Hi! I can't speak to Q 1 and 2 because I used tires for my raised beds. No problems with deterioration and free.
3. Yes. Use it on the bottom or mix it into your final planting medium.
4. I had very good luck with composted bedding and manure from a local farm mixed with peat moss and sand. This year I am not going to buy peat moss and will use shredded leaves and sand, but you can also use straight compost.

can' comment on the timber used or treatment of it, but for me i'd think very very carefully before using anything like tyres.

but yes put anything you have on hand in the bottom layer of the beds, we prefer mushroom compost as our main medium ingredient, but if you can't get that then sources any composted organic material lots of local rubbish dumps have material they compost for sale some for free.

you can check our pic's etc to see how we do our beds.

len

Here is a link that might be useful: len's garden page

I've used Thompson's Water Seal on my raised bed boards. I used 2 x 12's stacked two high making my beds 21 inches high. I buried my bottom boards two inches deep. Those boards lasted eight years before they needed to be replaced. We removed one board at a time, when the old boards needed to be replaced, and set a new water seal treated board in its' place. Worked well. We used 4 x 4 posts at the corners for strength and attached the boards using L brackets. When using water seal be sure to paint every surface area, inside, outside and the end grain portion of the board. We used several coats, allowing the boards to dry between coats. As I said we got 8 years out of those boards.

Carole

Here is an informative article on using old tires in the garden. I've heard everything from they smell to they're a fire hazard. Well they don't smell and they're only a fire hazard if YOU LIGHT THEM ON FIRE! Why not recycle them? And another thing, once they plants start growing you can't see the tires for those who need a 'pretty' garden. Tires hold the moisture in and allow the soil to warm quicker in the spring.
http://www.backwoodshome.com/articles2/sanders98.html

Oklahoma State University did some research on raised beds some years ago using old tires as the borders. In this case, they cut the tires, and trimmed them so that when stretched out, it was a semi "lumber". I looked, but can't find the link that shows them. As i recall, they worked pretty well.

I've used old treated 2x8s that came off of a replaced deck. They've been on the ground for about 10 years and work well.

A friend of mine who has a raised bed garden mentioned to me that next time he uses wood for his box he would also put a plastic liner. Apparently he had an old swimming pool that could be used for the liner. The concept of keeping the soil from making contact with the wood would slow the decomposition of the boards.

I use regular untreated lumber without any water seal or plastic or anything and they're five years old so far. There's no signs of rot yet so I'll probably get even a few more years out of them.

My beds are mostly 2x12s with 4x4s in the corners. You may want to rethink those 1x12s and make them a little thicker.

Unfinished compost (leaves, grass, etc) makes for a great way to start a new raised bed. It'll continue to decompose so you may have to top it off next year because it'll look half full by then. But my veggies have done great in unfinished compost covered with soil or finished compost.

Here is a link that might be useful: Raised Garden Bed Pictures

Here we have been using raised beds, four by eight feet, made of two by eights for many years. We go to the local sawmill and get new, rough sawn lumber at a very reasonable price. I agree with Cambs7. They last for eight or ten years here in coastal MA. Don't paint them with anything. It takes a year or two for the sap to dry up and another five or six to rot to the point of needing replacement. At my advanced age, I figure my garden has one more replacement left in it.

1. Can/should I stain the 1x12 wood?

Yes you may. Do you want to? probably not for edible crops.

I use regular fir 2x10 lumber, with no treatment (you'll probably have fir, not pine as you mentioned). I'm on my second year now and there is absolutely no sign of rot. The wood changed from.. 'wood' colour to a beautiful silver. I expect at least 5 years of service, at which point i'll unscrew and replace the wood as necessary. Wood where I am from is cheap.. about $6.00 for a 12' 2x10.

2. Can/should I use Thompsons Water Seal on the wood?

Again, you may - but I wouldn't. It's a chemical you don't need in your food. Wood that is in direct contact with the soil is still going to rot. Thompson's might prolong that a bit, but it's not magic. Skip it.

3. I also have a large pile of leaves/grass/compost the corner of my yard that I was thinking of lying down on the bottom 2-3" or so of my vegetable garden on top of a layer of cardboard.

Should I use that pile of leaves and grass that is semi-composted on the bottom of my vegetable bed?

Sure, spread it out among your beds, mix it with the soil you're putting in there. It'll help condition your soil. You don't need the cardboard.

4. What is your best suggestion for a top soil?

Compost is your base, then you can add materials as necessary to improve drainage, retention etc. You can use mushroom manure (which is actually spent soil from the cultivation of mushrooms) It lacks in the big nutrients like NPK, but remains high in the trace and mineral nutrients. Add some additional fertilizer or mix with the compost in your yard - get's better with age.

Go to www.woodfinder.com and search for roughsawn locust. It's pretty much impervious to dirt and isn't going to rot in your lifetime. You won't have to treat it but you will have to pre-drill holes. It's very hard.

Flatlander - Was it a Noble Foundation article instead of an OSU, maybe?

Here is a link that might be useful: Raised beds

soonerg: I've read that article and while interesting it looks like alot of work. I used the methods described in Paul Farber's tire recycling book. I've used alot of the ideas in the book in my garden, last winter I made the tire composter and placed in right outside the cellar door and that was really handy - I didn't make one this year and I'm sorry. Attached is a link to Farber's web site.

Here is a link that might be useful: Tire recycler