In the past decade, various studies have described the effects of microbial volatiles on other (micro)organisms in vitro , but their broad-spectrum activity in vivo and the mechanisms underlying volatile-mediated plant growth promotion have not been addressed in detail. Here, we revealed that volatiles from root-associated bacteria of the genus Microbacterium can enhance the growth of different plant species and can prime plants for growth promotion without direct and prolonged contact between the bacterium and the plant. Collectively, these results provide new opportunities for sustainable agriculture and horticulture by exposing roots of plants only briefly to a specific blend of microbial volatile compounds prior to transplantation of the seedlings to the greenhouse or field. This strategy has no need for large-scale introduction or root colonization and survival of the microbial inoculant.