How to Assemble Dry or Wet Terrace Gardens in the Tropics

It's overwhelming to garden on a slope, because it is difficult to build beds, and they have the risk of becoming unstable, causing a land slide.

In the tropics, during the rain season, they turn into "mud avalanches" that cause property damage and kill many people every year. Nevertheless, gardens on a slope, known as terrace culture, are a quintessential tropical characteristic (think of the rice culture in Asia). If you have an effective practice, you can transform slopes into a productive sustainable garden and/or food forest, and also guarantee land stability.

Following, as we have been doing in this series, is the Permaculture path to cultivate thriving dry or wet terraces gardens in an IKEA instruction format, drawn from Bill Mollison extensive investigations and practices in slope country in the tropics.

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In this edition, in 6 minutes or less:

#1 The Tropical Dry or Wet Terrace Garden is a Polyculture Flywheel

#2 Terrace building Guide

• Section A: Wet Terrace Construction
• Section B: Dry Terrace Construction
• Section C: Project for very flat sites
• All Terraces

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The Tropical Dry or Wet Terrace Garden is a Polyculture Flywheel

The type of terrace depend on:

• How steep is the slope

• The type of soil (good drainage or poor drainage)

• How much rainfall

• What kind of tropical climate (wet tropics, or wet-dry tropics - see first letter of the series)

• How the terrace is built (hand-made or machine-made)

Once the terrace build type is decided (which will be discussed together with each type), you can create your garden:

• Forest crops for mulch, fodder, or food (food forest)

• Annuals

• Trellis

• Paddy fields (flooded field for rice or semiaquatic crops, like taro)

• Animal husbandry, like ducks, pigeon, poultry, pigs, or bees

• Fish, crayfish, shellfish culture

It is no wonder that many long-lasting cultures—particularly in tropical and subtropical regions such as Hawaiian loʻi kalo (taro terraces) and ahupuaʻa land divisions, ancient southern China, Philippines's Ifugao, Balinese Subak, Maya and Aztec, Sri Lanka's Tank–Cascade Systems, Japan—developed intricate terraced polycultural systems. These transformed slopes into productive landscapes, mitigating challenges like nutrient leaching and poor, highly weathered soils, while amplifying tropical advantages such as abundant rainfall and warmth, by slowing water, cycling nutrients in place, and stacking functions across the landscape.

You can transform any slope into a sustainable and rehabilitating space with these gardening practices.

Terrace building Guide

What you need to know before you start:

• Your slope angle (measure with a level and measuring tape)
• Whether you have access to a water stream
• Your soil type (clay or clay-loam is best)
• Your annual rainfall

Do you have a stream you can divert to terraces?

Yes, then you can build a wet terrace (go to section A).

No, then you can can build a dry terrace (go to section B)

Are you on a very flat site (less than 4°)?

Yes, then go to Section C.

Section A: Wet Terrace Construction

Step 1: Measure Your Slope

Gentle slope (2-8°):

• Terrace width: Can be wider
• Sets: Continuous series possible

Steep slope (>30°):

• Terrace width: Always keep them narrow (3.5-6.5 m / 12-15 feet)
• Sets: Build in groups of 6-8 terraces, then skip space-for soil stability
• Pattern: Stagger the sets (don't align vertically)-also for soil stability

Step 2: Mark Your Contours

• Start at the top of the slope
• Use a level or A-frame to mark level lines across the slope
• Mark the space of the terraces

Step 3: Build the Bunds (Terrace Walls)

• Dig into the slope to create a flat platform
• Use excavated soil to build a bund (wall) on the downhill side
• Make bunds strong enough to hold water

Step 4: Install Water System

Top terrace:

• Dig a channel from your stream to the highest terrace
• Water should flow continuously into this terrace

Each terrace:

• Create a drain outlet at one end
• Dig a sump (deep area) to regulate water level
• The drain should lead to the terrace below
• Install splash stones or splash plates to take out the impact of the falling water off the ground
• Optional: Make sumps deeper for fish/crayfish/shellfish cultivation

Step 5: Plant the Terrace Beds

Water-loving crops:

• Rice
• Taro
• Watercress
• Kangkong
• Water chestnuts

Section B: Dry Terrace Construction

Step 1: Measure Your Slope

Very flat (<4°):

• Consider raised mounds or ridges instead
• Skip to Section C

Gentle slope (2-8°):

• Build large contour banks or swales
• These develop gradually into terraces

Steep slope (>30°):

• Terrace width: Keep narrow (3.5-6.5 m / 12-15 feet) if hand made. If machine made, they can be made wider
• Sets: Build in groups of 6-8 terraces
• Pattern: Stagger sets for stability (unaligned vertically)

Step 2: Mark Your Contours

• Start at the top of the slope
• Use a level or A-frame to mark level lines across the slope
• Mark the space of the terraces

Step 3: Build the Terraces

• Dig into the slope to create flat platforms
• Build bunds (walls) with excavated soil on downhill side
• Make terraces narrow on steep slopes for stability

Step 4: Apply Deep Mulch

Critical for dry terraces:

• Apply thick mulch layer to terrace beds
• This keeps soil moist without irrigation
• Use mulch from trees planted on bunds
• Replenish regularly

Mulch sources:

• Tree legume leaves and branches
• Bana grass
• Bamboo leaves
• Palm fronds
• Crop wastes and straw

Step 5: Plant the Terrace Beds

Dry-adapted crops:

• Millet
• Dryland rice
• Barley, wheat, rye
• Brassicas
• Fava beans
• Amaranth, quinoa
• Lentils, peas, grams, and pulses
• Rape/mustard

In-crop mulches:

• Beans
• Clovers

Section C: Project for very flat sites (slope angle <4°)

Mounds and Ridges

When to use:

• Very flat land
• Very wet areas (for drainage)
• Or drier areas (for water retention)

How to build:

1. Mark out rows following slight contours
2. Dig soil from between rows
3. Pile soil into ridges or individual mounds
4. Plant on top of mounds/ridges

For wet areas: Ridges drain excess water

For dry areas: Ridges catch and hold water

Crops: Cassava, yam, cucurbits

Pits

When to use:

• Rainfall less than 76 cm (30 inches) per year
• Good soil drainage
• Dry savannah areas

How to build:

1. Dig pits where you'll plant
2. Fill with mulch
3. Plant into mulch-filled pits
4. Pits retain moisture and mulch

Crops: Cassava, yam

All Terraces

Step 6: Plant the Bunds (for both wet and dry terraces)

Bund faces:

• Mulch-producing trees
• Tree legumes
• Bamboo
• Productive fruit trees

Bund crowns:

• Clover
• Beans
• Comfrey
• Lemongrass
• Fruit crops

Step 7: Stabilize the slope with Vegetation (for both wet and dry terraces)

Upper 1/3 of the hill - the very steep slope of 30 or greater- (if you happen to have access to this area), terrace side borders, and between terraces should be planted

• productive and mulch producing trees

• cover crops

Alternative method for steep slopes is to plant contour strips of:

• Vetiver grass
• Lemongrass
• Bana grass
• Tree legumes between grass strips

• This last 2 steps not only guarantee soil stability but provide enough organic matter to feed animals, composting, and material to mulch. That is the secret for long term viability without dependence of external sources.

• Consider planting vine crops off bund faces. Ex: Chayote, cucurbits, beans, passionfruit, kiwi.

• Consider placing animal housing on the top of terraces to create a trickle down fertilizing effect from their manure.

• You can use your creativity and create your own practice. Some interesting examples are given in

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Can you imagine preferring having a slope to garden instead of a nice flat land?

It is, for sure, a difficult mindset shift. Nevertheless, slopes have been cultivated in history with huge success both in terms of productivity, and positive ecological impact. They also are very beautiful.

Have in mind: Almost every slope benefits from earth shaping for soil conservation.

So. You can effectively develop your own gardening practice on slopes and cultivate a thriving ecosystem on that ignored slope.

See you next Tuesday!

Alexandre and Marina

P.S.: In our next newsletter, we'll dive deep into the next type of garden for the tropics, Wet Food Patch and Dirty Water Patch. Both are in close relationship with the house and a game changer for self sufficiency.

Sources: Mollison, Bill, Remi M. Slay, Jeeves, Andrew. Permaculture: A Designers' Manual. Tagari Publications, 1988, pages 259-263 , figures 10.8-10.15