Preparing for Fall Frost
By the time fall frosts threaten, sometimes I think I am ready to be done with growing. But no, every time at the last minute I do what is necessary to save my plants. After all, there is still plenty of nice weather left to enjoy them, especially unharvested produce!
So now, how to prepare?
First, know that air temperatures are taken several feet off the ground. Since cold air settles it will be at least a few degrees colder around your plants than the forecast air temperatures. This is why you see frost warnings when the forecast temperatures are well above the freezing point.
Make sure you go into a frosty night with moist soil, it will hold the heat better.
Determine which plants are most susceptible to frost. The Early Spring Planting article lists plants that are tolerant of varying degrees of frost.
Determine which plants are most dear or valuable, or most tender, and be sure to give those plants top priority.
Recently planted perennials may not be established enough to survive a frost yet on their own, so plan to protect them.
If you pruned or fertilized perennials or shrubs too late in the season new growth may still be maturing and will be more susceptible to frost.
Gather protection materials to have ready on a moments notice.
What are the best protection materials and methods?
Plants in pots or containers can easily be moved to a location that offers protection from frost. Inside a garage or shed is easiest but not always possible. Since cold air settles to the soil surface, placing all your container plants up on a raised deck or patio is helpful. To prevent any cold air from settling into the pot, place the containers under an overhang if you can. Placing containers up agains a warm building can also be helpful. Grouping all the containers together in a tight cluster can also help to retain heat by trapping the warmth between the containers.
For plants in the ground you should devise a frost protecti on method that is easy for you to put in place, ideally with materials that you have readily available. whatever method you devise should create a “bubble” of warm trapped air around your plants by covering them. A cover will prevent the cold air from settling on and around the plants. A cover that reaches the ground all the way around the plant will also trap heat around your plant. Avoid having the cover come in contact with the plant itself, as the cold will transfer through the material to the plant.
If you plan to use sheets, blankets or purchased frost cloth or seed blankets, you will need some sort of framework to surround the plants and drape the cloth over. Be sure the cover puddles over the ground and anchor it to the ground or your framework to prevent breezes from moving it. I use old tomato cages for frames, clothespins to close gaps and pin to the frame, and rocks to anchor the fabric to the ground.
Avoid using sheets of plastic if you can. Plastic does not breathe and traps moisture inside your bubble. If you must use plastic be sure to remove it as soon as it begins to warm up a bit the next morning.
If you have a fenced garden you can cover the whole thing by tightly clipping together sheets or blankets and use the fence to support and anchor the cover. If your plants are taller than the fence, push a few tall garden stakes into the interior of the garden to hold the fabric above the plants.
Cardboard boxes are excellent covers also. They are frame and cover all in one, they allow air circulation and they “breathe”, and are very easy to slip over plants. Anchor them by placing something heavy on extended flaps.
Plastic buckets can be used similarly to cardboard boxes. If they are heavy enough only a good wind will remove them, but you should use landscape fabric pins to anchor the bucket handle to the ground or just put a heavy rock on top of the bucket. A plastic bucket does not breathe like fabric or cardboard, so be sure to remove them as soon as it begins to warm up the next morning.
These methods offer good protection from light and heavy frost, and should protect quite well against at least a light freeze. If your most tender plants get nipped, or if you failed to secure your covers well enough, your plants may recover. Just leave them be for a couple of days or so to see how the damage develops. Frost damaged limbs often discolor or turn dark, or simply shrivel and get limp. Then prune off any dead or severely damaged limbs. Do not fertilize frost damaged plants, that will only encourage new growth that will be even more susceptible to frost.
Learn more about frost prevention by learning about microclimates.