When winter sets in, frost can be the hour of reckoning for gardeners. It's that moment when the plants that have adapted to your local climate are going to be fine (even if a bit unsightly because they are shutting down until spring), while others will suffer, even die, without protection because they are not cold-hardy in your zone.
Shrubs wrapped in burlap are a common sight in winter across yards, but the question is: Do you really want to go through that effort year after year? For anything that you permanently plant — all the perennials, that is — you should only pick plants adapted to your USDA Plant Hardiness Zone. But that's probably not what you want to hear when you are worrying whether the beautiful crape myrtle you planted in your front yard last spring will make it through the New England winter.
Plants that fit your hardiness zone are not usually harmed by frost and chilly winter weather. There are, however, exceptions. In a warm spell during the winter, which isn't as much of a rarity with climate change, fruit trees such as apples, or ornamental flowering trees and shrubs that are normally perfectly adapted to cooler climates might be tricked into budding way too early. When the weather reverts back to more normal winter temperatures, the buds get zapped, and the flowering fruit buds are lost for the year. Because it's impractical to wrap an entire tree or large shrub in burlap, there is sometimes nothing you can do to prevent this from happening.
The first step in protecting your plants from frost is to find out which plants you really need to give extra attention to when temperatures fall below freezing — and then figure out what you can do to protect them.
How to cover plants against frost
If you live in a cool climate, all frost-sensitive container plants should be brought inside for overwintering before the first strong fall frost. If you live in a warm climate with only occasional night frosts, keep watching the weather forecast and line up everything you need to protect your plants from frost (see below).
For larger plants, cardboard boxes such as those used to package furniture or large appliances are ideal (and worth storing for this purpose if you have the room). The cardboard box should be large enough so the entire plant fits inside without breakage.
If you have a bunch of smaller pots, you can gather them under your patio table and create a "plant cave" by covering the table with old blankets and bed sheets on all sides. For just a couple of small plants, a patio chair or bench turned upside down and covered with a blanket or a sheet provides similar frost protection.
The material you use to cover your plants should be a breathable fabric or burlap, and it must be removed the next morning, so the plants aren't deprived of light. Plastic is not recommended because it prevents air circulation and traps moisture, which is a breeding ground for plant diseases. Also, if you don't get around to removing the cover promptly the next morning, and the sun hits the plastic, it can overheat the plant and scorch its leaves.
Covering plants against frost can only be a temporary remedy, though. If daytime temperatures consistently drop below freezing, bring all your potted frost-sensitive plants inside.
The last hurrah for tomatoes
If you still have tomatoes, peppers, eggplant, or other frost-tender crops growing in your garden, you can protect them with a circular fence made of bubble wrap and held in place by four stakes around the plant. Make sure to remove the plastic promptly the next morning.
While this little trick will extend your gardening season a little, the truth is these frost-tender annual plants are at the end of their lifecycle anyway — and it's time to let them go (don't forget to do a good cleanup and remove the all the dead plant material to prevent disease from spreading in your garden next year). If there are still a lot of unripe tomatoes or peppers on your plants, you are usually better off ripening them indoors.
Remember that some garden crops, such as broccoli and kale, are actually frost-hardy, so you don't have to worry about them.
Tuck in your strawberries for the winter
A winter wonderland of snow is surprisingly the best thing that can happen to your yard because when cold-hardy plants are buried under a thick snow cover, they are actually insulated against the cold. It's when plants are exposed to chilling winter winds that the most damage occurs, even to plants that are otherwise fully winter-hardy.
Strawberries are the most notorious for suffering winter damage in the absence of snow. That's why I covered my strawberry patch on our wind-beaten hilltop in northeast Pennsylvania with a thick layer of straw a few days ago. I'll leave the straw on until early spring when the strawberries start growing again.
Time to get digging
If you've already had frost in your area, your gladiolas, dahlias, and cannas will likely have died back. That's nothing to worry about as they only die off above ground; the roots and tubers in the ground are still alive. Still, they should be dug out and stored inside in a cool location for overwintering before a deep frost, and well before the ground freezes.