Application of granular materials is an important part of most turfgrass maintenance programs, but is not often studied by horticulturists. Agricultural engineers have conducted many research studies over the past 50 years on the theory, testing, and use of granular applicators. Understanding the theory of granular distribution can aid horticulturists and turfgrass professionals in the effective use of spreaders. This article will review relevant engineering studies and interpret some of the results to provide help in using spreaders more effectively. Proper operating mode, proper pattern adjustment, and the use of an appropriate swath width can greatly improve pattern uniformity. For instance, a half-width pattern has been proven more effective at pattern improvement than right-angle patterns, and the detrimental effect of humidity on spreader pattern has been demonstrated.