This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This is an excellent cultural operation, and is almost equal in value to double digging. By digging a piece of ground lengthways, the soil from the trench is placed on the adjoining soil to the right or left, thus forming a ridge about 2 ft. high on one side and a trench correspondingly deep on the other. If the base of the ridge be 2 ft. wide, soil to cover one-half of it is taken from one side, and to cover the other half from the other side. In this way heavy soil is brought up, and a large surface is exposed to the weather. The soil in the bottom of the trenches on each side of the ridges may be still further improved by breaking up with the fork. A modification of ridging is to turn up a "spit" of soil and invert it in same place. The next spit is taken up and placed on top of the first, thus making a hillock and hollow alternately. Soil that has been ridged up in winter will be beautifully sweet and mellow in spring, when the crests of the ridges may be easily levelled down with a fork before sowing or planting operations.