Made from untreated cedar 2x12s, with 4x4 posts in the corners. It cost me a fair amount of cash for both the wood and the fill, and I have two more boxes I need to replace over the next few seasons (you can see an old one to the left, with the electrical conduit trellis).
So my question to the good folks here is if I over-engineered or perhaps didn't account for something.
The 4x4 posts extend about 8" below ground for stability, as opposed to just resting the box on the surface like my previous ones. I'm not far enough down to be below the frost line in my area (live in the North, 2-4' is commonly how deep it can go), but it's also not attached to my house or is my house, so a little heaving shouldn't be the end of the world, right?
I put it together using #9-3.5" deck screws and attached each of the boards to the 4x4s, 3 screws per board, mostly because those were the biggest deck screws I could find at the hardware store at the time. Is that enough screws to hold back what is about 2.5 cu yds of fill comprised of compost, peat, and black dirt? The box hasn't seemed to bow at all, even after it rained the next day, so I don't think it's too much weight to bear...
Anyway, as I said, this wasn't a cheap project so I want to make sure that this is the right design for the next two before I hand over another $500 for lumber and $500 for fill and materials.