Why it works so well
The design is basically a circular swale, and it works well because there’s only one place to mulch, feed and water, which serves many plants. It’s a good spot to put all your kitchen scraps, to use as a handy compost heap, and it can also take cardboard, paper and tin cans. It can make use of excess water run-off, or if water is scarce, greywater can be directed to the circle so water is reused.
On top of that, bananas grow well in a circle, and bear bunches on the outside. Both bananas and paw paws are gross feeders and thrive on nutrients from the decaying organic matter in the central hole.
So you get ample production of fruit, and root crops. You can also plant climbing plants like beans to grow up the banana stalks once they are tall. Volunteer plants like pumpkins and tomatoes are likely to spring up from vegetable scraps in the compost.
Step by step establishment
You will need about four banana suckers (preferably a dwarf variety, to allow easy picking), four to five paw paws and ten sweet potato runners; also newspaper and plenty of mulch material.
Start by marking a circle about two metres in diameter. Then dig a dish-shaped hole 0.5 to one metre deep in the centre. Mound the soil around the outside in a circular ridge. If you like you can dig a narrow inlet at ground level to collect rainwater runoff.
Cover the whole earth circle with wet paper or cardboard, or banana leaves. Fill the hollow with rough mulch material such as course twigs, leaves, straw, decaying logs, rice husks, etc. Add scatterings of manure, ash, lime, dolomite or other fertilisers. Overfill into a dome; it will sink down over time.
If stones are available you can bank them around the outside of the rim.
Now plant banana suckers at 60cm intervals around the rim of the mound. Pierce the newspaper and mulch layers and plant into the fine raised soil.
Alternate with paw paws, and fill the spaces on the top and outside of the rim with sweet potato. Ten or so plants will spread to cover the soil with their edible foliage. You can also use other root crops like cassava and Jerusalem artichokes. Comfrey can be interplanted as a green manure crop; cut the leaves and add them to the nutrient heap as fertiliser.
On the inside of the rim you can add shade and moisture-loving plants like taro and ginger.
Shower within, garden without
Your banana-paw paw circle can become an outdoor shower or wash-up area if you put a circular grid or wooden slatted platform over the mulch in the centre.
You can plan a mandala garden using the circle as the focal point. Wrap a circular sawdust path around the outside with keyhole garden beds radiating off it. Keep an access path to give entry to the banana circle.
This design can be scaled larger for communities such as schools and villages, and has proved useful in countries like the Philippines and India. Multiple circles with vegetable mandalas produce food for villagers, use roof runoff or reuse washroom water where water is a critical resource, and provide shady areas for people to sit outside.
Meanwhile it is something almost any of us can do in a back garden or bit of space. It is easy, effective and looks good too.