The dirt sides under the frame provide an avenue for roots and such to get into the raised bed-to-be, and we would like to prevent that. Plus we need a way to raise the bed over the surrounding ground level, maybe by 10 to 16 inches.
Our solution is to use corrugated steel sheets. These can be bought in 8 foot lengths, and cut in half will then provide 4 foot lengths. A 4 foot long sheet can be attached to the wooden frame so that 14 inches is above the frame, and 32 inches then extend down into the ground.
We cut the 8 foot lengths in half by using a thin metal cut off wheel for our hand power grinder. That works pretty well. Not a perfectly straight edge, but I can put the cut edge down and bury any issues with that edge -- the exposed, top edge is perfectly straight.
We use standard roofing screws, 1.5 inches long, to attach the corrugated steel to the frame.
Three sheets along the back wall. The first one put up was bent, length-wise, to fit in the corner, so we have the back wall, plus part of one side wall. We do the same on the other corner and can continue along the sides.
Then we run into a problem. Caused by poor planning. We started at the back. The ground, even the rock layer that we have dug down to, slopes gently from the front to the back. So the 32 inches of depth that we have in the back, reduces to less at the front. The result is that the sheet we want to put on the side, again showing only 14 inches above the frame, hits the rock floor with too much showing above the frame -- 15 to 16 inches -- and won't go lower. We could get out the grinder and cut each sheet to be shorter. Or we can get out the jack hammer and make the ground lower (at least in a line under the sheet metal), or we can raise the frame.
We decided to raise the frame.
Doing that, we can then continue around the bed, attaching the sheets to the side and the front.
Three more sheets to attach, and once that is done, we have the complete definition of the new raised bed.
There are a couple of details. Notice, that the corrugated steel sheets are, well, corrugated, but the frame is not. There is a special piece of trim sold at hardware stores for this, called a closer.
Before attaching the sheet metal, I first tacked the closer onto the frame, and then screwed the sheet metal thru the closer into the frame. It turns out the waves of the closer are a bit closer together and more "wavy" than the sheet metal. So if you force the low spot of the sheet metal into the low spot of the closer, you accordion the sheet metal a bit more and it molds to the closer shape.
The other detail is that the ground around the frame has collapsed in spots. This is most likely because I dug out a bit too much under the frame, combined with the fact that we raised the frame to get it level and high enough for the 48 inch height of the sheet metal.
We will need to fill in and smooth out these areas, after we fill in the raised bed with dirt. At this point, the raised bed has some dirt in it, the dirt that we never bothered to remove from the pit after we had dug it out.
We add on top of that all the dirt that we dug out and put in a pile in the back yard, mixed with a lot of leaves and grass. This gives us a clean back yard
and fills the new bed up almost to the point where the screws are that hold the sheet metal to the frame.
We still need 14 to 16 inches of dirt to fill the bed to the top. Since the bed is roughly 65 inches by 90 inches, that means about 2 cubic feet more of dirt.
