Written by Doug Crouch

With the constant downpours that never cease to amaze us how loud the pings can be on the tin roofs, the rains of the tropics are both a blessing and curse.  The rains are one of the main leaching forces that limit the tropical soils depth and subsequent fertility.   They are very seasonal in most places and form the moisture that creates the abundant soil and atmospheric humidity for constant microbial breakdown of organic material.  With these rains, the intense tropical sun, intense microbial breakdown, and swift winds from times, the humus content and fertility is limited in the tropics. On this page and the others called soil building techniques we will pay particular attention to a combination of techniques that can bring fertility to the soil.  Without it, they quickly become exhausted and the collapse of the soils brings infertility, disease, and insects.  This is the common reason for so much slash and burn agriculture in the tropics and other natural capital degrading agricultural practices such as the use of synthetic fertilizer and pesticides.  Thus we must use techniques for water harvesting to lessen this erosive force.  Earthworks are the first technique that Bill Mollison laid out in his tropical chapter of the Designer’s Manual that forms the skeleton of this “blook”. They have been employed for millennia to deal with this flow and can be seen in the following major forms in the tropics:

  • Swales
  • Terraces
  • Pond Edge Manipulation
  • Sponges including Banana Circles

Creating spaces for waters infiltration is our main objective for creating swales.  These ditches and mounds that lie on contour, aid in slowing, spreading, and sinking water.  The use of contour asks a force to conserve water rather than the traditional method of sending water away.  The infiltration of water into the ground is extremely important for building soil in the tropics because without it the erosion picks up our hard work of building soil.  Remember to start at the top of your hillside and in the tropics we often need successive earthworks to deal with the tremendous potential of the water.  They are spaced much closer together than ones in the drylands and often are large in size.

Trees should always accompany the earthwork to stabilize the soil and cycle the energy of the infiltrating water.  Plants can be staked in space and time with the use of biological resources conveniently used to build natural capital.  Swales can be created by hand or with machines and can connect to other earthworks such as ponds.

Terraces on a steep hillside creating planting space and access


Terracing has long been used by humans to create access and planting space on hillsides that would normally be nearly impossible to cultivate.  The technique requires a skill we often lack these days which is to build with dry stacked stones.  Some of the existing terraces of complete territories like those in the Minho Valley in the North of Portugal should be revered just as much as any modern skyscraper or famous building of antiquity such as the Parthenon.  The leveling process requires a good eye and muscles but is not impossible.  It just takes time and the skill to stack stones with no mortar hence our needs for rural skills centers as the traditional fails to be passed on.  The walls continue to deteriorate as well and the work of centuries is failing in places like Northern Italy.  This truly is a loss of natural capital that our European forefathers created but in one generation has been lost.

Asian Rice Paddy’s showing contour

The tradition of terracing hillsides to create level areas for cultivating rice is an impressive use of contour.  With waters undeniable ability to show this facet of nature, contoured hillsides have long been used to produce staple foods.  Here the photo shows different times of planting and draining with the red earth exposed while others are flooded and others have the green growth of rice.

Permaculture Pond edge manipulation

Pond Edge Manipulation

After a pond is constructed one can also crenelate the edges of the pond for increased interaction between land and water.  This edge is abundant and allows for added growth of wetlands plants that can be cycled to the surrounding earth.  Lowland soil rich in organic material was also cycled into nearby beds.


Sponges facilitate the development of nuclei to merge in small scale intensive systems as system succession progresses.  The system uses ditches and mounds to create a diverse space thats edge creates numerous niches and

Papaya Sponge Permaculture with household waste being cycled

Papaya Sponge Permaculture with household waste being cycled

subsequent functions.  The depression acts as a space for the never ending flow of organic material that stems from life in the humid tropics.  It creates a safe haven for the organic material that is often discarded or burned in accordance with long standing traditions about cleanly spot around the house.  The copious amounts of tropical food waste may also be processed by the sponge as the outflow is compounded by subsistent agriculture movement.  The depression hold constant water and fertility aiding the associated plant tapping downward from the perched bed space.  The cycle is filled completely with good design.


Sponge Gardens, like a banana circle, where there is a depression where mulch is heavily layered and crops grown on the raised beds of the earthwork. Great soil building technique in the tropics.

The sponges can also be a greywater system in the humid tropics.  Often piping simply is out the back of the house and not necessarily designed for its maximum use.  This can be altered with some extra piping and proper placement of the sponge.  The carbon material will happily feed on the soaps and organic material while the plants will also never get dry.  Reportedly in reforestation in the drier regions of Haiti this technique has worked great fro establishing banana’s.  This is a great testament since that area of Haiti has no soil and very little rainwater distributed evenly over the year.

Greywater Permaculture

Mollison, B. (1981) Permaculture: A Designers ManualSisters Creek, Tasmania, Australia. Tagari.

Written by Doug Crouch

Header Art Anita Tirone

tropics header contour-2


  1. Concerning swales in the tropics, it is mentioned above ” They are spaced much closer together than ones in the drylands and often are large in size.” Can you give me an idea of how much larger and how much closer? I live high in the mountains of Costa Rica and am beginning the daunting task of putting swales in on a fairly steep mountainside. Thanks, any info is appreciated!

    • terraces on slopes greater than 15-20 % are generally recommended, but in A.Samoa, hillside ditches and vetiver grass barriers are working on slopes of 25%.
      to best plan for your site, we need to know size of site, slope, aspect, rainfall amount and distribution. what is off-site upland area contributing to water moving through your property?

  2. I am planning to design my land in Philippines which is about a quarter of an acre. The land is karst with a limestone slight elevation on one side. The other has good growth of plants and trees. Can I use swales and if so at what distances? Or better many banana, papaya and coconut circles? I want to retain as much water as possible in a small space.

    • you can use swales if you see runoff on the surface of the land especially that which is coming from a road or roof. Direct that into swales. O`often in the tropics they are spaced very closely but it depends on your watershed above. You can always dig one at the top of the hillside and see where that leads you. how much infiltrates, then dig more at say a distance of 3-7 m apart depending on your space. then also do add the banana circle design no matter what cause its such a great one and will help to retain water as well.

  3. Swales are one barrier option, as are vegetative barriers (lemon grass or vetiver grass or ginger), a limestone cobble dry stack low rock wall, or hillside ditch or any combination of these options.

    slope and soil type are critical considerations for spacing of any conservation barriers. with rock or veg barriers these should be contoured at >2% along the barrier. depending on your needs, you can either just trap overland flow and spread the water out behind the barrier to allow it to infiltrate, but make sure you provide stable outlets at the ends of the barriers. or you can channel is to a side or centerline ditch and move water off the slope to a stable low-lying landscape position.

    as you have a patch of vegetated ground at the low end of your site, you could also collect water in an upland water in an impoundment/pond. you could grow more water intensive crops then! do you think you can grow wetland crops (i.e. taro, rice, kangkung)?

    do you just need to move water off site from limestone uplands cause you have too much
    do you need to increase rainwater infiltration and reduce water moving off-site or to reduce flooding in low-lying portion?

    for steeper slopes, more closely spaced barriers are necessary. but on a quarter acre, 10000 sq ft or so, and give the slope and soils descriptions you already provided….it should be relatively easy to design.

    before making specific recommendations, it would be better to know the site dimensions, slope, aspect, soils, annual rainfall, rainfall distribution throughout the year, even or bimodal?

  4. Terrific information. Thank you for that. I refer my PC students to your information as it is really good information. Bruce Bebe, Phayao Permaculture Center, Phayao, Northern Thailand.

  5. I’ve got a bit of a challenge on, how do I handle waterlogging and not a huge amount gradient/slope (there’s a little down to a river). I’m in the N Highlands UK at a place on Google Maps called Achentoot. The ground has 18″ or so of clay like top-soil and natural compacted crushed rock (I’m not a geologist) below. I think the water runs across the top of the buried rock.
    So far, we’ve an abundance of willow, now looking for other things. We moved up here in August ’17 so still reading the landscape.

    • I should say there’s very little in the way of nitrogen fixers and about 1,000 6-8 year old tree’s (plus a few babies I’m adding)

      • Well the UK and its climate and you soil type sounds like raised beds are in order. You can drain water away from your growing areas but then divert that into other systems like chinampas or ponds. You can use any biomass to build soil. Those younger trees are probably really thick or dispersed in the regeneration process. You can thin those and inoculate with mushrooms to break them down and then use that as compost or chip them to break down faster. You can fill the pathways with wood chips to make a walkable compost pile. many, many options.

  6. Never heard of chinampas before, fascinating! Thanks for the rapid feedback @cdoug_e. Now I’ve been puzzling, what is the best mycorrhizal fungi to aim for or does it not matter? I love mushrooms anyway so I guess it’s another level of stacking function but it would be interesting to hear if there’re thoughts in that area,

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