He specializes in nursery management and teaches undergraduate and graduate courses in nursery production and pesticide use. Gillman earned his doctorate in horticulture and a master's degree in entomology from the University of Georgia. He has published research papers on topics as varied as how silicon affects plant resistance to disease and how lime affects plant growth. He has also done extensive research on organic pesticides. When not teaching or conducting research, Gillman participates in numerous master gardener programs in Minnesota and nearby states.