Best garden covers for freeze protection

Oklahoma City’s latest freeze date on record is May 3. That record may not have fallen in the city last night, but if you think my garden didn’t suffer a late freeze, just look at this ice. It covered the outside of the plastic tunnels I used to protect my most tender plants.

Ice from the top of the row covers
Think it wasn’t cold here last night? This is ice from the top of some of the row covers.

As I wrote in my last post, a lot of the garden has achieved a certain hardiness and shrugged off a low of 31°F or lower. Perennials, shrubs and trees look great. However, I’d planted a lot of tropicals like tomatoes, coleus, alternanthera and tropical hibiscus ‘Haight Ashbury.’ Also, several of my tender bulbs had already broken the surface and were steadily growing. While I wasn’t worried about the cannas, I didn’t want to lose my dahlias so I covered them.

Plastic row tunnels with wire inserts make good freeze covers.
Plastic row tunnels with wire inserts are easy to cover a large area. They also don’t blow away.

I missed a section of the garden that faces the street, and it braved 40°F and below the night before and most of yesterday with the wind blowing. This showed a real test of those tropical plants hardier than others. I did cover this section last night, but I lost two of my favorite coleus that are new for 2013. Look at how sad this one is.

Under the Sea coleus not covered by the best freeze covers.
Under the sea coleus killed by the frost

Oh well, I know where they sell them so I’ll head back to Oklahoma City to buy three more. It was a pricey mistake, but I want those coleus in my garden. Some tropical plants like Ruellia elegans, Brazilian petunia, were fine at 40°. I did get them covered for the 31° low last night.

I only used row covers where I had a lot of space involved. For single plants, plastic pots are great.
I only used row covers where I had a lot of space involved. For single plants, plastic pots are great.

I didn’t intend to test freeze coverings, but I had so much to cover I used everything I had. With all freeze protection, you need be make sure of two things. First, plant material shouldn’t touch the top of the cover where it is coldest. This may not always be possible to keep from happening, but I did my best. Second, your covers need to stay in place all night. That may sound simple, but it’s not when the wind is blowing for all its worth. Most of these late freezes in prairie states occur during a storm, or right after, so wind is usually a factor. JWALT TunLcover Superior Plant Protectors like those shown in the photos stay in place because they have wires that go into the ground. They are fast to install and keep things pretty toasty. However, they are also pricey so I don’t have as many as I’d like. They are reusable and strong, but make sure you let them dry out between coverings. You don’t want smelly plastic with bacteria covering young plants.

Glass cloche covering a dahlia. It gets hot under there so remove as soon as possible.
Glass cloche covering a dahlia. It gets hot under there so remove as soon as possible.

Glass cloches also work well, but they are very expensive and break easily. They are, however, often used in magazines and books because they paint a pretty picture.

Gail from Clay and Limestone suggested I create a teepee from rebar and/or plastic stakes in my containers and then wrap this structure in tablecloths. By draping and placing containers up against each other to hold the coverings in place, I saved every plant. I also put containers against the house to absorb more heat. I discovered flannel-lined, plastic tablecloths are the best for this purpose. They hold in heat better than anything else I tried. They also didn’t blow off as easily, and their plastic covers shed rain. I forgot to take a photo of the teepees. I’m sorry, but you get the mental picture, right?

I also wound tablecloths through wire tomato cages to cover the tomatoes. I have nine tomatoes planted, and covers blew off three the first night when it was 40°F. I covered them again the next day. We’ll see what damage was done. Here, I found the Dalen HG25 25′ X 5′ Harvest Guard Row Cover performed really well, keeping everything toasty and remaining attached to the tomato cages. It looks like old-fashioned interfacing. You could go to a fabric store and see if something similar is available. It may or may not be cheaper.

Tablecloths drying in the sun. I'd already taken them off of the tomato cages. They were soaking wet from rain.
Tablecloths drying on the wood rack. I’d already taken them off of the tomato cages. They were soaking wet from rain.

I covered the remaining plants with plastic pots as you can see below. No, it’s not pretty, but your garden doesn’t know it looks like a junkyard. It’s a great way to repurpose and up-cycle all of those plastic pots you have in your garage. Here’s what I discovered about these pots. If you have the thinner one-gallon sized containers instead of the thick ones, stack two together and then place it over the plant. The extra air between the containers along with the extra thickness provide better insulation.

Plants were covered in everything I could find.
Plants were covered in everything I could find.

Whatever you use, the temperature warms up quickly with all that bright sunshine. Watch your weather forecasts. As long as the storm is blowing, keep things covered. If temperatures warm into the 50s, uncover everything. I usually watch for the mid-40s. You don’t want your plants to overheat after suffering such a trial. That’s insult to injury.

To recap, I found that large, plastic buckets–including five-gallon types–along with insulated, plastic tablecloths protect best. The plastic and wire-frame tunnels are great though for larger areas. Be sure to tuck in the ends so cold winds don’t simply blow through your tunnels.

This should be our last freeze, but at my house, I’m watching for that 40° benchmark. I will cover the other coleus and alternantheras if that happens, along with the new Senorita Blanca cleome in one container. They are too precious to replace. We’ve never had a freeze any later. However, Arkansas never had snow in May before either.