In fact, without a good harrow, single-pass surface mixing would seldom be satisfactory. A minimum of a three-bar harrow is recommended. The method of attachment to an implement is very important in maintaining uniform incorporation. There should be at least two carrier arms per harrow section to maintain stability. The most aggressive mixing and tillage action is obtained with the tines perpendicular to the soil surface.
Aggressiveness decreases as the tines are angled toward the rear.
As tillage aggressiveness decreases, residue-shedding ability increases. Flexible-spike harrows also are used behind tillage implements. These harrows are usually suspended from the rear of the implement and penetrate soil under their own weight. A flexible-spike harrow typically consists of five bars of spike harrow teeth with about 1.5 inches of effective spike spacing. The narrow effective spacing results in considerable lateral soil movement.