Do charcoal properties vary with source and temperature? What properties are important to the gardener?
Charcoal’s chemical properties do vary with source and temperature. In the opinion of this author the single most important quality of charcoal to the gardener is the ability to lower acidity, also termed liming capacity or effective neutralizing power. This is easily measured in an agricultural laboratory as calcium carbonate equivalent (CCE). If you are growing acid-loving plants you will want a charcoal with negligible CCE, and purportedly this is true of Mulga (Acacia) wood, bamboo, and pine needle derived charcoal. If you are combating low soil pH and aluminum toxicity you will want a charcoal with substantial CCE. Oak and maple hardwood charcoal appear to have substantial CCE. Apparently Amazonian hardwood derived charcoal shares this characteristic. Raising soil pH has been identified as biochar’s most important contribution to influencing soil quality in the context of Terra Preta.
