I made a vegetable planter out of pallet wood. I used heavy pallet boards to make the legs and for the bottom to hold the weight of soil.
When I built the sides, I left enough room at the bottom (above the brace), so I could slide boards in and out, just in case one needed to be replaced. For extra bracing underneath, I added a couple of thicker boards and used Simpson strong ties to attach them. I used ties as well for added support in the bottom corners.
I also made a divider out of plywood to slide in the middle so we'd have to separate compartments. We are going to line it with landscape fabric and then add the soil.