Then, determine what you would like to use for the anchors. If you built your garden bed out of lumber, you could use nails as anchors, spacing each nail the appropriate distance as determined by the results of the calculation in Step 1 above. If your garden bed is made out of a composite material (part wood waste, part plastic), I recommend using an anchor placed on the outside of the bed. Since my beds are 6 inches high, I used 12 inch metal spikes I bought from the local hardware store, pounding them into the soil directly on the outside of the garden bed.
The 4x8 foot garden beds I bought, for instance, are 4x8 feet from end to end. But when you connect the boards at the corners, you lose a few inches, so the interior dimensions of the garden bed are actually a few inches short of the advertised size. In my case, my beds have an interior dimension of 46.25 inches x 94 inches. I refer to these dimensions as Usable Length for the remainder of this article.
Some of the other benefits of raised beds are: reachable - less bending and stretching gives the gardener easy access and makes maintaining and harvesting less of a task to perform; drainage - because the soil is above the ground it will not become compacted during heavy rains and will drain properly in preventing water-soaked soil;
The first step is to calculate the dimensions on the inside of the garden bed, which is the length and width that is actually usable for planting. If you bought your beds from a commercial source, then chances are, the interior dimensions are probably a little less than the advertised size.