Cold frames can seem like damned-if-you-do, damned-if-you-don't season extenders. By the time it's warm enough to plant, your garden beckons for your attention in every other direction. You blink, and summer's in full glory. Blink again and you're staring outside at your abandoned cold frame, where some heads of lettuce managed to rot and freeze. No more! Along with a houseful of holiday helpers, I schemed a solution to rejuvenate your winter garden and put your cold frame to work protecting tender plants until spring.
The secret? Capitalize on the forgiving nature of herbs. They'll survive a cold night, can withstand a forgotten watering or two, and will provide a perfect sparkle of green under those panes of glass. Pick a selection of cold-hardy herbs from your local nursery, scoop up some terra cotta pots, and prepare yourself to perform some sleight of hand winter garden magic.
Photographs by Erin Boyle.
Step 1: First things first. Clean off the windows of your cold frame—just like with car headlights, even a slight film will make a big difference in how much light your plants can absorb.
Step 2. Tidy your space. Clear garden residue and turn the soil lightly. It's another gift of cold frames that the ground underneath them will be frozen less solid than the rest of your garden.
Step 3: Spread a thick layer of compost, potting soil or topsoil to replenish your soil, and then dig 6-inch holes for each of your potted herbs. This will help insulate against extreme temperatures that can build up in cold frames and will make it easy for you to move them inside if the weather takes a sudden turn for much hotter or much cooler.
Step 4: Before you nestle the herbs inside the holes, you'll want to upgrade from their plastic nursery pots. I chose frost-tolerant varieties of scented geraniums, winter savory, thyme, rosemary, and marjoram—and terra cotta pots. (If your herbs are coming directly from a greenhouse, consider hardening them off in a garage or shed for a few days to acclimate them to the temperature change.) Firmly tamp down the soil around the edges of each pot, leaving just the top lip exposed. Water plants thoroughly, and water the soil around them as well for extra help cozying them in.
Step 5: Luckily for those of us with no patience to wait for spring, cold frames can be adjusted to different climates. In colder areas, you can bury the edges of the cold frame in hay, chopped leaves, soil, or sand for greater insulation, and lay blankets on top for the coldest nights. In mild climates, you can vent the windows during the day and plant a wider array of less sensitive herbs.
Step 6: Prop open the windows for ventilation on sunny days—too much heat can kill plants much faster than frost. After outside temperatures reach 40 degrees, you'll want to vent them, and lift them up entirely if temperatures rise above 50. (Don't forget to close them back in at night.)
No cold frame to speak of? Shop our picks for 10 Easy Pieces: Cold Frames and 5 Favorites: Cold Frames to Warm Up the Garden.