Home gardens are often the most agrobiodiverse sites in the anthropogenic environment, a space where crops and other useful plants are often transplanted from other components of the landscape. This study investigates the plant composition of home gardens and their usefulness in 12 small towns and villages—with three of these chosen as the focus for in-depth research—situated in the Jeju province of South Korea. The goal of the research is to explore their roles in local ethnobotany in the context of habitat conversion and land use change. The 131 home gardens surveyed in these villages yielded 164 species- and variety-level plant taxa (52 wild, 109 domesticated, and 3 introduced), of which 95 were useful plant taxa (39 wild, 55 domesticated, and 1 introduced). Use of home garden plants was predominantly for food and medicinal purposes. Home garden plant usefulness was more multi-functional and thus more versatile than practices associated with these plants in non-garden habitats. Plant diversity in home gardens was supported by the presence of nearby forest and grassland areas. Interview data indicate that plant users were motivated to transplant wild plants into their home gardens in order to secure a consistent supply, given decreases in wild plant populations in the last 15–20 years. The loss and overharvesting of forests and other wild plant habitats have caused the decrease in these plant populations. Underlying drivers of the habitat conversion and land use change influencing increased wild plant transplants to home gardens are local livelihood and lifestyle changes, including the earlier expansion of commercial agriculture beginning in the late 1960s and the accelerated growth of tourism since 2000.