There is a good article on keyhole gardens (Keyhole Gardening
Unlocking the secrets of drought-hardy gardens
By G. Elaine AckerIssue: February 2012) in the Texas Co-op Power Magagazine which is on line. If you google "keyhole gardening" it will come up. One reason for the shape is to allow easy access to the center where your compost "bin" is. You water through the compost, hopefully sending nutrients into the soil. A neighbor I had once used a somewhat similar concept which she said was a Japanese style of composting. Small composting wire structure place in center of small home garden into which kitchen scraps were tossed. Really simple, but I don't know how effective it was, or where the idea actually came from. The keyhole garden is supposed to be water efficient, nutrient rich and protects from some animal browsing. It's an intensive gardening method.
