The loss of soil biodiversity through agricultural intensification is a major contributor to the collapse of ecosystem services. Despite their wide application to promote biodiversity, the impact of flower strips on soil organisms is largely unknown. Here, we studied the effects of perennial flower strips on earthworm communities at 46 sites with paired croplands and perennial flower strips. Earthworm population densities in flower strips were on average 231% greater than in adjacent croplands. Flower strips can enable the establishment of anecic and epigeic populations at sites at which they are absent in croplands. Furthermore, flower strips likely serve as a habitat for the reproduction of endogeic earthworms. We expect that the promotion of earthworms through flower strips improves soil functions and benefits higher trophic taxa. We propose that optimized seed mixtures, improved spatial configuration, and establishment of temporal continuity of flower strips can further promote soil ecosystem services.