Posted: 08/04/2013 at 09:54
Using the sun is the best way but no use during winter. Having the greenhouse in full sun and dug about 1 metre into the ground surrounded by stone chippings, having the floor tiled all retain heat and use the earths heat. A thermostatic fan heater will then keep the heat around the greenhouse.
Blairs, could you give a little more info 'dug about 1m into the ground surrounded by stone chippings'. At the moment I'm visulising a sunken greenhouse! Can't think thats what you mean. Only ask as I am getting a greenhouse this year and am trying to gather as much info as pos so I get the right base laid. Thanks.
Until recently all greenhouses were built into the ground - at least 1 metre with a trench around them. You only really had a top few feet of glass. Frost only penetrates the top 3 inches and the earth naturally keeps plants above freezing point. If you put stone chippings around the greenhouse (they were built with brick foundations) then that is a heat sink as the stones retain heat. You could make the greenhouse warmer by using hot beds - grass clippings as blackest has said. It takes a bit of work though!
The bog standard glass greenhouses loose heat as it escapes out very easily. Have a brick foundation and it looses less heat and the brick retains heat. I would also always have a stone/paved floor in a greenhouse. Earth is no use.