When you live in a climate with real winter, frost is a fact of life. But when frost comes too early, a gardener has to take action!
What’s too early? Well, I’ve been hearing from gardening friends slightly north of me who had frost warnings in August. They were posting photos of what looked to be their entire gardens swaddled in every spare blanket they could find. If they managed to get their plants through those couple cooler nights they likely have close to another month of life in them. And that makes it worth the effort to try to protect them.
Protecting plants from frost is pretty simple—you want to cover them with something that will keep the heat, which radiates from the ground, around the plant. And, to some extent, keep frost from “settling” on the plants.
What to cover your plants with:
Old bed sheets, blankets and quilts make great covers. Burlap works well too. Commercial row cover material, which is a white filmy fabric (I have some called Agribon) also works if it’s just a mild frost. Overturned cardboard boxes make a great insulator.
What not to cover your plants with:
Plastic, including plastic tarp, isn’t a good choice to use if your plants are going to touch them. Leaves that come into contact with the cold plastic will likely suffer frost damage. If you’re expecting a really heavy frost you could cover plants with blankets first, and then layer a tarp on over top.
How to cover your plants:
*Drape a fabric cover over tender plants in the evening when frost is expected/possible.
*If the fabric is heavy or the plants are fragile (e.g. some begonias have stems so fragile they break if you look at them sideways) put some stakes in the ground or in the planter pot to support the weight of the fabric.
*If you can, drape the fabric all the way to the ground. This will help to capture radiant heat from the ground. If they’re in a pot, cover the whole pot if you can.
*If it’s a very windy night, you can use large safety pins or, my favourite, binder clips, to keep the cover in place.
*Remove the cover in the morning, once the temperature has risen out of the danger zone. I’ve read that the coldest time of night is just after dawn. If you have to leave the house early in the morning (i.e. for work) while it’s still freezing out, leave the covers in place–it won’t kill your plants to stay under the covers for a day or two. Just don’t leave them for too many days, as they do need sunlight in order to live.
What plants to cover:
When I experience an early frost, I cover my tender annual flowers (begonias, petunias, fuschias) and other decorative annual plants, especially coleus. I also cover herbs like basil and parsley, and food plants like tomatoes (which are a real challenge, as mine are usually close to 8’ tall by now), peppers, pumpkin, squash, beans and eggplant. Essentially, any plants that normally turn into a mushy mess after a frost.
I don’t usually worry too much about geraniums, rosemary and sage or root crops like carrots or beets. Turnips actually need frost in order to become palatable.
In my garden I can usually keep tender plants growing into at least the early part of October. That means I’ll be keeping a very close eye on the weather forecast for the next few weeks. If I hear it’s likely to go down to 5°C (41°F) or lower between now and then, you’ll find me hauling my old fabric shower curtains and sheets out of the shed!