These garden sites feature a Hügelkultur. Hügelkultur is the practice of mounding soil over materials which assist the soil in regenerating itself through increased water retention, the slow release of nutrients, habitat creation and complexity.
The process in general involves building a mound of woody material (typically rotting wood of varying diameters) and covering with layers of organic material (often referred to as ‘green manure’), compost, and top soil. While this practice has grown in popularity over recent years, it has been used in various forms by European cultures dating back many centuries.
Today Hügelkultur is being used in drier regions to retain water for growing crops and in challenging urban sites to regenerate soil and provide nutritious garden space for both perennial and annual food crops.
Visit individual sites for examples of Hügelkultur applications. A map of other Hügelkultur sites is available at: http://www.kingcd.org/pdf/hugelkultur-08.pdf