The Tropical Garden Assembly Manual - Keyhole Banana/Sweet Potato/Papaya Circle Garden
The tropics are usually seen as a rewarding and welcoming location, but as we have already talked about, this is not the truth.
You can mess up very easily and very quickly in the tropics, because of their fragile characteristic and how fast and intense nature is there. However, if you understand what you are doing and have a solid recipe for a garden, you can also be quickly rewarded.
There are a couple of gardens that can be made in the tropics. All gardens can become somewhat self-maintaining (you have to steward them and harvest), and as the garden matures, your labor decreases, and yields increase and mature. You will build soil, and restore the nature. As a side effect of your garden practice, you will revitalize nature. But only if you assemble it correctly.
The types of garden are:
• Keyhole banana/sweet potato/papaya circle garden (Garden Type Gangamma)
• Garden on Slopes (Dry or Wet Terraces)
• Wet Food patch
• Food Forest (Avenue cropping)
• Dirty Water Patch
Following is a recipe for the tropical or subtropical garden "type Gangamma" (named after a person by Bill Mollison) in an IKEA instruction format based on extensive research from Bill Mollison in Taiwan, the Philippines, and Hawaii that will transform your relationship with the tropics and your gardening practice.
In this edition, in 7 minutes or less:
#1 The Tropical Garden is a Polyculture Flywheel
#2 Components (1-4) of the Keyhole Banana/Sweet Potato/Papaya Circle Garden
#3 Management
The Tropical Garden is a Polyculture Flywheel
Think of your tropical garden as a flywheel. The initial push requires effort—bed construction, species selection, timing coordination. But once the system starts turning, each component accelerates the next.
• Mulch-producing plants have multiple functions: feed, and protect the soil, hold water, exclude weeds
• Nitrogen-fixing legumes build fertility, nurse other trees and crops
• Layered canopies suppress weeds and moderate temperature, use vertical space as additional yield
• Deep-rooted perennials mine nutrients from deep soil layers and break compaction
• Seasonal timing ensures continuous harvest (there can be a hungry gap in the tropics) and soil coverage (protects against leaching and erosion)
• Essential earthworks store water in the soil for the dry period in order for your trees and plants to survive this period, prevent water erosion, and create new gardening sites (terraces)
• Essential plant and tree nurseries supply cheap and adapted plants and trees for your garden
• Animal integration brings useful animals in that transform waste organic matter and excess grass or remains from your garden (cuttings or discarted plants) into nutrients for it. They also help you control pests and overgrown plants
Component 1: The Central Production Hub (Banana/Sweet Potato/Papaya Circle)
It creates a nutrient-dense core that processes organic waste, produces staple crops, and anchors your water infiltration system.
The banana circle is a composting system disguised as a garden bed. Organic waste breaks down in the center, releasing nutrients slowly. Papaya and banana provide quick yields (6-9 months). Sweet potato covers ground immediately, preventing erosion and weed invasion, and provides an additional staple yield.
Materials Needed:
• Wet paper, cardboard, or banana leaves (for base layer)
• Coarse mulch: logs, twigs, hay, rice husks, or sawdust
• Small amounts of manure, ash, lime, or dolomite
• 4-5 papaya seedlings (tall variety)
• 4 banana suckers (dwarf types)
• 8-10 sweet potato cuttings
• Optional: yam or taro tubers
Construction Steps:
Step 1: At the center of a 100 square meter area, mark a circle 2 meters in diameter.
Step 2: Excavate to create a dish shape, 0.6-1 meter deep from hollow to rim. Ridge the perimeter.
Step 3: Line the excavated area with wet paper, cardboard, or banana leaves.
Step 4: Fill the hollow with coarse mulch—overfill to create a slight dome. Add manure, ash, or lime in small amounts. Bank stones around the rim if available.
Step 5: Plant the rim:
• 4-5 papaya (evenly spaced around the circle)
• 4 bananas (between the papayas)
• 8-10 sweet potato (filling gaps)
• Yams or taro inside the rim if available
Step 6: Later (after 4-6 weeks), plant climbing beans at the base of papaya and banana stalks.
Timing
Plant early in the wet season when soil is soft enough to dig but before peak rains. This gives roots 2-3 months to establish before the dry season.
Component 2: The Keyhole Access System
It maximizes planting area, by creating a "least-path" design where the ratio of path area to bed area is the largest.
You can reach almost any point in the bed from the path without stepping on soil. You just step once during the growing season to reach the most outermost zone, which is no problem (read next step).
The sunken paths capture water runoff and direct it into beds.
Leucaena or Palms can be planted for high shade and mulch at the junctions of the keyhole beds.
Materials Needed:
• Sawdust or gravel for paths
• Soil for banking bed edges (10-20 cm high)
• Paper and mulch (same as banana circle)
• Leucaena or Palms (optional)
Construction Steps:
Step 1: Around the banana circle, create a sunken path 0.6-1 meter wide. Cover with sawdust or gravel.
Step 2: From this circular path, create 5-6 "keyhole" indentations—curved paths that extend outward like fingers.
Step 3: Each keyhole is surrounded by a raised bed 1.5-2 meters wide.
Step 4: Bank the bed edges 10-20 cm high to prevent water runoff.
Step 5 (optional): Plant Leucaena or Palms at the junctions of each keyhole (see image)
Step 6: Paper and mulch each bed with 30 cm of trodden-down, wetted mulch.
Timing
Construct during the dry season when soil is easier to move and shape. Complete 4-6 weeks before the wet season begins.
Component 3: The Three-Zone Planting System
Each keyhole bed contains three distinct zones, planted according to harvest frequency and access needs.
Zone A: Pathside Greens (Inner Edge)
Location: Within arm's reach from the path.
These are your daily-harvest crops. Keeping them at the path edge means you can gather ingredients without entering the bed. Perennial varieties reduce replanting labor.
Species:
• Chives and shallots
• Parsley, coriander, thyme, sage
• Celery, broccoli
• Edible chrysanthemum
• Chard and perennial spinach varieties
Planting method:
• Tray seedlings (8-10 cm high): Plant in holes burrowed through mulch, with a double handful of soil per hole
• Small seeds (lettuce, herbs): Scatter on 50 cm diameter soil lenses placed on top of mulch, 5-8 cm thick, covered with 1 cm fine soil
Timing
Plant at either end of the wet season—early (as rains begin) or late (as rains taper off). Avoid peak humidity to reduce fungal issues.
Zone B: Frequent-Harvest Crops (Middle Strip)
Location: 1 meter wide strip behind pathside greens
These crops produce over weeks or months. Accessible from the path, but you're not harvesting daily. Staking and trellising on tree legumes (planted at bed junctions) provides vertical structure.
Species:
• Tomatoes (wilt-resistant strains)
• Eggplants, bell peppers, chilies
• Bush or staked beans and peas
• Kale, corn, okra
• Amaranth (green and grain crop)
Planting method:
• Tray seedlings: Plant in mulch holes with double handful of soil
• Large seeds (beans, peas, corn): Direct-sow in mulch holes with soil
Spacing: Plant densely enough to shade ground but allow air circulation. For tomatoes and peppers: 40-50 cm apart. For beans and corn: 20-30 cm.
Timing
Early wet season: Tomatoes, peppers, eggplants (need full season to mature)
Late wet season: Beans, peas, amaranth (shorter season, can handle drier finish).
Zone C: Root Crops and Cut-and-Remove Harvests (Outer Edge)
Location: Outer border of keyhole beds, just beyond arm's reach
You step on the bed once—to harvest and replant. These crops occupy space for months, so placing them at the outer edge keeps high-traffic areas accessible.
Species:
• Long-term root crops: sweet potatoes, yams, carrots, potatoes
• Cut-and-remove crops: cauliflower, head lettuce, cabbage
Planting method:
• Root crops: Plant tubers or slips directly in mulch with soil pockets
• Brassicas: Transplant seedlings into mulch holes
Timing
• Sweet potato, yams: Plant early wet season (need 4-6 months)
• Potatoes, carrots: Plant late wet season (prefer cooler, drier finish)
• Brassicas: Plant late wet season (avoid peak humidity)
Succession strategy: After harvesting root crops, immediately replant with fava beans or dahl (dried beans/lentils) to restore nitrogen.
Component 4: The Barrier and Mulch System
What it does: Prevents weed invasion, produces continuous mulch, provides windbreak protection, creates microclimates, and produces forage for animals, or food.
The whole garden can be fenced to exclude wild animals, if necessary.
Inner Barrier (Between Keyhole Beds)
Species: Lemongrass (Cymbopogon citratus) or Vetiver grass (Vetiveria zizanioides)
Planting: Thin strips separating each keyhole bed
Function:
• Cut 3-5 times annually for mulch
• Roots prevent kikuyu grass and rodent invasion
• Does not seed or spread aggressively
Middle Barrier (Periphery Ridge)
Species: Lemongrass, comfrey (Symphytum officinale), arrowroot (Canna edulis)
Planting: Strips just outside the keyhole bed edges
Function:
• Forms kikuyu grass barrier
• Comfrey: deep-rooted, mines nutrients, produces mulch
• Arrowroot: edible tubers, erosion control
Outer Hedge (Windbreak and Mulch Production)
Species: Cassava, banana, papaya, pigeon pea (Cajanus), Leucaena, Crotolaria
Planting: Taller border behind the middle barrier
Spacing: Dense enough to form continuous hedge but allow light penetration to inner beds
Function:
• Annual mulch production (eventually self-sustaining)
• Windbreak protection (critical in hurricane zones)
• Forage for chickens, rabbits, guinea pigs
• Cassava and banana provide supplemental food
Timing: Plant early wet season. Mulch, manure, and water heavily for first season. Once established (9-12 months), requires minimal care.
Fence
Constructed: Post and wire, electrified, dry stone, spiny woven hedge
Function: Exclude wild animals.
Management
• Replant all beds as you harvest them.
• Add a top mulch of straw, sawdust, bark, dry manure annually.
• The plants from the Component 4 (barrier and mulch production), like vetiver, and • lemongrass, are cut 3-5 times per year for mulch.
• Worms and good soil will take 9-15 to develop, but you can expect a harvest on the first season.
• Compostable materials can be placed under the top mulch layer.
• Small livestock, like rabbits, guinea-pig, and chickens, can be fed from weeds, waste vegetables, household scraps, and forage greens from the border hedge.
Most gardeners see this as "a lot of work upfront." However, it is the setting up of a flywheel, which is a system that accelerates itself, based on renewable living technology.
You're building:
• A nutrient-cycling engine that replaces fertilizer dependency
• A water-harvesting system that survives dry seasons
• A weed-suppression mechanism that eliminates constant clearing
• A microclimate moderator that buffers temperature and wind extremes
• Easy to build and maintain garden that can be built on any substrate
• A knowledge base that teaches you to overcome the fragility of the tropics, and steer its intensity
