This paper describes the activities of amateur plant breeders and their application of various methods and technologies derived from genetics research over the course of the twentieth century. These ranged from selection and hybridization to more interventionist approaches such as radiation treatment to induce genetic mutations and chemical manipulation of chromosomes. I argue that these activities share characteristics with twenty-first-century do-it-yourself (DIY) biology (a recent upswing in amateur experimental biology) as well as other amateur science and technology of the twentieth (...) century. The characterization of amateur plant breeding as amateur experimental biology offers a corrective to a dominant narrative within the history of biology, in which the turn to experimental research in the early twentieth century is thought to have served as an obvious dividing line between amateur and professional activities. Considered alongside other better-known amateur efforts, it also suggests that we might gain something by taking a more unified approach to the study of amateur science and technology. (shrink)