Hmmm. Good question. I don't have an answer, but you might also post this to Tips and Techniques or maybe Soil, Compost and Mulch. In those forums, you might also mention if it's intended for an accessible garden.

Good luck with it.

Great idea! Yes it will stain the concrete but you could start with a contractor's inexpensive polyvinyl tarp. Any hardware store or place like K-Mart has them. Check the sizes available and build the raised bed to use the tarp for concrete protection. If you place one edge of your bed on the low side edge of the concrete you can leave that edge of the tarp run out over the edge of the concrete to permit heavy rains to leach out of your garden. I might also suggest a fairly heavy use of peat moss in your bed for a lot of good reasons. It will hold water for you. It will make your growing medium easier to work. The plants will love it. I would use a whole large bale of it in a 4 X 10 raised garden.

You can remove all stains from concrete with a power washer and some cleaner. I have an inground pool with a cement surround and every year we have to power wash it due to leaves sticking to it and other debri, therefore staining it. It works well. you can rent a power washer or find some one who owns one and borrow it for about an hour ;)
good luck with all you do and have fun!!!!

Hugs
Maigan

To prevent weeds and mud, I have put down a large tarp over my dirt yard, can i make the raise garden over the tarp?

What would you use to remove the stains? We aren't gardening on our patio, but using a power washer did not remove the stains. I'd like to know of a good cleaner.

Nancy