Using Frost Blankets to Protect Plants from Freezing

It can be worrisome when you see the forecast predicting unusually low temperatures when your landscape plants have already leafed out. Some may even be in full bloom! How can you protect your plants against frost?

One solution is using frost blankets.

A frost blanket is simply a lightweight, white, woven material that is manufactured specifically to cover plants. You might have heard the term, “floating row cover,” which is essentially the same thing.

Farmers have used them for years to protect their crops flowers and keep insects from eating their plants. We can use them in our yards, too.

How frost blankets work.

They protect plants from frost by trapping the heat that radiates from the soil.

The soil is warmed by the light energy from the sun. Some of that heat radiates out of the soil into the atmosphere. Without a frost blanket, the heat dissipates into the surrounding air. But if the frost blanket is creating a tent over the soil, some of that heat will be trapped by the blanket. This will create a pocket of warmer air, which can temporarily keep your plant from freezing.

Think ghosts, not lollipops.

Because frost blankets trap the heat radiating from the soil, you have to use them like a tent. When I’ve covered several plants in a landscape, it looks like ghosts are haunting the place. That’s good because the frost blankets can create a pocket of warm air.

If you gather up the ends and tie them to trunk above the soil like a lollipop, the blanket can’t trap the heat from the soil. The result is that the heat radiates around the plant and the blanket doesn’t work. So when you’re covering plants with frost blankets, make them look like ghosts, not lollipops.

Here’s a picture of a barberry plant that had just leafed out. The weather forecast predicted a low of 22 degrees.

Here’s how it looked after I covered it with a frost blanket. Notice I taped the blanket to the pot to create a pocket of air, not to the shrub’s trunk.

Frost blankets much better than old sheets for several reasons.

They are lightweight, so they don’t crush plants.
They let light through, so you can leave them on for several days.
It’s easy to cut them with scissors to customize the shape.
Air is able to pass through the fabric, allowing your plants to “breathe.”
It’s easy to secure them using duct tape or landscape fabric pins.
The thinner ones let water through as well, so you can leave them on for several weeks.
They’re reusable and easy to fold up and store.

If you have an area that doesn’t fit the shape of your frost blanket, simply use a pair of scissors to cut it to the right shape. I cut this blanket to fit around this curved edge.

How do you keep frost blankets in place?

The nice thing about frost blankets is that you can use duct tape or landscape fabric pins to keep the fabric in place.

Duct tape can secure the blanket to a pot or another hard surface.

Or you can tape the fabric to itself to create a pocket of air.

In areas where you want to secure the fabric to the soil, simply use landscape fabric pins. It will easily puncture right through the fabric and stick into the soil. Here’s what it looks like when the pin is partially pushed in.

Here’s what it looks like when the pin is pushed all the way into the soil.

Here’s a picture of the label of the brand that I typically use. I buy them at my local nursery in the 10 x 12 feet size. This brand has worked well for me along Colorado’s Front Range.