Let’s face it – out of season greens just don’t have as much flavor as the ones that come fresh out of your organic vegetable garden. What if there was a way, though, to keep growing lettuces and herbs at least until you have your family over for Thanksgiving or Christmas without having to invest in constructing a greenhouse? Turns out that prolonging your growing season can actually have a simple solution in the form of cold frames. Cold frames are low, protective structures that cover your plants once the climate starts to cool. The best part about cold frames is that not only are they easy to make yourself, but they also can be as permanent or temporary as you want them to be.
What you’ll need
Cold frames can be inexpensive to make because many of the materials can easily be repurposed and don’t have to be bought new. Here’s what you’ll need to get started with being the latest talk among your urban gardening friends.
The first thing that you’ll want to acquire is a good cover. This can be either glass, polyethylene or fiberglass. A flexible piece of greenhouse covering will even work. Old house windows can be wonderfully repurposed as a cold frame cover. Look for one that is three to four feet wide and doesn’t have any health hazards such as lead paint on the frame. You’ll also want to check to make sure the frame isn’t rotting and that the glass is firmly secured so that your cold frame will keep frost out and won’t fall apart halfway through the winter.
Your region’s winter climate may play a large role in the type of material your cover is made from. Areas that experience heavy snowfall may want to opt for a material that is more durable than regular glass.
The frame can be made with materials as simple as bales of hale to as sturdy as rot-resistant lumber or cinder blocks. Most people, though, prefer to use wood. Cedar, cypress and redwood are naturally resistant to rotting and won’t need to be pressure-treated. You’ll want to avoid any wood that has been pressure-treated because the process involves the use of highly toxic substances such as arsenic – something you definitely don’t want to grow your rosemary in.
Using wood glue, attach the pieces of lumber together at the corners and then secure them with elbow braces and two 1- or 1 1/2-inch galvanized screws. Once you have the frame constructed, attach the window to the top using sturdy hinges. Instructables has great step-by-step instructions with photos on how to construct cold frames.
Before you place your cold frame, you’ll want to think about how you will insulate it. Some people dig a pit before placing it within the hole so that they are actually planting six to eight inches below the surface. This allows your plants to put down roots below the part of the ground that is typically frozen. If you don’t want to do something so permanent to your garden, you can put manure compost in the box as a natural source of heat. Don’t plant directly into the manure, though. Be sure to cover it with six to eight inches of soil. This will turn your cold frame into a hotbed! On days that reach 40 degrees Fahrenheit or warmer, you’ll want to make sure you prop open the cover so the heat can escape – otherwise you’ll cook up all your veggies!
Once you’ve constructed your cold frame and decided how you are going to keep your plants insulated, it’s time to place it in your yard. You can either set it in your vegetable garden or a new location. Ideally, you’ll want to try and make sure it is facing south for maximum sun exposure during the short days of winter. If you live in an area that experiences snow, you may not want to put the cold frame too far from the house, otherwise you’ll have to pull on your boots every time you need a few basil leaves. Don’t forget to brush off any snow that accumulates on top of the cover so that your plants continue getting enough sunlight.
Tips for gardening with cold frames
Now that you have your cold frame ready to go, or have at least gathered your materials, you may still be unsure of exactly what you can grow. Veggies that you would grow in the early spring are all great candidates, such as:
- Bok choy
Basically, you can grow almost your entire salad bowl year-round! Some herbs will also do very well in a cold-frame, especially if you insulate it with manure to create a hot bed. Once you’ve got your plants in place – it’s basically just like a regular garden. Enjoy!