About The Author
THOMAS LEO OGREN has a master’s degree in agricultural science and is the creator of the Ogren Plant Allergy Scale (OPALS), a plant-allergy ranking system now used by the United States Department of Agriculture. He is a horticulturist and allergy researcher as well as a former landscape gardening instructor, nursery owner, and gardening radio show host. He lives in San Luis Obispo, California.
