Dan Hemenway wrote to us after reading EDN 106. “By the way, one reason why charred rice hulls may work well in potting mixes is that any form of charcoal improves the capacity of soil to hold nutrients and release them to plants. No doubt you have been reading about the biochar ‘discoveries’ in Amazonia, though I read about the same properties of charcoal as a teenager in the 1950s in a book that was rather aged then. Since charcoal is something that can be produced in many 'undeveloped’ regions, often from wood that is too large for cook fires, it might be worth adding to mixes in further experiments.
“[Here is another useful idea.] You will find that rotted and pulverized sabal palm logs, shredded, make contributions to potting mixes that are way beyond what you would expect. It is a far superior amendment to peat. I would expect that other palm species have different rates of decomposition and different end results, but it is worth looking into, particularly with weedy species like sabal. The core of the logs eventually (and fairly quickly) breaks down into a black, humus-like material that is fantastic! I use the logs in our trials adapting chinampas techniques to local conditions, particularly for bed walls, where they last just long enough to stabilize the soil.”