Building a cold frame or greenhouse bed in your backyard will allow you to have instant access to fresh vegetables in both the early spring and late fall. The methods to building a simple and low cost season extension garden bed have been adapted from Niki Jabbour’s book: A Year Round Gardener.
In late fall, far past the first fall frost, lots of annual greens, veggies, and herbs such as arugula, beets, carrots, parsley, tat soi, mizuna, kale, swiss chard, dill, spinach and rosemary can be harvested - up until the first days of winter!
Soil will also be ready for planting very early in the spring if you leave the plastic on over the winter (and shovel off the snow - which is lots of work) or a little later if you remove the plastic and replace it when the snow has melted. Greens will be available to eat in early to mid-May, but be sure the soil is warm before planting or your seeds will rot. Kale, lettuce, arugula, and tat soi will be ready-to-eat in mid-May with seedlings of root veggies, swiss chard, and herbs already sprouted for early summer harvests.
Step 1: Build a raised bed of your choice. Many online resources and books will help you do this. This does not have to be complicated but make sure you account for good drainage or your bed will be pushed apart by frost heave. Dig a trench around all sides your bed and fill with gravel. Place the bed on top of this trench.
Step 2: Purchase flexible PVC pipe in the plumbing section of your local hardware store in two sizes. We used ½” (inch) pipe to create the frame and ¾” (inch) pipe to secure the frame to the raised bed.
Step 3: Slide the ½” pipe into the ¾" pipe and secure it to the bed using a plastic clasp (also found in the plumbing section). The length of the ½” pipe will depend on how wide your bed is and how high or low you want your frame to be. A shorter pipe will create a lower frame.
Step 4: If your frame is small and you will remove the plastic over the winter you will not need a ridge. Otherwise, create a center ridge to hold up the hoops of the frame in winter.
Step 5: Attach plastic sheeting; we used 6 mil polyethylene sheeting that was left over from the building project. Create a weight using two pieces of wood. Roll one piece in the plastic and nail or screw another piece to it. This provides some weight to prevent the plastic from blowing around and tearing.
Step 6: Attach one weighted end to the raised bed and leaving the other free. This way you can open the bed part way (at 4 – 10 degrees Celsius) or completely (above 10 degree Celsius).
Step 7: Use the ¾” pipe to create a clasp by cutting a small portion out.
Cut off the four corners so it is easier to slide on
Step 8: Use the clasps to secure the plastic to the frame. Otherwise it will blow off and tear on windy days.
Step 9: Enjoy fresh food while the snow flies!