In 1898, he began doctoral studies at Columbia University, focusing on fungi and publishing on such agriculturally important fungal diseases as powdery mildew, ergots, and smuts.
[4] In this period, the fencing-in of the west over the previous half century had pushed sheep and cattle onto ever-smaller areas of rangeland, resulting in overstocking that had damaged the land.
[4] In the course of his researches, Griffiths became especially interested in plants adapted to low-water environments such as prickly pear cactus that could be used as supplemental or emergency feed for livestock.
[1][5] As a result of his investigations into the cultivation potential of these kinds of food sources, he became an authority an cacti, assembling a collection of well over 3000 members of the cactus genus Opuntia.
[1][2] In his final two decades, Griffiths focused on bulbous plants both native and imported, becoming a senior horticulturalist for USDA's research on bulb production.