If we talking about permaculture we have to talk also about hugelkulture, from german hügelkultur translates as “hill culture”.
The hugelkulture is the practice of composting large woody material to create a raised garden bed. In this case we can use the excess amounts of woody garden wastes, for example pruning, brushwood or hedge clippings. The pioneer of this technique is Sepp Holzer that in is house in Austria starting to adopted it, though he didn’t use the word hugelkultur.
The technique involves digging a circular trench about 1′ (30 cm) deep and 5′ (1.5 m) wide, in the centre of which is dug another hole 1′ (30 cm) deep hole. The material is piled in. Turf (grass) is than stacked face down on top, then layers of compost, well-rotted leaves and manure, etc as available. The layers break down slowly and creating rich humus over four or five years. It is claimed that this is ideal for growing hungry crops such as zucchini (courgettes) or strawberries.
This technique is mainly used in soils where water is scarce and there is no trace of worms, which means no fertility of the soil.
As the years pass, the deep soil of the raised bed becomes incredibly rich and loaded with soil life. As the wood shrinks, it makes more tiny air pockets – so your hugelkultur becomes self tilling. The first few years, the composting process will slightly warm the soil giving a slightly longer growing season, in temperate and cold climates.
For more informations please visit http://www.richsoil.com/hugelkultur/ and http://permaculturenews.org/2012/01/04/hugelkultur-composting-whole-trees-with-ease/