What is Biochar and how is it made?

This is a question we've been researching and answering lately.  In short, biochar is pulverized charcoal that has been inoculated with something good for plants.  Biochar starts with pure charcoal - not store bought briquets (briquets have other chemicals added to make them bind into that shape, so it is not suitable for biochar).  The charcoal is then pulverized and mixed in a solution with plant food.  Some things that have been used successfully to inoculate are compost tea, sea minerals and urine. 

Why would you want to put biochar in your garden?  The biochar is almost 100% carbon and has a microscopic structure that is full of pores.  Carbon is very reactive and very stable, so soil nutrients bind to it easily and stay in place (less leaching).  The pores then form the perfect habitat for microorganisms that take the nutrients and make them available to plants.  Because of the stability of carbon in this form, it remains in the soil for hundreds of years providing this service.  Talk about a good bang for your buck!

If you want to see the potential for biochar enriched soils, look no further than South America.  The famed Terra Preta soils of the amazon were built from biochar and remain some of the most fertile soils in the world despite hundreds of years of farming.

So now that you're sold on adding biochar to your garden, how do you get it?  The short answer for now is by making it yourself.  Its not widely commercially available.  Fortunately, it isn't hard to make.  I would recommend this site:  http://biochar.info/biochar.biochar-production-methods.cfml  They have a pretty good resource for different ways to build a biochar stove/kiln.

Thanks to a good friend, Michael Morley, loaning us his biochar burner, we will be experimenting with making our own soon.  The process with his burner goes something like this:

1.  Load the burner with small diameter wood bits.

Brushy bits to break up

Michael loading the burner

2.  Build a small fire on the top layer and light it.

3.  Put the top on so that the draft begins up through the barrel.

4.  Wait for the fire to reach all the way to the bottom of the barrel then shut off the vents at the bottom and top to stop oxygen from reaching the fire (note the dirt piled up around the base now to block air flow).

5.  Let the wood sit in the very hot barrel and char for 20 minutes or so (longer if the pieces are bigger).  Open the vents and pour water in to quench the fire (notice the water on the lid and steam rising from the barrel).

 

6.  Dump out the contents.  Separate any unburned bits from the char ash (they can be run through next time to finish).  You have char!

We blocked the air to the fire too soon on this load - lots of things were left unburned.  We'll know better for next time!