Soil Information for Home Gardens
Shallow Soils in the GardenShallow 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