If you have a local lumber mill, go for locust. It's a tough wood that's
been used many years for fence posts and has a proven track record. I had my
boards cut to 8-inch width. My beds are deep enough to grow very good and
long root crops (carrots and parsnips) in those beds. There are a couple of
boards that have warped a llittle, but it's only cosmetic. I've had my beds
in place for five years now and they look good. Life expectancy for the
locust boards is probably 25 or 30 years. . . I hope I live to see them rot.