Karen Helene Madsen was born on October 13, 1942, on a farm between Avoca and Shelby, Iowa, with a country doctor and her father in attendance. She was the daughter of Danish immigrants, Oga and Ella Madsen.

With her three older sisters, Karen thrived in the country and loved life on the farm. She began school at the one-room country schoolhouse near her birthplace, but when the family moved closer to Shelby she attended Shelby Consolidated School, where she played on the basketball team and became an accomplished trombone player in the school band.

Karen followed her sister Mary Jane to the University of Iowa, graduating with a degree in English in 1964. From there, she moved to the East Coast and began a career as an editor of English textbooks, including a set of literature texts for grades 7 through 12. From 1992 until her retirement in 2007 she was the editor of Arnoldia, the quarterly horticultural journal of Harvard University's Arnold Arboretum.

After two previous marriages, Karen met her life's companion, John Furlong, in 1987, when he was the director of the Landscape Institute at Harvard University and she took classes there. In 1996 they purchased a home in Marshfield, Massachusetts, south of Boston, near the Atlantic shore. It was situated on two acres overlooking a marsh that had originally been Daniel Webster's cranberry bog, adjacent to woods belonging to the town of Marshfield. It was there that Karen was able once again to indulge the passion for plants that had lain dormant ever since she left the farm, and she spent many happy hours developing her garden, walking the property, feeding the many birds that lived there, and taking care of her beloved cat, Chloe.

Always an avid learner, she continued to educate herself with extensive reading and research about plant materials and landscape design history—writing articles, developing a course in history for the Landscape Institute, and becoming an expert at identifying trees. She and John traveled extensively with colleagues in the landscape field, including to China, Japan, Finland, Turkey, and a variety of locales in the U.S. Over the years, Karen also enjoyed frequent visits to her many relatives in Denmark.

In 2018, Karen's health required a move to the Wingate at Silver Lake Nursing Home in Kingston, MA, and it was there that she died of complications from Alzheimer's disease on October 22, 2022. Karen was predeceased by her parents, her sister Mitzi Madsen Fox, her daughter Holly Madsen, two nephews, and a niece. She is survived by her husband, John Furlong; her sisters, Margit Paulsen of Council Bluffs, IA, and Mary Jane Kaplan of New York City; three stepdaughters—Signe Kurian, Molly Brewster, and Leah DiRamio; and many nieces, nephews, great-nieces and -nephews, and great-great-nieces and -nephews.

The dates and venues of memorial services to be held in Iowa and Massachusetts will be announced later. Please check back for updates.