These beds were made as an experimental prototype with 1×6 cedar boards. This makes them about 11.5 inches tall. They are held together and supported by 2×2 boards that were all cut with one straight cut and one 45º cut so that they could be driven into the ground for stability. They are going into their 6th Spring planting season so I have no regrets about the $17 investment I made in materials.
The surprise came when I started trying to fill them with soil. Now, I can look at them and visualize bags of soil piled inside and imagine how much it would take to completely fill them. I no longer think they need to be built so high. When first installed, they ended up being about half full. Now after seasons of freshening them up with compost and organic nutrients they are almost full and look great!
The next ones I build will be constructed of 2×6 rough cut cedar which is a very substantial and naturally long lasting piece of lumber. I’m going to use metal brackets in the corners to hold them together along with a couple of long screws directly in the boards.