The term “raised garden bed” gives a visual picture that can include many different designs. The vision that you have depends on your exposure to the concept of getting the garden above the ground in some way, often to satisfy the need to grow where there is no soil, perhaps on a porch, patio or balcony. Or the goal might be to avoid (nearly) impossible to work or contaminated ground. All are reason but I think that the most popular concept or visions of “raised garden beds” are to get the garden high enough to allow gardening without having to bend over or kneel.
Gardeners or would-be gardeners with physical limitations that reduce the their ability to bend or kneel can prefer counter height garden beds. Because I’m a “tweener” gardener (in between good and bad health), I can still bend and kneel sufficiently but would like to benefit from other aspects of raised bed gardening.
So, here is what I chose. I chose a Sandbox style with a cutout for access without having to stand in the garden bed. I confirmed that 4 foot width enables me to reach just beyond center from any side. I also thought of the appearance and determined that this is more attractive than a rectangle or square!
I selected a slightly sloped space, I trenched to make level.
My ground (dirt) is not the worse that I’ve seen but it’s bad enough that I would not attempt to grow vegetables in. It does not have enough biology in it, Wont retain water or nutrients, and it is difficult to penetrate. Think caliche!
I needed to provide for at least 12 inches of soil depth. I selected 2×12 standard lumber from local home improvement store. Although the ground (previously described) is difficult I knew that in order to achieve the desirable depth, that I would need to remove dirt from below the height of the boards. By doing so I actually doubled the originally planned depth.
For design and construction information see link below.
Points of knowledge 1. Soil beds that do not contact the ground will have more rapid (think unstable) temperature changes. If off the ground soil bed is a requirement for you consider a). as deep of a soil bed as you can develop b). build a skirt around the base to provide insulation. Maybe even adding insulation. Adding mass like pavers in the base might have some benefit but keep in mind that cold temperature are retained by the added mass too.
Points of knowledge 2. Larger is better! Not always true. Refrain from dimensions that exceed your reach. Unlike ground gardening the gardener can’t simply walk to a location in the garden bed… (especially a raised bed) You have to be able to reach it! If access will be available on all sides you can simply work with the length of your reach multiplied by 2 and maybe add or take away a bit to accommodate. a). Bigger and or deeper also means more soil! That also means more money (if you have to buy soil, amendment and fertilizer) and more work establishing the bed and maintaining it over the years. Note that you’ll likely not be tasked with removing soil but you will need to add it.