raised beds

[cme4dk]

I have been asked to oversee construction of raised beds for a community garden, the proceeds will go to a food bank. The site is over a concrete slab and I wanted to make the raised beds about three feet by nine feet, about 2 feet high out of cedar. To keep the costs down, would 3/4 inch planks work?

[daddo]

If you can get 12' boards, you can make the bed 9'x3' and make just one cut and eliminate splicing and any waste.

What is planned to enforce the sides? 3/4 I think would be fine with proper support.

Plastic against the side boards would help keep the side boards from being wet all the time.

A small gap at the bottom could allow drainage.

[JerGar]

Maybe add a vertical cleat and cross piece every 3' or at least halfway on the inside.

[R Clark]

I made three raised beds out western red cedar this year for our garden. I used 2X8X12 dimensional lumber. 6X3 boxes and about 22" tall at finished height. I didn't do a whole lot of research when I started. Regular 3/4" planks just didn't seem beefy enough for what I wanted. Yeah, it was pricey, but I'm only doing it once.

That size bed is going to take a lot of soil to fill. Nominally nearly 3 yards each. Mine went straight on the ground and so I don't worry about drainage. You may need to take that into consideration since yours will be on a slab.

[Steve N]

cme4dk said:

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The site is over a concrete slab and I wanted to make the raised beds about three feet by nine feet, about 2 feet high out of cedar.

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Cedar works great as a deck, or fence wood, but in constant ground contact not so well. Pressure treated pine would last much longer, just throwing that out there.

You say 3x9. I agree with 3" width, anyone can sit on one edge, and work to the middle of the box. 9" long is just crazy money though. I can't see where you would get that much more planting in that 1', but going over 8' long (standard length for most all wood you will see used outdoors) is going to just about double your wood budget.

Home depot, probably Lowes too has 4x4. and 5x5 Cedar beams x 8' long. Laminating this up is obviously doable. but for an outdoor structure filled with dirt I have to wonder why you would bother.

"On concrete" this will cause more problems than not. What is your plan to fix these to the ground? Rain and the resulting flow through your dirt will have spil leaching out from under these year round.

The last is 24" tall. I am assuming you are putting in seasonal garden plants. veges, herbs, etc. 8" would be more than adequate. again total material cost is the difference. Possibly you could explain what 24" would be needed for?

You will want to overlap your ends as shown here.





I can attest these will work as well as anything you might find for securing your ends together




Straight forward project here, don't overthink it.


I suppose your thinner boards on edge might be able to contain the dirt, but with the wider beams you also provide a seat for someone working the bed to sit. Having done it both ways the seat always gets high marks from users.

[K. L. McReynolds]

Concrete block. Three high with 1" thick pavers as caps. Make drain holes between the bottom blocks.

Those will out last wood and almost anything else.

[cme4dk]

I planned on using 2 X 12'S. So 2 of them will be just under 24 inches. If I get the 12 foot length one cut will give me a 9 foot side and a 3 foot side.
I have since called my local lumber yard and they only carry 2 X 6's so I can make it under 18 inches high using three boards stacked.

[chips ahoy]

I built mine out of rough hemlock. 2"x8"x10'. Won't rot but sure is heavy. Built them 16" high and been used for three years and showing no wear.



Mel

[FS7]

cme4dk said:

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I have been asked to oversee construction of raised beds for a community garden, the proceeds will go to a food bank. The site is over a concrete slab and I wanted to make the raised beds about three feet by nine feet, about 2 feet high out of cedar. To keep the costs down, would 3/4 inch planks work?

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Man, I overengineer everything, but not as bad as suggested.

I've done many planters out of cedar and I use 3/4 for everything. The biggest was about 6' x 2' and it's fine. The legs are all 1x material as well and they hold up fine. You can get away with vertical legs every 24" or so. It doesn't have to be complicated.

At that size I'd probably do a "main" leg at 54" with extras every 18". This gets you a lot of extra support. Cedar is actually fairly strong in this regard, though it's light as a feather. Just don't move it with soil in it.

For smaller boxes, you can put a few cross braces in (every foot or so). I pocket screw mine internally using deck screws so they don't show. Above that, use fiberglass screening and landscape fabric to hold the soil in. It'll drain well and it won't rip. You don't need screening on smaller boxes, but on one that size I'd do it. Staple the mesh to the sides and trim the top. You might also consider adding a brace on the top as well as the soil may very well want to push the sides out.

[sroxberg]

Here is a picture of the ones I made. 32" tall and 4' x 8'. bottom is covered with wire and then landscape fabric.

You can put overhead sprinklers in if you desire as well.