I came across an article the other day on wikipedia about Terra preta. Has anyone used charcoal like this to enhance sandy soil, like we have in Florida? Does this really work, and what is the best method for applying it?

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    Rainforest soils typically include a lot of clays and iron oxides; have very low organic content and seriously leached of most mineral ions. This is probably different to your soil. I don't know of anyone trying to reproduce these recently discovered soil types today, but there is a lot of interest that it could be a method of safe carbon sequestration.
    – winwaed
    Jul 14, 2011 at 21:06
  • @winwaed low organic content and high leaching pretty well describes the sandy soil here in Florida. I think it's also fairly high in iron.
    – psusi
    Jul 14, 2011 at 22:11
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    I've never lived in FL but I assumed alkali soils (all those limey muds in the Keys) - rainforest leaching is from acids such humid acid.
    – winwaed
    Jul 14, 2011 at 22:16
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    @winwaed, everything I have read has said that humic acid is a good thing ( and Terra Preta is high in it but the surrounding soil is not ), and is one of the big reasons to add compost. According to wikipedia, humic acid allows the pants to take up the icons from the soil. The cause of leaching is lots of rainfall percolating down through the soil and carrying away the water soluble nutrients with it. Supposedly the charcoal helps retain the nutrients instead of allowing them to leach out.
    – psusi
    Jul 14, 2011 at 22:25
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    Yes the rain water is acidified by leaf litter (eg. Humid acid). The acids mobilize the mineral ions. Eg. Wikipedia's page on oxisols en.wikipedia.org/wiki/Oxisols . Also cf. Bauxite formation by the mobilization of aluminum from mafic rocks in usually rainforest environments.
    – winwaed
    Jul 15, 2011 at 1:00

3 Answers 3


There are people experimenting with biochar. Not the same as terra preta, but also a way to sequester carbon in the soil, and you can potentially capture and use the syngas.

I don't use biochar, but I'm interested in its uses and have been doing some research for some time. It does appear to have beneficial effects on plants grown in soil amended with biochar, but it's not a silver bullet.

Biochar is very low in nutrients, and if you apply it to the soil it can potentially draw nutrients away from plants. It is better to combine it with compost, manure, or some other source of nutrients.

This paper from the International Biochar Initiative describes some best practices for soil application, including discussion of:

  • Safety (storage, handling, transport)
  • Loss to wind
  • Loss to water erosion
  • Optimum particle size
  • Application rate, frequency, and method
  • Uses in various situations (agriculture, horticulture, pastures, orchards, etc)

Terra preta appears to be a bit of a mystery still, but there is a ton of literature on biochar available. (Do some googling, look at the references in the paper linked above, or check out the references in the wikipedia article on biochar.)


First, I have not personally used charcoal as a soil amendment.

Where and in what form would you be getting the charcoal?

Charcoal is highly alkaline, therefore unless a soil test report states you need to raise the alkalinity of your soil (and by what recommended amount), I would not add in such a highly alkaline amendment, doing so could very well have a huge detrimental effect on your landscape.

Generally speaking the best way to improve sandy soil is:

  • Add in plenty of organic matter eg Compost, Autumn (Fall) shredded leaves, well-rotted farmyard manure.

The more organic matter you can incorporate into your sandy the soil, the better.

Additional after thoughts & having re-read the linked to, "Terra preta" article

  • For the average homeowner (gardener), is it possible and feasible to get enough suitable carbon material into the ground?

    Up to 9% black carbon has been measured in some Terra preta (against 0.5% in surrounding soils).

  • It took approximately 1400 years to produce "Terra preta" that is today being observed, studied.

    Terra preta soils are of pre-Columbian nature and were created by humans between 450 BC and AD 950.

  • "Terra preta" also has nutrients such as:

    nitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn).

  • Those above nutrients can easily be added to the soil by the gardener. Before doing so, I would get a full soil test done by a Local Extension Office (or other local organization, company offering that service).

  • "Terra preta" also needs plenty of other stuff, carbon alone isn't the answer, it's just part of the answer (up to 9% of the answer).

    The processes responsible for the formation of Terra preta soils are:

    1. Incorporation of wood charcoal
    2. Incorporation of organic matter and of nutrients
    3. Role of micro-organisms and animals in the soil

My thoughts on the above 3 points:

  1. Refer to the first bullet point I made above (under "Additional after thoughts...")
  2. Can definitely be done by the homeowner (gardener), but is going to take a good few years to see results, if only limited amounts of those components can be added each year. Of course you can get almost instant results on this item, if you have the time and/or money to excavate and dispose of huge amounts to existing soil, then bring in bulk loads of the necessary material to help form soil approaching "Terra preta".
  3. Again, can definitely be done by the homeowner (gardener). Number 2 will by proxy take care of quite a bit of this requirement ie Healthy soil attracts "micro-organisms and animals". As a believe in compost tea, I would also say a program of compost tea applied to the soil will do wonders in adding and attracting "micro-organisms and animals".
  • The local garden store sells charcoal, which is also a form of carbon. From what I have read so far, it will not break down nearly as quickly as compost, which I have also been adding. To counteract the alkalinity I was thinking of mixing in a bit of sulfur.
    – psusi
    Jul 14, 2011 at 22:10

I use Charcoal as an amendment. I had a buddy that was doing soil research on Terra preta. I was interested and decided give it a try.

In my case I have a large Rubbermaid tub. On the edge of our property is a compost for lawn cuttings, been there for many years. I filled the tub about 1/2 full with it, sieved out the larger stuff, and added a bunch of worms. I couldn't use the same type of worm as they suspect in nature. But the normal red wiggler compost worms work.

Every few months I change the carbon in my aquarium filters, and during the summer I have a little kiln I made out of a can I use when we have campfires.

I grind up the charcoal and feed the worms like you would for compost.

I use this in pots and in my aquariums. When it's time to plant something I use as much as I need of the charcoal vermipost and mix with as much haydite as I need for the proper body. When a pot is done I mix the used soil back into the tub.

This seems to work because the worms are processing the ground charcoal (activated carbon) the same way or along with the normal soil as the compost what you feed them. Secondly, the Haydite ( an expanded shale product) not only has a similar function as the carbon for small particles, but the larger bits serve to hold a lot of space for air and beneficial bacteria to grow.

They find a lot of busted up pottery in the Terra preta soils. Enough above average to be sure that it was busted up and put there. They think that the worm process, the carbon, and the pottery bits all work together.

I find that in the past year or so that I have been using this I have seen at lest double the growth in my aquarium and slightly more then that with some transplanted houseplants. This spring I intent to try a raised bed with it to see how it fairs.

Anyway, that's my two cents ymmv

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