If it makes you sad to watch your garden wither with the first hard frost, there is an easy and inexpensive solution: extend your growing season by building a cold frame. Cold frames are a low-tech solution that will let you keep growing for weeks (or months) longer than usual without the expense of a greenhouse.
What Is a Cold Frame?
A cold frame is a bottomless box with a transparent lid (usually plastic or glass) that sits directly on the soil. It captures sunlight and holds heat like a mini greenhouse. The passive solar heating, wind protection and insulation it provides will allow your plants to continue growing well into the colder months.
Cold frames are also great for giving your plants a head start in the early spring by protecting tender seedlings from cooler temperatures and the potential for frost. They can help you harden off seedlings because you can simply raise the lid for progressively longer periods until the plants are ready to face nature without the protection of the cold frame. This is more convenient than having to move plants inside and back out every day until they are ready.
Easy Cold Frame Construction Methods
A cold frame doesn’t have to be anything fancy, and you probably have the materials to build one sitting around in your garage. Here are some easy ideas for creating your cold frames this year.
- Straw bale frame: stack bales of straw around your chosen garden bed and top with an old window. This is probably the cheapest option and no tools are required.
- Recycled window frame: build a simple wooden box that will support an old window or shower door as a lid.
- Cinder block frame: stack cinder blocks for sturdy weather-proof walls and top it with a clear lid.
- Hinged wood box: a more polished version with a sloped, hinged lid for easy ventilation control.
No matter the construction method you use, there are some important features that you want to pay attention to.
- Create a slope so the lid faces the sun.
- Make sure that the lid can be propped open to control ventilation.
- Locate your cold frame in a sun-facing spot.
Best Plants for Cold Frame Growing
If you want to continue growing fresh food into the winter, a cold frame can provide a great environment for these crops:
- Leafy greens like spinach, lettuce, kale, and arugula.
- Root vegetables such as carrots, beets, and radishes.
- Young brassicas like cabbage and broccoli starts.
- Herbs, including parsley, cilantro, and chives.
In the spring, use your cold frames to harden off tomatoes, peppers, and other seedlings before transplanting them into their permanent summer growing spot.
Seasonal Tips for Cold Frame Success
Since cold frames are a low tech tool, there are some things you will want to pay attention to in order to keep your plants healthy. On warm sunny days, be sure to open the lid a bit to prevent overheating and burning your plants. Since rain can’t reach inside, water your plants carefully. Make sure the lid is closed tightly on frosty nights. Now is a great time to build your cold frames for fall and winter growing. You want your plants to be established before the coldest weather sets in.
You don’t need big hoop houses or a fancy greenhouse to grow your own food well into the winter months. A cold frame is one of the most cost-effective tools for stretching the growing season. By relying on passive solar heating, a simple frame offers frost protection, shields tender plants from harsh winter winds, and creates a warmer microclimate that lets hardy crops thrive even when snow is on the ground.
