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How to build a raised bed on a concrete base



welcome to GoY.
firstly you have to decide what you want the raised bed to be made from. brick or timber.
if you are using brick then make sure the bricks are keyed onto the concrete securely. leave drainage gaps at the base or it will fill up and become a bog garden.
if timber then use tanalised timber as it will take a lot longer to degrade. the wood needs to be secured with screws. Stainless steel will last longer.
once built to the height you want finish it off with what ever edging you fancy.
Then I'd put a membrane in to keep the soil off the timber/brick and then fill with the soil you need for the plants you want to grow.

25 Jan, 2017


I agree with Seaburngirl :o) I would put some rubble in on top of the membrane for drainage too :o))

25 Jan, 2017


Will certainly need good drainage, is there any way you can drill several large holes through the concrete? Bricks will enable you to leave drainage gaps but not sure how this would work with wood.

25 Jan, 2017


Honestly, I would take a sledge hammer to the concrete. Break it up, haul it out. You can build a simple frame with scrap lumber and "L" brackets - any size or shape to accommodate your space.

Advantages of removing the concrete: better drainage as Mg stated; root vegetables - parsnips, carrots, beets, leeks, etc won't be restricted, most need at least 2 feet depth for proper development; more hospitable for earthworms, the tillers of the earth, they traverse to a depth of 6 feet bringing essential nutrients to the plant's roots.

Finally, certain chemical agents are added to concrete which are known carcinogens - aluminum powder, insoluble esters of carbonic and boric acid, silicones, Sulfonated melamine formaldehyde condensates & others. You'll have to research leaching chemicals.

25 Jan, 2017


Yup Bathgate is correct!

25 Jan, 2017

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