What do you mean by "protect" the garage? Would the soil be at the same level as concrete or masonry, or are you actually bringing soil up to your framing? Pressure treated wood between soil and siding doesn't protect anything, but it does make a nice sponge.

If there's a reason to use wood, double check with your local wood preserver, because around here direct soil contact voids the warranty.

The soil needs be brought up about 6 inches, the garage with vinyl siding sits directly on ground. I did not want to place soil direct against garage. What type of barrier can be used between soil and garage?

As stated, Soil can only be placed against a water proof foundation wall (presumably cast concrete, which is typical), but only then it should be a few inches below the top sill plate (the part where the wood? wall are then attached to the foundation). You need to leave some free-board for potential flooding rain splatter.....

You need to start with the house as the high spot and grade away from it accordingly. Instead of adding soil, cant' your remove soil somewhere to lower the grade?

If you have no other option, then a sump pump maybe needed. This is a high maintenacne option, and for the sake of a planting bed, is it really worth that much risk/trouble?

The grade cant be lowered, the yard already floods, House is located on a canal and you hit water digging 30 inches down. House is much higher than garage. To help prevent flooding and delay the inevitable (raising of garage). What kind of barrier could be used between garage and new graded soil. 6 by 6 - then gravel then soil? Any suggestions would be appreciated

Maybe you need to have a local professional like a registered landscape architect or other proven expert look at your situation, tell you what would be a solution for you.

Wood framing for a garage wall is not designed to act as a retaining wall, which is what you're essentially asking it to do. You would be putting pressure against the walls, and you'd be trapping water right up against them. I wouldn't put anything right up against the garage. Not having seen the site, I would possibly do a retaining wall about three feet out from the garage. Even at that, we're talking about water. It's going to find the lowest point, and if that point is your garage...

More to the point, how did you have a new home built with the garage in such a bad location?

The property is located in a flood zone and fema required certain elevations. Since the garage was an existing structure it was not affected by new fema standards. It was not financially feasible for us raise or build a new garage when the new house was built. Raising/jacking up garage may occur in the future.

What is the least amount of space required between retaining wall and garage? (The garage is basically a glorified shed to us - used soley for storage) Thanks for the help.