Adding a few weeks on to either end of the growing season can increase the yield of your vegetable garden and allow northern gardeners to experiment with longer-season varieties. In the coldest climates, gardeners can take advantage of season-stretching techniques, setting plants out earlier and harvesting long past the first frost. Combine cold-hardy vegetables like broccoli and cauliflower with frost-protected tomatoes and eggplants for the longest---and most productive---growing season possible.
Use water-filled rings. Available in garden supply stores and catalogs, these cone-shaped, water filled tepees surrounds a single plant. As the water inside the tepee freezes, it releases heat and protects the plant. These are used early in the growing season to protect small, immature plants.
Cover vulnerable veggies. Floating row covers are lightweight fabric sheets that protect from frost and wind. According to Colorado State University Extension, they provide 2 to 4 degrees of additional frost protection.
Create a heat tunnel. Install hoops at 3 to 5 foot intervals in the garden bed, and protect several plants at once. Fasten plastic sheeting to the hoops. This is similar in protection to the floating row covers (2 to 4 degrees of additional frost protection) and must be removed when temperatures rise.
Build a cold frame. Cold frames are very primitive greenhouses, and they can house and warm plants throughout the colder growing months.
A simple cold frame can be made from four to six hay bales. Arrange the bales in a square or rectangle in a sunny, flat area. Add several layers of newspaper to the bottom and add your plants. Cover the frame with clear plastic, an old window or a large plastic sheet. Open the cover every day to prevent overheating.
According to Colorado State University Extension, a cold frame can add 3 to 6 degrees of frost protection and two to six weeks on either end of the growing season. Covering the frame with an aluminum "space blanket" and adding a strand of C-7 medium-sized Christmas lights increased the frost protection 30 degrees.