What are safe ways to protect my raised garden beds?
I just invested in some nice looking raised cedar beds for my yard. I'd like to preserve the color of the wood instead of letting it go gray. I'd also like to preserve them in good condition for a while, as they were not cheap! But I am totally unclear on the safety of using a stain, a clear seal, a stain with seal, and whether any of the above can be safely used inside the beds as well as outside. Can you please help clarify the muddled information I am getting from the Internet on this topic? I've been told everything from using regular Thompson's water seal all around to a seal and stain being fine to being advised not to touch the wood at all.
Multnomah County Oregon wood products
It's very difficult to keep wood from turning gray without applying a coating that has a pigment such as paint or a stain. UV light will 'bleach' the wood through most clear finishes. I've tried some coatings with UV inhibitors and didn't like the results - some cracked and peeled (a problem with any coating on wood that forms a film, like paints or varnishes) others simply didn't do anything - the wood turned gray within a year or two anyway. I'm sure the manufacturer recommendations of reapplying every year would help (but I'm too lazy for that!).
You might try a semi-transparent stain - see information from the US Forest Products Lab on Finishes for Wood Decks.
As far as treating the inside of the material goes, the best approach I've seen is to use a plastic barrier - that's what I've done in my home garden. I stapled thick (6 mil?) plastic to form a barrier between the soil and the wood. This is a recommended approach for pressure-treated wood (what I used) to form a barrier between the treating chemicals and the plants. I see no reason why it wouldn't work well with naturally durable species like cedar as well.