An unheated greenhouse is used solely to keep a killing frost off plants. In the spring, it may be used to start seedling and to help you get a jump on gardening. In fall, it can extend the gardening season well past the first frost. However, in winter the unheated garden is primarily used to keep frost away from hearty and woody plants. In extreme northern climates where the temperatures turn bitterly cold, gardeners who use a cold greenhouse must take steps to protect their unheated plants from hard, bitter freezing temperatures.
Wait until plants enter their dormancy period. Plants typically go dormant after long-periods of darkness.
Cluster plant containers together and water one last time with a garden hose before you overwinter them. Moist potting media is slower to freeze, and will offer more protection to the roots of the plant.
Drive garden stakes into the ground surrounding the containers with a rubber mallet.
Cut chicken wire so that it will wrap around the garden stakes and form a cage around the plants. The chicken wire cage should be open at the top, but the walls should be taller than the plants.
Nail the wire to the stakes using fencing staples and a hammer.
Fill the chicken wire cage with dead leaves. The leaves will insulate the plants from the cold and help them survive the winter. Ensure that the leaves completely cover the plants, and that no branch tips stick out.