Who says you can’t have lettuce in December? Just because the weather is beginning to turn colder doesn’t mean it’s time to stop gardening. Gardeners with a greenhouse simply move their growing operations indoors for the season. Even if you don’t have the money or space for a greenhouse, it’s still possible to extend your growing season for a bit longer.
Think of a cold frame as a mini-greenhouse for the garden. It’s a bottomless box typically made from rot resistant wood or concrete blocks that are often insulated. A sheet of glass or similar glazed surface that prevents heat from escaping gets positioned over the top. Cold frames are slanted to face south to take advantage of the winter sunlight. Often, the inside is painted white on the inside to help diffuse the light. You can build one yourself fairly easily or purchase one either online or at your local garden shop or nursery. While some cold frames are made of wood, others consist of an aluminum frame with glass or clear plastic over the top and sides. Choose a model that will last several seasons and hold up to the elements throughout the winter. If you live in an area that experiences consistently bad weather all season, consider spending a bit more money for a heavy duty model.
In wet areas, you can place gravel inside the box to improve drainage. Additionally, to extend the growing season through the winter months, place dark colored rocks or water filled jugs painted black throughout the box. They will heat up during the day and then release the heat at night to prevent the plants from cold related damage. This same principle is used in large scale greenhouses that employ thermal ponds for the winter.
The cold frame keeps warm air inside the box, which in turn heats the soil the plants are grown in. This encourages plant growth. Just like a greenhouse, you’ll want to let air in as well. You’ll want to lift the glass top and prop it up to encourage air flow. If you’re building the cold frame yourself, be sure to hinge the frame that holds the glass for easy movement.
Cloches are frames made of plastic that cover the plants and maintain warmer temperatures to encourage growth. You can typically make one using PVC pipe, clear plastic, and some rope. With it, you can make a tunnel cloche to protect a large bed of plants. Additionally, many garden centers and nurseries carry small plastic cloches for individual plants. Venting is key, so make sure there is a way to vent the cloche to let air in and regulate the temperature.
Initially, you may wish to start small with the individual cloches until you get the hang of the garden process. The good news is that you can hang on to the individual cloches even after you’ve built a bigger one. They come in handy to protect sensitive plants from the effects of sudden cold weather.
Tips for Out-of-Season Growing Success
Since you’re growing in a smaller space, use it efficiently. A productive garden begins with healthy soil, so be sure to add amendments and compost to the soil before you begin planting. Keep in mind that your plants may be hungrier in the winter as growing outside of their regular season may be stressful for them.
When watering your plants, plan to do so during the day, preferably in the morning. You may consider warming the water slightly before watering your plants with it so the cold doesn’t shock them. Watering in the morning means it’ll have all day to warm up and warm the soil in the frame.
Also, keep in mind that ventilation is essential to release some of the built up heat on sunny days. Try to ventilate slowly to ensure the cold air doesn’t negatively impact your plants.
Plants that grow well in cold frames and cloches
Many plants grow well in cold frames and cloches. Cool season crops tend to do best since they’re not as easily shocked by cooler temperatures. These plants include Swiss chard, kale, spinach, parsley, and many lettuce varieties. Additionally, carrots, radishes, and parsnips may also grow well. These greens and root crops are yummy in salads and even work for a hearty winter stir fry.
As with any garden, carefully think about what you will actually eat. Since space is at a premium, don’t waste time on vegetables you and your family don’t really like and won’t eat, even if it is neat to grow food out of season. If you’re a huge fan of salads, by all means, grow all the lettuce you could ever imagine in your cold frame or cloche. Be sure to stagger seed sowing so you can enjoy the greens all, or nearly all, winter long. If you’re feeling adventurous, try different varieties of your favorite cool season vegetables to enjoy the diversity of flavors. Whatever you plant, be sure to check in every day, sometimes several times a day, to assess the health of the plants, release hot air and water if necessary.