Building a permaculture banana circle​

Banana trees are very hungry plants, requiring lots of nutrients, light, and water. A banana circle provides optimal growing conditions for productive trees and is a beautiful addition to the garden. A deep hole is dug and the removed soil used to form a ring-shaped mound. The bananas are planted on the inside rim with other productive plants. Woody biomass, kitchen waste, weeds, and any other organic matter is thrown into the hole, along with greywater (from the laundry and kitchen) to feed the plants. After a certain time, the bananas will generate their own biomass in the form of dry leaves and old tree stems after harvesting the fruit.

What does a banana circle look like? 

A central hole with both a radius and depth around 1 m. A wide variety of organic materials are thrown into the hole, including fallen logs and tree trunks (to provide helpful fungi and drainage at the bottom of the hole), followed by any mulch materials such as organic kitchen waste, weeds, leaves (green or dry), hay, manure, egg cartons, cardboard, and paper. 

A mound with both a height and width around 0.5 m made from the soil dug from the inner hole. If the local soil is poor, the excavated dirt can be relocated and good quality soil or compost used to form the rim. This is the garden area containing all the plants. The inner edge of the rim 7-8 banana trees are planted equidistantly around the ring. A tropical grass (e.g. lemongrass, citronella, or vetiver) is planted in between the bananas as a groundcover for the inside edge of the mound. A root crop such as sweet potato is placed towards the top of the mound as a general groundcover. Other rhizome plants such as ginger, turmeric, taro, and canna lily can be planted on the outside of the mound. The lemongrass, citronella, and ginger are fragrant plants that deter pests and mosquitos.

Conditions / requirements 

Bananas are demanding plants and have several important requirements for growth: 

1. High light conditions: the circle needs to be planted in an area receiving sunlight throughout the day without long shadows from tall far away trees if possible.
2. Abundant water: greywater from the kitchen, shower, and washing machine can be piped into the circle to recycle the water and provide added nutrients. Building a swale around the circle, digging a wide hole around the banana plants to collect rainwater and adding abundant organic matter (e.g. a good compost and soil) to this circle and inner hole will help retain water.
3. Nutrients: the large pile of decomposing biomass in the centre of the circle feeds the bananas, along with nutrients in the greywater runoff and any added compost. The bananas will also feed their baby plants with fallen leaves.
4. Space: banana trees can’t be put too close together, so usually 7-8 banana trees are used for a circle with a diameter around 2-3 m. 

Building a banana circle at Kadagaya 

In March 2016 we decided to experiment with a banana circle close to the house, as a way to recycle our greywater and provide a small kitchen garden with ginger, turmeric, sweet potato, yucca, and lemongrass.  

1. Clearing the area: We chose an area of old garden beds overtaken by the jungle. The first step was the clear the site down to ground level with machetes. It is important to remove all the weeds very well, especially the roots and wood stems of plants in the outer area that could regrow under the mound. We cleared an area around 2–2.5 m radius to give ample room for digging. Our central hole had a radius of 1 m radius with an additional 60 cm for the mound and another 20 cm for a swale (drainage trench). Hence the total banana circle had a radius of approximately 1.8 m.
2. Marking the circle: By placing a stake in the middle of the area with a 1 m string attached, we walked out the inner circle and marked it with powdered chalk.
3. Digging the hole: We dug down in a deepening spiral using picks and shovels. As our soil is mostly clay and heavy to dig, the spiral make the job easier as there was always an edge to dig down into. We left a pillar of earth in the centre so we could check the radius now and then with the string in early stages. The excavated dirt was thrown all around to hole to form the mound and intermittently pushed outwards to avoid it falling back in the hole (by erosion / rainfall etc.). Towards the end of digging, we knocked down the central pillar as measuring the radius was no longer necessary. Additionally, we left a small step to help access in and out of the hole and kept this area clear of dirt to make a walkway (which has remained after completion as it is useful for filling the hole without stepping on the plants. A swale (channel) was dug around the outside of the circle to capture more rainwater and distribute greywater from the house.
4. Filling the hole: Initially the hole was filled with woody biomass (dry and rotting logs, woody stems, trunks etc.) to provide drainage and fungal species. On top of this we placed a lot of green organic materials (weeds, grass clippings, and leaves). Every day the kitchen waste is thrown into the hole (which needs to be very well covered with dry material so as not to attract flies and decompose anaerobically (and smell).
5. Planting the outer rim: We planted eight baby banana trees (transplanted from elsewhere on our land) on the top of the mound in wide holes for water retention. Lemongrass (or a similar tropical grass could also be used) was planted on the very inside of the rim. Sweet potato was planted between the banana plants (at least 2 slips between each), with ginger outside this and turmeric on the very outside. After a month or so when these plants were established, canna lilies were planted with the lemongrass, pineapples around the bananas, and onions and garlic were spread throughout the rim for repelling pests.
6. Composting: The plants were thickly mulched with 10-20 cm of newly-finished 18-day hot compost. 

After a week or so (despite some good rain and watering every morning), many of the banana trees and turmeric plants looked wilted and very sad. The brown leaves died off and after another week or so they both started sprouting new leaves and sprouts from the roots. After a month the circle was looking lush and growing well without additional watering.