Bonsai Coldframes

It is easy to construct a simple coldframe for bonsai. Before the ground is frozen, dig a hole at least 1-1/2 feet in the soil. Make the hole as long and as wide as you need for all your plants. Line the sides of this hole with exterior grade plywood which extends 6 inches above the surface. Put 4 to 6 inches of gravel in the bottom of the hole, set your plant containers on this gravel, and spread straw around and over them. Put a loose-fitting cover on the frame made of polyethylene sheeting or any similar material.

Be sure the top of your coldframe is strong enough to withstand a heavy load of snow. Ventilate on days when the air temperature is above 40 F degrees to keep the plants cool and dormant.

To purchase a coldframe kit, check your local nurseries or see catalogs of mail-order garden supply houses.