For a warm cold frame you need fresh manure or leaves as a heat source.
With fresh foliage, that must not be too wet, However, only moderate floor heat is achieved. The height of the foliage pack must 25 be up to 30cm. Good and even heat development is achieved with fresh manure (horse manure is best) and foliage. First the manure is layered (20 to 25 cm) and put a layer of leaves about 10 cm thick on top. Then the windows are put on immediately. Only when the pack has warmed up well, the earth is raised, best good compost soil in a layer of 10 bis15 cm. The outside of the packed cold frame should also be covered with manure- or foliage layer are protected.
Depending on the weather, the cold frames are packed from mid-February.