This Keyhole was made of douglas pine and metal. The metal structure maintain the vertical boards durably, like the strapping of a wine barrel.
Once the structure is assembled, the interior is covered with geotextile, to retain the soil, and protect the wood. Geotextile is not placed on the inner circle to allow the transit of nutrients, and earthworms from the center that will host the compost, to the cultivated periphery area. The filling of the keyhole is done on the same principle as the raised beds. we place dead branches at the bottom, to retain water (they will also decompose slowly). Nitrogen materials (leaves, mowing) and carbonaceous biomass (dry leaves, branches) are then alternated to facilitate decomposition, with soil and compost layers inbetween. We water abundantly at each step.