The longest lasting protection comes from chemicals that soak into the surface (and nothing you do will affect anything more than the very surface) and affect the fungi chemically. These unfortunately tend to be unreasonably poisonous to people. Rot is powerful.

They also have fake wood made from recycled milk jugs. I hear they last forever and don't look plasticky.

The plastic lumber is supposed to last a long time, but is really very expensive. I considered going that route too.

I thought about lining the inside part of the boards with plastic stapled onto the boards but, I never did go that route, but I imagine that is a way to go. I don't' remember hearing about anyone's experience doing that. Plus I was really trying to cut down on use of plastic.

As I mentioned before, in the end I went with the Hemlock which was better than pine and not as expensive as Cedar.

Sorry, I don't have another suggestion.

Just wondering if it would be safe for food.

There are varieties of 30-year ground contact lumber available, but as someone mentioned, WET ground is NOT covered in the gaurantee.

If it were MY raised garden bed ...... I'ld re-build the beds with 3 - 4 layers of plastic barrier underneath and on the sides up against and stapled to 30-year ground contact lumber (protected from the wet/moist soil by the plastic) and on the outside for better appearance and to repel the worst of the insect population, a facing of cedar. Also, mulch with cedar chips in areas of the garden that can handle the changes to PH.

That having been said .... using concrete edgers or blocks as Donna mentioned looks nice too. Another method would be to take reasonably conditioned lumber and cheap (broken bags that are sold at discount) concrete and pouring your own walls and edgers. If they aren't meant to be a load bearing wall, you can easily get away with not using rebar or some other kind of interior structure.

I drilled holes in the bottoms and lined the holes with 1/2" hardware cloth. The things I planted in them did very well. I'm not sure how they would hold up over the winter. I'll have to wait and see. One I have raised up on several bales of straw.......which have held up perfectly over the summer. And the other I have raised on several cement blocks with wood on them. The ones I bought weren't cheap, but I'm sure you could find others cheaper.

Another option if you can find it, is juniper timbers. I edged my blueberry and asparagus bed with 6x6" timbers, and wanted to use them for the rest of the beds, but the farm store stopped carrying them. Don't know if something similar might be available in other regions.

If you paint your fence dark green or black is will look dressier. Putting a run of plastic hardware cloth around the base of the fence might keep out the critters.

Really a pretty site, good luck with it.

The metal sided beds are very interesting looking. I wonder if they increase the heat not only of the soil, but of the person trying to work around the bed? They do get hot in the sun, yes?