Within each box, we mixed the native soil which is largely clay with two bags of organic potting soil and 1 large garbage bag of already decomposing manure and wood shavings from our family stable. Be careful where you obtain manure/bedding combination. I have direct control over the pile, what goes in it and what the horses producing it are eating or not. For example animals can be routinely fed antibiotics or feed through pest controls, de-worming chemicals... you name it and this goes directly into the manure that is "composted" and offered for free at local stables and yards. This mixture was tilled with an electric roto-tiller until it was fluffy and well mixed.
The end result is a raised garden bed that looks like this. I back filled the cut away slope with the rock extracted from the ground to secure the wall from erosion and help with drainage. This particular bed housed squash and artichoke which did extremely well. You see the edges of branches from fruit trees growing on the terrace above.
These garden beds were easy to assemble and cost about $35 per bed... twice the size and a third the price of most of the commercially available kits we found. Additionally, they are not plastic, or PVC which can potentially leach chemicals into the soil.
