I'd agree with Janet that #1 seems best. I would worry somewhat about the extra heat generated by the concrete surrounding the beds. Is it dark colored? I know there is a big difference in the moisture needs of pots sitting in grass and those on my concrete porch. 'Course it gets hotter here but Illinois gets pretty hot too, just for shorter periods. I'd add an extra 6" depth to your boxes just for cooler root run and to hold more moisture. josh

I put in raised beds this summer on top of my concrete backyard, about 18" tall. I pretty much just plopped the dirt into the enclosures, although as I came across rocks and sticks I did use those for a bottom layer, thinking of drainage and also just to get rid of them. I'd love to hear what you decided and how it works out.

I built a raised bed on concrete last spring. It's about 14" deep and just shy of 4 feet long and wide, bottomless and has a trellis nailed to one side. If I were doing it all over again I would make it 18" like newskye.

The concrete slab I built it on has a very slight angle so that helped with drainage. I also used a chunky, loose soil mix. I successfuly grew okra, beans, snap peas, and cucumbers in it (not all at the same time).

I have pretty hard, mostly decomposed granite soil in my back yard, which is covered by a porous synthetic weed shield and about 4 inches of 1/4' and finer decomposed granite. I want to use raised bed gardens so I don't have to dig up my landscaping, because breaking up the existing soil would be a real chore, and the soil quality is not good. What I wondering is will I be able to get away with a 1 foot bed or do I need to go 18"? Thanks!

Would love to know how/what worked out for everybody. I am putting 2 raised garden beds on my concrete in the backyard. I was directed to this site because I was wondering if I am just supposed to put the soil directly on the pavement in my bottomless raised bed.

I have been doing an internet search all day, and I came across a suggestion to put newspaper on the bottom before putting the soil down. Has anybody heard of this?

Otherwise, I will just put directly on concrete. Can't wait to get started.

You just need drainage at the bottom where the beds meet the concrete, the cardboard won't add anything. I left the bricks meet at the bottom un-mortared and threw dirt straight in.

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I will be putting raised beds on old concrete slab in the city and after much ruminating believe that a layer of stone (or recycled wine corks) at the bottom of the box is a great idea... not only for drainage but also for air flow and isolation from concrete... seems to make sense...

Let us know how it works for you!

It is almost like container gardening, putting beds on concrete. You might want to post in the container gardening forum for more specific advice.

I used cinderblocks on a concrete slab at a house we were renting - I just dumped the soil in the middle, then filled up the holes in the cinderblocks.It was marginally successful for herbs and more successful for succulents. If I were to do it again (we moved) I would use garden soil rather than a lighter soil...I think it would hold moisture better. At this house I am using smart pots for tomatoes...tomatoes are thriving.

it's past summer, but i'll add my 2 cents, may be for next year will come in handy. how about using cinderblocks or pavers with holes in them to allow for drainage - use them as a bottom layer to support the box. then fit inside window screen netting or perforated metal grid to retain the soil . and then put a layer of argi-cloth, permiable, for drainage. it'll prevent buggies from crowling in thru the bottom too. when soil is on concrete, doesn't it stain it? if you use pavers, the soil will remain cooler too and drainage is much easier.

Thank you it's really help !!!