants warm. 

Miscellaneous Frost Blankets

Some materials have startling applications when it comes to frost blankets. Acrylic batting tied to trees is an easy, low-cost solution that growers can employ in a pinch. If you’ve calculated the distance between your trees, you can purchase acrylic fabric at that size plus some to cover your plants for a day or so. The batting (or fabric) keeps the air inside warm and makes an appropriate frost blanket where no stakes are needed because of the trees. The acrylic fabric might be too much for an early spring frost where the air isn’t so freezing that you need a tightly sealed blanket.

“Plankets” or similar frost bags are a new form of fabric protection for a plant in the chilly season. These are specially fashioned to trap in warm air and protect plants from frost. They have a cinch cord included in the fabric that makes it easy to affix it to almost any frame or plant. Plankets are great fabric options for a plant in a pot, too. They’re easy to install and remove. The fabric is lightweight and breathable. If you’re looking for a fabric sheet to shield crops from freezing weather, this is a great option.

Frequently Asked Questions

Garden frost prevention
Garden frost prevention ensures your plants’ safety. 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 specialized greenhouse plastic and commercial frost blankets. You’ll need stakes to keep the sheet off your garden too. 

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

A: Assuming it is freezing, yes. But note the temperature inside thicker frost blankets can be anywhere from 30 to 50 degrees warmer than it is outside. Use with caution. 

Q: Do freeze blankets work?

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

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