After the war, Groenland moved to Paris to work as an assistant to Louis de Vilmorin, a French biologist and horticulturist who was also a member of the family firm Vilmorin-Andrieux.
He was a founding member of the Société botanique de France and was known for his work creating hybrids by crossing Triticum vulgare with various species of Aegilops.
[3] His botanical research also focused on liverworts, seagrasses, and the genus Drosera; and he served as the editor of the journal Revue horticole.
[1][2] In addition to his research and writing, Groenland developed skills in preparing botanical slides while living in Paris.
He ran his own microscopist business from his residence at 13 Rue des Boulangers, and along with Marie Maxime Cornu and Gabriel Rivet, he wrote Des préparations microscopiques tirées du regne végétal, which was commonly used in the 19th century as a textbook on the preparation of microscope slides.