Monday, May 25, 2009

Horticultural carbon, terra preta and high performance horticulture in the humid tropics

I have received many enquiries about the horticultural carbon that I use to create the rooftop 'Secret Garden of 1 Utama'. To make it easier to deal with queries, I have prepared the following account, to be published in a journal. Please bear with the stiff format and language, which is a journal requirement.

Soils in the humid tropics tend to be highly clayey. Clay particles stick together to impede passage of water and air, and this is detrimental to root growth. Without sustained effort keep clay soils open and porous, tropical soils rapidly become unproductive. Growers resort to many different methods of farming on clayey soils. For example, vegetable growers till the soil after each harvest and pile up the loosened soil to form raised beds. During each watering session, water soaks in and drains out easily, thereby simultaneously renewing the supply of water and air in the soil. A good soil is analogous to lung tissue in that both have large internal surfaces to hold moisture and air. Unfortunately the effect of tilling lasts only for a few months.

Clay soil may be burnt over a hot fire, in the process of which it becomes crumbly (Holttum 1953). Burnt soil maintains its crumbly structure for up to one year, and such soil is often used for container gardening.

However, the most favoured soil for horticulture is garden black soil, which goes by the Malay name of tanah hitam (black soil). Black soil originated in household backyards where domestic waste was dumped and periodically burnt. The black colour was due to the accumulation of charcoal and soot in the soil over time.

Tanah hitam in Malaysia seems to be very similar the soil in the Amazon known in Portuguese as terra preta (black earth). Terra preta soils are very fertile and contain a high content of carbon (about 10%). They occur on sites that appear to have been permanent native settlements for centuries before their populations were wiped out by diseases brought in by the Europeans. It would have taken centuries of firewood burning on the same sites to have produced black soil in the vast quantities, to 2 m deep in some sites. The discovery of terra preta sites has created a lot of discussion in the Internet about its origin.

The development of horticultural carbon
Open burning has been prohibited for many years in Malaysia, hence black soil is no longer available. Needing a large volume of good soil to establish a rain forest in the ‘1 Utama’ shopping mall in Kuala Lumpur, I decided to make such a soil by mixing charcoal particles with soil. We made this soil by mixing normal clayey soil (mostly subsoil) with charcoal and coconut fibre in equal proportions by volume. The charcoal was conventional charcoal produced by the kilning of mangrove wood. This came in large hard pieces that had to be broken up mechanically. The resulting particles were irregular in size and difficult to mix with the clay and fibre. I then found a much better source of charcoal in the factory of a charcoal briquette manufacturer. Charcoal briquettes are made by compressing sawdust into standard-size briquettes for kilning. The briquettes, meant for the barbecue market, can be easily broken into particles, sieved to remove dust and graded into the desired sizes. We refer to the product as horticultural carbon (Ng, 2006). We use two sizes: 1 – 4 mm particles for potting mixtures and 5 – 12 mm for garden beds.

We have found that a mixture of equal parts horticultural carbon and clay soil is good for general purpose horticulture. A mixture of three parts carbon to one part soil is better for cacti and succulents that need exceptionally well-drained soil.

Horticultural carbon is half the weight of soil, so the mixtures we make are lighter and more porous than ordinary garden soil. The reduction in weight was an important factor in my next project, a garden on the roof of the same shopping mall, seven floors above the ground. This garden, known as the Secret Garden of 1 Utama is now open to the public at weekends.

The porosity of soil mixed with horticultural carbon greatly reduces the labour of weeding because the weeds can be pulled out easily. However horticultural carbon only holds half the amount of water that an equivalent mass of clay soil will hold. Its lower water-holding capacity, together with its porosity, means that horticultural carbon dries out much faster than clay soils. The drying of the soil medium can be very damaging to the roots of plants, hence we find it necessary to keep our medium kept moist all the time. This can be arranged in various ways, for example, by watering twice a day. In pots, we would recommend placing the pots on shallow trays to hold water.

Horticultural carbon does not contain nutrients, hence fertilizers have to be applied regularly.

Initially the carbon and clay particles remain separate though mixed. Gradually the carbon wears down and becomes integrated with the clay, with consequent settling of the soil mixture. The soil level drops and is topped up with pure carbon.

The performance of plants on horticultural carbon
Our most extreme experiment was to grow rice on 100% horticultural carbon in plastic basins. The basins, about 20 cm deep, were three-quarters filled with carbon particles and topped up with water. Rice seeds were sown direct on the surface. Our Indonesian workers, rice-growers in their former lives, all had a good laugh because “everybody knows that rice only grows on tanah liat (sticky clay soil)”. Well, our rice grew and produced a heavy crop of grains. We have now grown three successive crops. The roots form very dense mats. After each crop, the roots have to be dried out before the carbon particles can be shaken out and recovered..

For cacti and succulents, we use a mix of 75% carbon to 25% burnt soil in elevated beds. Some species thrive, but some still find it too wet, and rot when it rains daily. Nevertheless ours is the only decent-looking cactus bed exposed to tropical rain in Kuala Lumpur.

Begonias, calatheas, and aglaonemas grow well in 50:50 mixes on raised beds provided 50 - 75% of the sunlight is cut off using shade-nets.

Of temperate plants and montane plants, we have managed to grow apple, peach, plum, Magnolia grandiflora, Magnolia liliiflora, arabica coffee, azalea, camellia, day lilies and Platanus. It has been hypothesized that in the tropics, the high night-time temperatures raise the night-time respiration rate to a level that temperate plants cannot adapt to. We think a high carbon mix allows air (oxygen) to get to the roots more easily, making it easier for temperate plants to adapt. However the flowering patterns of temperate plants are disrupted by the lack of seasons. Some species do not flower at all (e.g. day lilies), some flower infrequently and sparingly (e.g. apple and plum), and some flower all through the year (e.g. Magnolia liliiflora and arabica coffee).

Where to see horticultural carbon in use
In Malaysia, the Secret Garden of 1 Utama in Petaling Jaya, occupying 0.25 ha of flat roof top 7 floors above the ground, is the largest display open to public view. Here are grown over 500 species of plants, including palms, orchids, temperate plants, flowers, spices, rice, cacti, climbers and grasses. Also in 1 Utama but on the lower ground floor, is a rainforest with some 50 species of timber trees growing on a horticultural carbon mixture. In Sarawak, the Laila Taib Ethno Garden of the Sarawak Biodiversity Centre at Semengok, Kuching, displays a good range of native herbs grown on horticultural carbon, most of them larger and healthier than in their original rain forest habitats.

Horticultural carbon in carbon sequestration
Since the Industrial Revolution, the amount of carbon dioxide in the atmosphere has increased significantly, to bring about global warming. The increase in carbon dioxide in the atmosphere is due partly to the extraction and burning of coal and petroleum and partly to the clearing of forests, which reduces the amount of organic carbon stored in forests.

Proposed measures to control global warming include reduction in consumption of coal and petroleum and the planting of trees and forest to convert atmospheric carbon dioxide into organic carbon. However, reduction in consumption has proven to be difficult, and trees and forests fix carbon efficiently only when they are in active growth, i.e. during their juvenile phase. When trees die, organic carbon is converted back to carbon dioxide through the normal processes of decay.

The conversion of wood to charcoal fixes carbon more permanently and the use of such carbon as a horticultural medium kills two birds with one stone. Horticultural carbon acts as a carbon store but instead of being just a passive store, its use as a high performance horticultural medium helps to solve the other global problem, of increasing food production in the world. On our roof top garden the average use of horticultural carbon is 1 tonne (equivalent to a volume of 2 m3 ) to cover 6m2 of floor area. Our manufacturer of horticultural carbon is

Holttum, R.E. 1053. Gardening in the Lowlands of Malaya. Staits Times Press, Singapore.
Ng, F.S.P. 2006. Tropical Horticulture and Gardening. Clearwater Publications, Kuala Lumpur.


Erich J. Knight said...

Dr. Ng,
What a wonderful sounding project, is there a site with video of the gardens?
I'm surprised your work has eluded me. Let me share with you my research & current links on developments for Soil Carbon Sequestration;

Biochar Soil Technology.....Husbandry of whole new orders of life

Biotic Carbon, the carbon transformed by life, should never be combusted, oxidized and destroyed. It deserves more respect, reverence even, and understanding to use it back to the soil where 2/3 of excess atmospheric carbon originally came from.

It's hard for most to revere microbes and fungus, but from our toes to our gums (onward), their balanced ecology is our health. The greater earth and soils are just as dependent, at much longer time scales. Our farming for over 10,000 years has been responsible for 2/3rds of our excess greenhouse gases. This soil carbon, converted to carbon dioxide, Methane & Nitrous oxide began a slow stable warming that now accelerates with burning of fossil fuel.

Wise Land management; Organic farming and afforestation can build back our soil carbon,

Biochar allows the soil food web to build much more recalcitrant organic carbon, ( living biomass & Glomalins) in addition to the carbon in the biochar.

Biochar viewed as soil Infrastructure; The old saw;
"Feed the Soil Not the Plants" becomes;
"Feed, Cloth and House the Soil, utilities included !".
Free Carbon Condominiums with carboxyl group fats in the pantry and hydroxyl alcohol in the mini bar.
Build it and the Wee-Beasties will come.
As one microbiologist said on the Biochar list; "Microbes like to sit down when they eat".
By setting this table we expand husbandry to whole new orders of life.

This is what I try to get across to Farmers, as to how I feel about the act of returning carbon to the soil. An act of pertinence and thankfulness for the civilization we have created. Farmers are the Soil Sink Bankers, once carbon has a price, they will be laughing all the way to it.

One aspect of Biochar systems are Cheap, clean biomass stoves that produce biochar and no respiratory disease. At scale, the health benefits are greater than ending Malaria.The biochar Fund
h t t p: //

The USDA-ARS have dozens of studies happening now to ferret out the reasons for char affinity with MYC fungi and microbes, but this synergy is solidly shown by the Japanese work, literally showing 1+1=3

Charles Mann ("1491") in the Sept. National Geographic has a wonderful soils article which places Terra Preta / Biochar soils center stage.
h t t p ://

Biochar data base; TP-REPP
h t t p

NASA's Dr. James Hansen Global warming solutions paper and letter to the G-8 conference, placing Biochar / Land management the central technology for carbon negative energy systems.
h t t p

Glomalin's role in soil tilth, fertility & basis for the soil food web in Terra Preta soils.

UNCCD Submission to Climate Change/UNFCCC AWG-LCA 5
"Account carbon contained in soils and the importance of biochar (charcoal) in replenishing soil carbon pools, restoring soil fertility and enhancing the sequestration of CO2."
h t t p

This new Congressional Research Service report (by analyst Kelsi Bracmort) is the best short summary I have seen so far - both technical and policy oriented.
h t t p
:// .

Given the current "Crisis" atmosphere concerning energy, soil sustainability, food vs. Biofuels, and Climate Change what other subject addresses them all?

Carbon to the Soil, the only ubiquitous and economic place to put it.
Erich J. Knight
Shenandoah Gardens
540 289 9750

Dr. N. Sai Bhaskar Reddy said...

Dear Dr Francis,

Your sharing of the experience and the Rooftop Garden trails are very inspiring and great.


I had been doing small scale rooftop experiments using biochar, the photos and experience is posted in this blog.
GEO is implementing a project in Semi-arid part of India, with support of Action Carbone from this month, Good Stoves and Biochar communities project.

Dr. N. Sai Bhaskar Reddy

Dr Francis Ng said...

I believe there is a video walkthrough of the Secret Garden of 1 Utama on the website of the New Straits Times:

It would be useful if those who have seen it could post their comments. I have not seen the video myself because I only have a slow dial up web access.

I must confess I was unaware of all the interest on terra preta (and biochar) until I was writing up this blog. Thanks, Erich for the web links.

Erich J. Knight said...

I found the video here;
h t t p://

However they had no place to comment on it.

The video runs very fast, and is out of focus alot, but yet your garden is quite beautiful and lush.

Yes much is happening with biochar and you should have presented your work at the Asia Pacific Biochar Conference 17 - 20 May, 2009

h t t p://

See: Australia and New Zealand Biochar Researchers Network

h t t p://

You guys in Asia and Australia are years ahead of the west with your biochar work.

Here's some more links, if your blog will accept them.

If not please email me at and I'll send you my full list

Thanks for your work

Biochar data base; TP-REPP
h t t p ://

Biochar Studies at ACS Huston meeting;

Most all this work corroborates char soil dynamics we have seen so far . The soil GHG emissions work showing increased CO2 , also speculates that this CO2 has to get through the hungry plants above before becoming a GHG.
The SOM, MYC& Microbes, N2O (soil structure), CH4 , nutrient holding , Nitrogen shock, humic compound conditioning, absorbing of herbicides all pretty much what we expected to hear.



665 - III.


Biochar SEA said...

Dear Dr. Ng,
I was very pleased to discover your blog and your activities related to soil carbon. I would be most interested to engage in discussion with you on future biochar initiatives in Malaysia and the South East Asia. I hope you can find the time to review the new Biochar SEA blog and I look forward being able to contact you directly.
Kind regards,
Trevor Richards

Dr Francis Ng said...

Today, the management of 1 Utama hosted a visit by about 30 children from an orphanage, ranging between 7 and 14 years. It being Friday, the Secret Garden was opened specially for them. Our normal open days are Saturday and Sunday. I soon found that the orphans did not have as much curiousity as more fortunate children, so I had to abort my garden talk and take them to the maize patch, where we had about 40 special hybrid plants growing on 100% horticultural carbon. The seeds had been sown directly on site and the cobs were just ready for harvest. The kids harvested one cob each. This variety can be eaten raw and is sweet and juicy. The kids had a great time, though some were very timid and had to be coaxed to twist and pull the cobs from the plants. I did not say anything about the carbon. They had to move on to their next stop, a fast-food burgher outlet. Besides, I do not think I could have described the significance of carbon in five minutes, or even half an hour.

Next Friday, I will host another group of children. These will be from yuppie 'member' families, and I expect they will be more curious and less timid. There will not be any more maize to harvest. We are going to show them how to grow rain-lilies from bulbs.

The LawMan said...

ahh, the power of the internet to put niche area experts in touch with one another...

Ranunculus said...

Dr. Ng,

It has been fascinating reading your blog and this is the first time I came across it. I went through all your previous blogs and was thrilled by the possibility of growing temperate climate plants in the tropical country like ours. I started planting apple seeds at the age of nine and the seedlings would grow about 3-4cms and eventually die off. Most of the time the seed germinates inside the apple in the fridge, and I would go "yo-yo" seeing the seedling. I never knew anything about the need of seed dormancy breaking etc. I would "transplant" it and become sad seeing it wither after a short growth. I could say I was obsessed with growing apple tree (from the Johny Appleseed story). I never succeeded, and I am in my mid thirties now, still obsessed with temperate climate crops. Although my profession is engineering related (and very much passionate with it), my love for planting seeds and seeing them growing never really withered. I had searched for Gardening forums in Malaysian webpages, but was really frustrated to find any that could provide the informations to help my "dream" for growing temperate climate plants in low land tropics. Your 1-Utama work inspired me most, and now I believe I can make something towards my "dream". I made a thesis for my graduate studies involving Solar Cooled Greenhouse for Cultivating Strawberries in Tropical Climate. It was a little expensive to do it in Malaysia in small scales, since solar cells, absorbers and system controls are very expensive here (ironically since we have a so called silicon valley!). I learned a lot in researching and writing my thesis and using engineering background to support the technical capability of the project. I am extremely happy to read your work and very much surprised that open system cultivation of temperate climate plants is still possible. I would definitely try the carbon earth idea in my coming real project. I am building a set of Peltier Coolers to germinate and cultivate strawberry, dianthus, persian buttercup from seeds and hopefully acclimatize them to the tropical weather. There is a lot of control involved in terms of humidity, soil chemistry, day-and-night temperature variations etc, but I am going basic. I know it will be tough, but I had been persistent since young, and reading your work makes me think that this could be possible. I will definitely read your future articles and visit your Secret Garden when I get a break. It was indeed a long search for a proof to make my crazy idea work, and it landed and ended on your blog. Thank you so much for the inspiration. One step forward is better than not making any steps at all.
Hope to read many more interesting articles from your blog and from those who comments.
Thanks to Mr. Knight for his excellent, lively and informative comment on Biochar.

Ranunculus A. Fad

Anonymous said...
This comment has been removed by a blog administrator.
Erich J. Knight said...

Dear Dr. Ng,

Here are some updates

All political persuasions agree, building soil carbon is GOOD.
To Hard bitten Farmers, wary of carbon regulations that only increase their costs, Building soil carbon is a savory bone, to do well while doing good.

Biochar provides the tool powerful enough to cover Farming's carbon foot print while lowering cost simultaneously.

Agriculture allowed our cultural accent and Agriculture will now prevent our descent.
Wise Land management; Organic farming and afforestation can build back our soil carbon,
Biochar allows the soil food web to build much more recalcitrant organic carbon, ( living biomass & Glomalins) in addition to the carbon in the biochar.

Biochar viewed as soil Infrastructure; The old saw;
"Feed the Soil Not the Plants" becomes;
"Feed, Cloth and House the Soil, utilities included !".
Free Carbon Condominiums with carboxyl group fats in the pantry and hydroxyl alcohol in the mini bar.
Build it and the Wee-Beasties will come.
Microbes like to sit down when they eat.
By setting this table we expand husbandry to whole new orders & Kingdoms of life.

This is what I try to get across to Farmers, as to how I feel about the act of returning carbon to the soil. An act of penitence and thankfulness for the civilization we have created. Farmers are the Soil Sink Bankers, once carbon has a price, they will be laughing all the way to it.
Unlike CCS which only reduces emissions, biochar systems draw down CO2 every energy cycle, closing a circle back to support the soil food web. The photosynthetic "capture" collectors are up and running, the "storage" sink is in operation just under our feet. Pyrolysis conversion plants are the only infrastructure we need to build out.

Another significant aspect of low cost Biomass cook stoves that produce char is removal of BC aerosols and no respiratory disease emissions. At Scale, replacing "Three Stone" stoves the health benefits would equal eradication of Malaria
The Congo Basin Forest Fund (CBFF).recently funded The Biochar Fund $300K for these systems citing these priorities;
(1) Hunger amongst the world's poorest people, the subsistence farmers of Sub-Saharan Africa,
(2) Deforestation resulting from a reliance on slash-and-burn farming,
(3) Energy poverty and a lack of access to clean, renewable energy, and
(4) Climate change.

The Biochar Fund :
Exceptional results from biochar experiment in Cameroon
The broad smiles of 1500 subsistence farmers say it all ( that , and the size of the Biochar corn root balls )

This authoritative PNAS article should cause the recent Royal Society Report to rethink their criticism of Biochar systems of Soil carbon sequestration;

Reducing abrupt climate change risk using
the Montreal Protocol and other regulatory
actions to complement cuts in CO2 emissions


The Ozzie's for 5 years now in field studies
The future of biochar - Project Rainbow Bee Eater

The Japanese have been at it dacades:
Japan Biochar Association ;

UK Biochar Research Centre

USDA in their 2 nd year;
There are dozens soil researchers on the subject now at USDA-ARS.
and many studies at The up coming ASA-CSSA-SSSA joint meeting;

Nikolaus has been at it 4 years. Nikolaus Foidl,
His current work with aspirin is Amazing in Maize, 250% yield gains, 15 cobs per plant;

My 09 field trials with the Rodale Institute & JMU ;
Alterna Biocarbon and Cowboy Charcoal Virginia field trials '09

( add h t t p to my links)

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Anonymous said...

I prefer using burnt rice husk. The resulting texture mixes very well with the normal heavy clay soil.

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Garden seeds said...

Thanks for the post mate you have written it very well.

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teehowe said...

Hi Dr Ng,

Can I use black soil/tanah hitam as a substitute for potting mix? I am new to gardening and got some good results with peat moss, but I think they are too expensive in Penang. I am looking for a good substitute.

The last time I tried pure "Tanah Hitam", the pot was waterlogged. Then I experimented with top soil+black soil (1:1), and got quite okay results, but the seedlings are growing slowly, probably because of the heavy clay.

I was thinking of using black soil+perlite+compost (1:1:1), but not sure if this is the right thing to do. Your advice is appreciated.


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