Author Options:

Raised Garden Beds out of Concrete Blocks? Answered

I want to build raised garden beds with the walls being made out of concrete cinder blocks. Want the beds to be about 2 1/2' above ground and about 3' to 4' wide. I also want to make basically concrete counter tops to put on top (or benches). My question is .. how many inches can the top go beyond the concrete cinder block frame without having to add braces for the bench? Ex: if I use 6" wide cinder blocks .. and fill the holes with rebar and concrete .. what is the overhang I can have on the bench top?


If you're going to mortar the thing together, then 4 or 5 inches easily. Assuming a ~2 inch thick benchtop, that is. The really critical element is the thickness of the bench top. Thin stuff (1 inch thick patio stones for instance) will fail pretty easily beyond 2 or 3 inches. If you're making the bench top yourself from raw materials, embed a metal screen (as in 1/8" thick wire screen,. not insect screening) into it for added strength.

If the overhang is 5" then the counter balance is only 1". Someone sitting or leaning on the edge could easily overturn it. Mortar cannot be depended to keep it stable. It will have to be anchored to the wall below.

? I must have missed it, but who said the bench has to be 12" wide? I was more worried about the durability of the bench.

I thought the question was "how far can the bench go beyond the blocks" as in overhang. Unless I read it wrong, which is entirely possible!

Exactly right, but you said "then the counterbalance is 1".. Anchoring is a good idea, and I would expect any bench/counter (rather than a simple capstone) to be anchored. instead of just flush mortared, as I thought she was aware from the comment about rebar.... Anchors would be embedded when the top stone is cast., Hence my focus on the thickness of the capstone, since the thickness (and embedded re-enforcement) in large part determines how well it will withstand shearing. But unless I missing something (and would enjoy being informed if otherwise) the counterbalance isn't just the single side overhang vs the wall thickness. I was under the impression it also was based on opposing overhand, total stone weight, and expected moment force. I would also suggest that if it will be a bench, the wall should leave off one tier of cinder blocks where the bench will go, since 30" is a bit high for a comfortable bench

I was saying that if the block is 6" and the overhang is 5" then that's only 1" of concrete balancing the bench. The inside edge would be flush or you're covering up the planting area. Good idea about lowering it, the top should be about 18 to 24 inches off the ground. Anyway just hope it doesn't fall off on anyone.

'Ah... I was thinking that she'd just have a larger counter, but I see your point.

'Anyway just hope it doesn't fall off on anyone.