Frost embarked on a European tour in 1912 and was greatly influenced by his encounters with Italian and English gardens. Upon returning to the United States, Frost also spent time viewing the southern plantations along the Ashley River, including the Magnolia Plantation in Charleston, South Carolina.
In 1914, Frost opened an office in Harvard Square where he transitioned away from his early interests in suburban subdivisions and garden city planning and eventually specialized in designing gardens throughout
Highly knowledgeable about plants, he was a lifelong member of the Massachusetts Horticultural Society and would frequently lecture at the Rhode Island School of Design and the Cambridge School of Architecture and Landscape Architecture. Paul Frost died in Boston on June 21, 1957.