It’s a technique called Hugelkultur . It’s from a brilliant German permaculture (a way of designing living ecosystems to eliminate the need for external inputs) engineer called Sepp Holzer, although he started doing this well before the permaculture brand emerged.
We discovered a fantastic introduction to the benefits of Permaculture. It was written by Maddy Harland, editor of Permaculture magazine, and is full of great ideas to keep your garden thriving, including tips to make a garden on your roof, walls or a balcony if you don't have any other space available. You'll also discover the wonders of the "animal tractor" and "chicken greenhouse", designed to make your garden more efficient and self-sufficient!