I built this for my parents. It's a hybrid between a small hugel bed and a stone wall. The purpose of the stone is threefold: to look pretty, to form a boundary wall to hold the soil in place, and to make it a bit harder for the horribly invasive periwinkle growing below it to overrun the bed and the area beyond. The stone wall part faces north. The southern side of the bed doesn't have a stone wall. Since the albedo of the local stone is probably higher than that of soil or leaves, the absence of stone facing south might make the bed warm up faster in spring. Mainly, though, I skipped building a southern stone wall because I was lazy.
The stone wall is built without mortar. The upper surface of every rock slopes inward, and so the soil prevents the rocks from sliding.
In the bed I planted two hazels (Corylus avellana) and a sapling of European ash (Fraxinus excelsior).
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First layer of rocks in place. Ditch filled with weeds and rotten wood.