Shallow Soils in the Garden

Shallow soils may best be deepened by digging only an inch deeper each year than the previous one  until a depth of 8" or 10" has been reached. Each  time an abundance of vegetable matter should also be  mixed with the soil-manure when available being  best. If dug too deeply in any one year, especially at the start, the poor subsoil will be in too great proportion at the surface and the plants will make a poor start or perhaps fail altogether.

Adapted from: : Gardening Short Cuts

See Also: Soil Sterilizing