Double digging

Double digging is a gardening technique used to increase soil drainage and aeration. It involves the loosening of two layers of soil, and the addition of organic matter.
Double digging is typically done when cultivating soil in a new garden, or when deep top-soil is required. On poor or heavy soils, or for vegetable gardens, double digging might be required every 3–5 years. In other cases, double digging is only really needed on starting a new garden, or on total replanting.