Hi, I hope you might be able to help. I'm about to enter my second year of growing vegetables. We have a small garden and last year only a very small space for the patch. However, we have a large patio and I wondered whether it would be possible to buy some railway sleepers and fill the space with soil, on top of the material you line ponds with. Is it possible to build a raised bed on top of a patio with railway sleepers forming the outside? If so, could you suggest what sort of depth I need to be looking at? If I do go down this route, is there any other advice you could give? Thanks.