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Using Retaining Wall for Raised Bed Without Drain Stone Behind Wall

westes Zone 9b California SF Bay

3 years ago

When building a retaining wall, the normal build practice is to use 3/4 inch drain rock behind the wall, in order to facilitate drainage down the hill that you are holding back with the wall. If you want to use a retaining wall just as a decoration on a raised bed that is two feet by 30 feet long, can you just skip this drainage rock? In a raised bed application, you do not have water descending in huge volumes down a hillside. Any water going into the raised bed should be draining straight down to the earth below. I would be using something like this Pavestone retaining wall kit.

Featured Answer

3onthetree

3 years ago

A raised bed would be defined as a "garden wall," not a "retaining wall" (then would require a base, design for surcharge, water drainage, etc). A garden wall only being a couple courses high if choosing some materials don't even need to interlock, be glued, pinned, etc. Your style of blocks you're using though, you should line the inside of the wall with poly plastic to prevent the seepage through joints and eliminate the "dirtiness" on the outside face.

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Comments (7)

Seabornman
3 years ago
You're not likely to get much pressure on a wall that height, and as you are not in an area that freezes, I'd say you'll be fine without drainage. You may get weeping of excess water between the blocks. I assume the soil inside is relatively well-draining.
westes Zone 9b California SF Bay thanked Seabornman
Seabornman
3 years ago
You're not likely to get much pressure on a wall that height, and as you are not in an area that freezes, I'd say you'll be fine without drainage. You may get weeping of excess water between the blocks. I assume the soil inside is relatively well-draining.
westes Zone 9b California SF Bay thanked Seabornman
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jrb451
3 years ago
You should be OK. So, you’re encircling a raised bed with stone and not building a retaining wall?
westes Zone 9b California SF Bay thanked jrb451
westes Zone 9b California SF Bay
Original Author
3 years ago
@3onthetree Do these kinds of walls tend to leak a lot? I would just document that a raised bed normally connects soil in the bed to earth, so any protective cover would be for the front wall only and would not cover the earth below.
3onthetree
3 years ago
last modified: 3 years ago
Yes, the plastic just on the side of the wall, the dirt should keep it held against it.

Leakage: The block's tapered shape (parallelogram) in a straight install allows the backfill to be right up against the face between blocks, so you will get some runoff with organic soil without the plastic. On retaining walls you won't see it because there's a wedge of gravel backfill right behind the wall.
westes Zone 9b California SF Bay thanked 3onthetree
PRO
Redwood Lawn & Landscape
2 years ago
Hi! I'm a landscape company owner in Georgia. We've found that while you do not necessarily need the drainage aggregate behind a small garden wall like this, it does not add very much cost to the project, so you might as well go ahead and put at least 4-6 inches of gravel backfill. This protect the wall and help prevent any dirt from flowing through the cracks in the wall, causing a dirty appearance. If you'd like to think about wall options a little more, check out our retaining wall page on our website.

Happy wall building!
westes Zone 9b California SF Bay thanked Redwood Lawn & Landscape

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