Hugelkultur

Hugelkultur is building raised beds with a core of wooden logs or branches; the logs rot down over several years, both providing nutrients and creating airspace in the beds, such that the soil needs neither fertilising nor tilling. As the wood rots it also becomes spongy, and creates a slow-release reserve of water at the heart of the bed.

References: hugelkultur: the ultimate raised garden beds, The Art and Science of Making a Hugelkultur Bed.