While volunteering at Cold Water Gardens in Milton, Florida, I helped to build a banana circle–which is basically a circular swale/mulch pit surrounded by banana plants.
*The circle is multi-functional, and can be used for food production, composting/soil building, and greywater treatment.
CREATING THE CIRCLE:
We then covered the bottom of the pit with wet cardboard and newspaper, and on top of that, added layers of mulching materials–including green cuttings from the garden, wood chips, some food scraps, and banana leaves–hosing down each layer as we went. We continued adding layers until the pile heaped just above ground level; it will settle overtime and with moisture.
Next we planted banana suckers every two feet around the rim of the circle, created another narrow/shallow swale around the outside of the rim, and topped everything with a few inches of straw.
The berm of the outer swale will be planted with paw-paws. The inside and outside of both berms will be planted with root vegetables such as ginger, sweet potatoes, and carrots; they will send roots toward the middle of the banana circle to feed on the mulching material (which is breaking down, creating nutrient rich soil).
In the future, a slatted, wooden platform will be placed over the mulch pit to create an outdoor shower–using the bananas and paw-paws as a privacy screen. (At this point root vegetables would not be grown).
Given their beauty and many useful functions, banana circles are a Permaculture Gold Star in my book!