“You start with a bucket and then layer this biochar powder with any organic materials—kitchen waste, coffee grinds, or used diapers—it’s the same. For example, I did a project with my hair, nails, grass, cow manure, chicken manure,” Matzusaka tells me. Fill the bucket to the top and wait four weeks. During this fermentation time, microorganisms multiply, then it’s time to call the worms in for dinner. The fermented layers from the bucket are mixed with soil, and it becomes aerobic, and worms come to eat. The length of time involved depends on the organic material: for kitchen waste in summertime conditions, fermentation could take two months; during the winter temperatures in Germany, it would take a longer time. If human waste—i.e, used baby diapers—is the organic material, Matzusaka recommends waiting for one year; she explains that you typically need to wait two to three years if you do normal hot-composting, for hygiene reasons. For terra preta, Matzusaka claims that one year is enough time because the microorganisms, fungi, and bacteria work intensively on the organic materials.