Posted: 19/01/2013 at 15:56
I have a 2.2m x 4.4m green house and I would recommend pouring a single concrete base exactly the same size as your green house so you don't get a ledge whihc can let in damp through standing water, expecially important as you are going for wooden frame.It is a fair bit of work but it is easy enough to do, dig out at least 20cm and fill with hard core. Get your wooden frame set up to pour a base at least 15cm deep. Hire a cement mixer, get a couple of big strong mates round, and mix and pour the concrete base.
Open soil nees replacing, you will get diseases, damp and fungal problems which are hard to eradicate. A concrete based GH is easy to keep clean and didiease free. Use big Square pots so you maximise space.