The inside of the cold frame was painted black. This increases the heat energy absorbed from the sunligth coming through the window. The seedling trays and the soil in them are also black. If we used any other heat source besides the sun, it would be a 'hot frame'.
Portable Cold Frame This cold frame is made in three stackable layers to make it portable. It can hold nine trays of seedlings, and includes a watering system that can be operated by a timer.
