With this new corner brace, I expect the end boards will last considerably longer than just bolted wood. Time will tell.
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.
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.