I have been using raised beds for several years now. I converted an existing patch of grass into four, 4ft x 12ft raised beds for a total garden area of 192 sq. ft. This could, conceivably, produce enough food throughout the year to make a serious dent in the food budget. And, of course, all the advantages of raised-bed gardening are realized. However, I have had to replace several end boards due to rotting out at the corners. In order to prevent this from happening, I came up with a way to use concrete as a corner brace, and thereby stop the rotting and make a more permanent installation. Starting in step 7, I show how to replace an end board that has rotted out at the corners.
Step 1: Materials Needed
The usual concrete tools, materials and supplies. For my mix, I used a ready mix concrete so that I would be sure to have a uniform, strong concrete. For the bed itself, I choose to use 2x dimensional lumber. At least one bed is made with 2x12's, one with 2x10s, and so on. A 2x6 is certainly big enough, so it is a matter of personal preference. In this instructable, the lumber is 2x8's.
Step 2: Making the Form
The form is made using 1/4in. plywood, and 1x6 lumber cut to the correct sizes. See pictures for specifics. A key part of making these braces is the addition of a piece of wire mesh into the mold. I chose to use some rabbit wire for my reinforcement. It is easily cut with wire cutters, and shaped to fit within the mold between the bolt holders....these have been made out of regular PVC pipe, which is the 1//2 inch size. The form is assembled using drywall screws. Before assembly, it is a good idea to apply a coat of oil to the wood pieces to act as a release agent for the concrete. I just used some vegetable oils, but any oil will do.
Step 3: Mix and Pour Concrete Into Form
Plan on letting the form set for 24-48 hrs to insure maximum strength. Concrete goes on curing for several more days if not weeks, but 48 hrs is sufficient for the first set.
Step 4: Remove Brace From Form
I unscrew the outside piece of the form which moves away easily after the bolts have been removed. By gently tapping on the wood part of the form, the concrete easily separates. So what we have is a corner brace of reinforced concrete, "predrilled", ready to accept your end or side pieces, and should last a very long time. Will simplify any future replacements should they be necessary.
Step 5: Assemble the Bed.
To assemble the bed, I use 5/16in. Bolts of the appropriate length. For this particular bed, 4 or 4 and 1/2 in. bolts are used. One washer is used on each end of the bolts. For this example, the bed is 4ft on each side. Any size can be made, but my original beds are 4ft x 12ft. Make them the size that fits your space.
Step 6: Fill Bed With Garden Soil of Your Choice
In order to supply your plants with the absolute best growing conditions, you want to use a high quality garden soil. I have a compost bin, and also purchase commercial organic compost as needed to resupply the beds. Many books and methods are available for enhancing the gardening experience, and the viewer is referred to them for help in maximizing food production with this method of gardening.
Step 7: Replacing a Rotted End Piece
I have replaced several of these pieces, but they continuted to rot out. Hence the corner brace of concrete. Replacing the piece is simply a matter of unbolting the old piece, cleaning up the area so that the new pieces can be put into place, and installing the new corner braces.
Step 8: The Finished Repair Job.
With this new corner brace, I expect the end boards will last considerably longer than just bolted wood. Time will tell.