Built a raised bed out of 2x6s from the ReStore and watched it bow out by August
When I put in my first raised bed behind the garage on Oakley Street back in 2019, I used 2x6 cedar boards screwed straight into the corners. By August the sides were bowing out like a boat, and my neighbor Doug pointed at it and said, "You forgot the brace in the middle, didn't you." Ten dollar fix with a scrap 4x4, and it has held straight for five seasons now. So what is everyone using to brace long beds, or do you just go with 4 foot sections and skip the problem?
I read on a garden forum that the general rule is a brace every 4 feet for beds over 8 feet long. The 4x4 trick works, but a lot of folks just sink a piece of rebar or a metal L bracket on the inside of the board instead. I did the 4x4 method on my 12 foot bed and it stayed put, though it does take up a little soil space.