ok so here is what i do its kinda like bio char but cheaper. i takes a 35 gal steel drum one that the lid comes off and secured on with a steel ring and cut log cookies about a inch thick. and fill it up about 3/4 full secure the lid and take out bouth bung caps to releve preasure. then use 3 to 4 ' logs around the barrell and catch fire and keep adding for about a half hour after the smoke comming out has stoped. and the smoke comming out catches fire also its a good time if you like fire. when finished let cool take lid off and fill with water to put out ebbers then i crush it up very small and till it in my soil. iv only done this in out door gardens not sure if it helps or hurts but if the myans did it. and the soil where they garden is alive and kicking after this long it might be good. ps any left over is great for bbqing and in my opinion better than store bought. ps make sure both caps are off the drum. i did it with just the small cap off and the preasure was pretty crazy about a 5 ' jet flame comming out the top. hope this helps

I use a lot of wood ashes in my compost. It's extremely beneficial for sprouts or anything trying to take root. Early Native Americans used to burn whole fields because it made them more fertile the next spring.

Hey Dust.... Coal or char coal comes from plants... there is one contradiction. Here is another for you. coal has nice amounts of phosphorous and some sulfer ( higher grade coal has more but we don't need large amounts) from the composition i would assume that the absorption of small amount would be fairly quick, lasting a few weeks at most i think. same i would consider for coal ash, one must consider with burning coal that you are polluting the air alot with it with isn't always the best trade off. go ahead question this simple path (dead plant matter + centuries and pressure = peat +decades = coal )