A cold frame will get your seedlings off to a flying start in spring. Cold frames don’t have to be complicated structures or require carpentry expertise. We make ours from some old bricks and windows, and a small quantity of watered-down white or cream house paint. Materials for this type of cold frame can be found at the local tip or building recycling centre. If you don’t have any left over paint, a small sample pot from the hardware store will provide enough paint for this job. Dilute the paint until it provides a slightly opaque coating to the glass. Some hessian bags, an old blanket, or a large piece of shade cloth or weed mat can be used as a cover at night to prevent warmth escaping.
The size of the cold frame is determined by the size of the window. If we only have a small quantity of seedlings that require warmth, we build it to suit one window frame. Three layers of bricks provide ample room for most seedlings. The cold frame will have to be set up in a warm spot to be effective. Close to a north-facing wall is best. The bricks in the cold frame will absorb and store heat during the day and release it slowly at night, keeping the seeds and seedlings warm. However, the cold frame can lose warmth through the glass at night, if it is not covered. Place hessian bags a folded blanket, or crumple shade cloth or weed mat on the glass panels in the late afternoon, and remove them mid morning when air is warmer.
Once seeds have germinated, prop the front of the lid open slightly with a half brick or something similar during the day to allow adequate ventilation.
This type of cold frame is easy to construct and to dismantle when the weather warms. The bricks and window panels can be stacked behind a shed or in an unobtrusive corner.
