Full question:
We are about to build our first green house using recycled windows. Is it best to sit the house on a solid surface i.e. concrete or paving? I understand this will give thermal mass making the house warmer. A solid surface will also make it easier to sweep out and keep clean.
Or is it better to site it on a dirt floor and therefore be able to grow some plants directly in the soil to get the benefit of the soil bacteria. Is growing in very large pots as beneficial as growing in the ground?
The house will be fairly small 3m x 2m.

Our response:
Growing in the ground will always be better than in pots. A solid floor may warm up more quickly but it can also cool off quicker than soil.
You could consider a concrete strip in the centre as a walkway which will help make the house warmer. 🙂