Born in San Francisco, California, Sessions’ interest in science and horticulture developed at a young age. She spent several months traveling in the Sandwich Islands (now Hawaii) after graduating from high school. In 1881 she became the first woman to graduate with a B.S. from the University of California, Berkeley, where she studied chemistry.
In 1885 Sessions opened her first nursery in San Diego, moving the business several times as the city expanded. For a time, she leased a portion of the still-developing City Park (now Balboa Park) in exchange for donating hundreds of trees to the City. She was given the title City Gardener, and her work with the park earned her the nickname the “Mother of Balboa Park.” Along with San Diego philanthropist George Marston, she was instrumental in the formation of the City’s Park Improvement Committee.
Sessions published articles in magazines, newspapers, and journals, including California Garden. She also taught extensively throughout her career and was a founding member of the San Diego Floral Association. She was responsible for the introduction of a large variety of plants to Southern California and the popularization of the Queen Palm as a street tree. Sessions was the first woman awarded the American Genetic Association’s Frank M. Meyer Medal.