Sunday, January 16, 2011
Biochar as fertilizer
Wood ash is a great source of potassium and other trace elements that can be lacking in a vegetable garden, but use it with caution! The pH of ash is quite high; too much can burn plants. Used wisely, it can treat unwanted acidity in the soil (a potential problem in my "Lasagna" method of gardening). Aviod using it on blueberries, roses, rhododendrons, and other acid-loving plants. I have yet to start testing the pH of my garden, but it was time to deal with the full ash can, so I sprinkled a bit of ash on areas where I plan to plant low-pH-favoring plants, and then enlisted Katherine and Scott in filtering out the biochar.
Biochar (charcoal used as fertilizer) has all the benefits of ash, with less pH action, and a heap of slow-release carbon. To separate it out, we passed about 15 gallons of ash through hardware cloth and ended up with about 3 gallons of biochar. We have a few more months of wood stove weather left for me to determine how much ash I still need.
Research using biochar on a larger scale in tropical soils is helping boost crop production and reduce deforestation. Check out more about it here: www.biochar-international.org/biochar/soils