Proserpina's Patch

All my GHs are on slabs or concrete from choice.  I have beds on 3 sides and there's plenty of room to grow stuff without worrying about roots and pests coming up in the soil from outside.
The compost in the beds in GH1 has been there for about 40 years. It has a top up every year when I empty the tomato pots on it but I've never had to remove any soil.

Do you mean you have beds on top of the slabs, Veggie? That's sort of what I was visualising for mine, but I wasn't sure if it would work. I suppose it's not really any different to having a big container on top of the slabs.