Hollis Koster grew up at the famous Hermann Hotel with seven other siblings. The Hotel supported an early 19th century glasstown along the Mullica. Koster's family came from Germany to manage the Hotel. After graduating from Rensselaer Polytechnic Institute in 1934, Koster threw himself into the wildlife of South Jersey. He spent many days in tall boots, walking through patches of local ferns, bushes, and wildflowers. He made a personal label entitled, "PLANTS OF SOUTHERN NEW JERSEY," to help him organize his findings.

Koster's hobby even led him into a small business enterprise. He originally contacted pharmaceutical firms to further develop his collection. Eventually a loose partnership was formed, and he collected medicinal plants and sold them to these firms.

Koster also extended his hobby into an invitation to make international friends. He began a plant exchange with Otto Behr in Germany. After learning German in order to communicate with Behr, Koster and his penpal exchanged letters and specimens, even while the threat of war in Europe loomed. Communication between the two eventually slowed, and finally ended due to the start of World War II.

Known throughout Green Bank for his avid and unique understanding of botany and glassworks, Koster later decreased his botantical activities. However, he still enjoyed outings in the Barrens and walks around his Mullica home.

Koster passed  away in 1966. His brother, Glendin, donated a large number of his books to the Glassboro Library. Some of Koster's collection can be found in the Batsto Nature Center and the Herbarium of the Academy of Natural Sciences in Philadelphia.