Bio-char – Use in garden

Q: I have read about the benefits of charcoal and how it has a positive effect on plant growth. I think it might have come from the bio-conversion center at the University of Georgia.

Is there any research on the benefits of charcoal and adding it to the soil or compost bin to improve plant growth? How much would you use and how should it be applied?

A: Much of what I know I got from this description of the UGA project.

and from this International Bio-char website.

The beneficial effects of bio-char are based on the very productive terra prieta de Indio soils of the Amazon, formed when native people burned trees and mixed the ash/charcoal in the soil.

As I understand the chemistry of the process, bio-char is very porous charcoal incorporated into the soil to increase its nutrient exchange capacity as well as to sequester carbon. Bio-char is not quite the same as charcoal briquet’s or as activated charcoal. But in general, they can all be used similarly.

Charcoal has microscopic holes in it, making it a great site for soil microorganisms to grow. The only commercial source of bio-char I could find is AgriChar, made in Australia.

Here, you can make it yourself by heating wood or other bio-mass in a barrel. You could also grind charcoal briquet’s into small pieces.

But even when you have the bio-char, little research has been done on how much to apply to soil. One guesstimate is 1 lb per sq ft…..which would require LOTS of charcoal for a normal garden.

Further, it is possible that bio-char may break down rapidly in soils different from those in the Amazon. Much rigorous research needs to be done to quantify the benefits, if any, of bio-char in a homeowner garden/landscape.