After retirement, he contributed to the taxonomy of the Agaricomycotina, particularly the tooth fungi of the families Hydnaceae and Bankeraceae, in which he described several new species.
[2] His early research concerned the fungal infestation of plants, such as that of Colletotrichum lindemuthianum on beans (Phaseolus).
Working with John Frederick DeWitt Hockey, they made many contributions to the control and prevention of diseases of horticultural crops.
Collections forays throughout Nova Scotia, in the Great Smoky Mountains, New Mexico, the Upper Peninsula of Michigan, and the Pacific Northwest led to him describing several new species in the genera Steccherinum, and tooth fungi in Hydnellum, Sarcodon, Phellodon.
[1] The tooth fungus Sarcodon harrisonii was named in his honor by Richard Baird, who noted "Dr. Kenneth Harrison the North American expert on the stipitate hydnums.