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Photo: © Thomas Leo Ogren
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.
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