I had some cedar beds that must have lasted about 15 years. They were 1 x 6, stained x 2, and lined on the inside with black plastic.
I had hemlock beds that were not treated, got about 8 years out of them.
So, it will be interesting to see what the oak and hemlock does this time around, with the extra treatment of scorching + stain. I may also line the inside with plastic. Couldn't hurt, yes???
@wyoDreamer, I have good garden soil, so will only make them 6" high. I really don't need to do raised beds, could continue gardening in my usual fashion. But, I'm changing it up with the raised beds to FORCE myself to become more organized in my gardening plan. Instead of scrunching everything together, I hope that the beds will force me to cut back. The beds will also provide a handy framework for a duck tractor, trellising, and some poly-tunnels. I've really enjoyed the 2 beds I made this spring. They were constructed from engineered decking, and are each planted with rhubarb and chives at one end, with the rest dedicated to interplanted strawberries and asparagus. I love the wide path between the beds.
BTW, I had some purple potatoes for supper tonight. They were awesome. Hubby took one look at them, and said, "I'll pass!" Luckily, I also had some cooked plain ol' white potatoes. One of these days, I'm gonna force that man to eat supper with a blindfold on!