Double digging is a useful way of cultivating soil in new gardens and in situations where deep topsoil is required. Ordinary digging is good enough for most circumstances.
Choose double digging over other methods of soil cultivation where the soil is compacted, where ground has not been previously cultivated, where demanding long-term plants such as asparagus are planned or when making raised beds. All bare ground is suitable for double digging.
It is not necessary to double dig every year, but on poor or heavy soils and in vegetable gardens it may be needed every three to five years. Otherwise borders only need double digging at their creation and on total replanting.