Once you've roughly achieved the desired fit for all 4 walls, begin finalizing the depth of your post holes. You'll find that, inevitably, just as you think you've reached the desired depth on one end, your carpenter's level will tell you that the other end isn't cooperating! Once you don't think you're able to dig much further, it's time to consider shimming the low end. Small flat rocks make good shims.
As noted earlier, I wasn't quite able to excavate the full 2-foot depth I had planned for my post holes. So I came to accept that the bottom 2x12 board for each of my 4 walls would not be touching the ground, thereby leaving a gap. But this didn't concern me for such a small structure. Here are the measures I took to render the gap harmless:
- I lined the raised bed (walls and bottom) with landscape fabric.
- When filling my raised bed at the end of the project, I used coarse material (leaves and sod) to plug the gap.
- Most importantly, I mulched all around the perimeter of the raised bed. The mulch will pack down and prevent any soil from spilling out of the raised bed.
In fact, considering my goals for the raised bed project, this setback actually has a positive side to it. How so? Well, remember, I desire not only a raised bed, but also an outdoor work bench (to be formed by the boards that will cap off the raised bed). The additional height I'm "stuck with" will furnish me with a more functional outdoor work bench (i.e., one closer to waist-level).
Now it's time to join the walls of the raised bed together and give the structure some stability. Join the walls together at the corners, using corner braces, as shown in the picture above. Next, take the dirt you dug out of the holes and shovel it back into those holes, tamping it down as you go (I used a scrap 2x4 board for tamping).
In Step 9 we'll begin the finishing touches....
