From what I understand Blast cedar isn't treated because of it's natural resistance to rot.

In fact, I pulled up my old beds (treated pine fence boards - trying to do it on the cheap) when I realized the leaching problem, and am planning to rebuild them with cedar boards.

I built mine 3'x 6' by just driving stakes at the corners and securing the boards to the stakes. The 3' width was manageable (I could reach in from either side easily to weed / harvest my goodies).