Keyhole Garden

A keyhole garden is a small round growing bed with a wall around it and a slot cut into one side, so from above it looks like a keyhole. Standing in the slot puts the gardener within arm's reach of the middle, and the soil is never walked on. At the centre stands an open basket kept filled with kitchen scraps and garden waste. Water poured in, and compost rotting there, spread outward through the bed, so what feeds the garden sits inside it. It is built where the ground itself will grow little - rocky, shallow, dry or compacted - because the growing soil is brought in and held by the wall rather than repaired in place.

Two dimensions decide whether it works. The bed stops at about 3 m (10 ft) across, not for looks but because every part must be reachable from the notch or the rim; wider and somebody stands on the soil. The basket is roughly 30 to 40 cm (12 to 16 in) square and about 1.3 m (4 ft) tall, lined with straw so the compost stays put while water runs through, and lidded to hold heat and cut evaporation. Wall height is set to the person who will use it, because a height that is comfortable for one gardener is out of reach for another.

The basket must be fed continuously or the bed starves; it is the only fertility the bed gets, and a household producing little organic waste cannot run one. Washing water can be poured in and left to filter out through the compost and soil, though the design allows that rather than treating the water. The fill is the part with a limited life, productive for about five to seven years before it is renewed or the bed rebuilt, while the wall is durable and has come through storms intact. The siting has one cost: a dry raised cavity beside a doorway is what a rat wants, and in wet weather it shelters rodents and draws pests. It also competes for the same scraps as a compost heap, so a site running both divides one stream.