The Nannen Arboretum is part of the Cornell University Cooperative Extension Home Grounds and Community Horticulture educational program. It is a non-profit, volunteered based organization dedicated to providing home garden and natural resource education, test plots for research, and an opportunity for nature appreciation and leisure.

In 1958, William O. Nannen, a local businessman, conservationist and political leader, donated land to build the new Cornell Cooperative Extension. The eight acre site was part of the Nannen farm and construction of the Extension building was completed in the spring of 1961. The Soil and Water Conservation Service constructed a pond on the site in 1965 to show agricultural people good pond construction and the benefits of having a farm pond. The pond is now known as Lake Nipponica.

In the spring of 1974, John Ploetz started working for Cornell Cooperative Extension as an aide in horticulture three days per week during the summer. His previous employer was the Davey Tree Expert Company of Ohio. As landscape and tree moving supervisor in the Northeast United States and Canada, John had vast experience with trees. The eight acres of land behind the Extension office were growing into weeds and brush, so John drew plans for what now is known as the Nannen Arboretum.

The name Nannen was given to the arboretum to recognize William and Sadie Nannen who not only donated the land, but were very instrumental in raising needed funds. They were honored by the planting of two Colorado Blue Spruce trees which were named for them.

It took a long time to get started. Dave Bruce, Director of the Cornell Cooperative Extension at that time, formed the first committee to manage the arboretum, and under his direction the arboretum became a reality.