We performed a field assay to assess the efficacy of strains of actinobacteria belonging to the Streptomyces genus, isolated from two Mediterranean semiarid sites (Rellano and Calblanque) with different soil characteristics, with regard to the establishment of Rhamnus lycioides L. seedlings in both locations, as well as their effect on soil chemical and microbiological properties 1 year after planting. At the Calblanque site, the inoculation with native strains was more effective than that with allochthonous strains, with respect to increasing shoot dry weight (about 48 and 28 %, respectively, compared to control plants), primarily due to improvements in NPK uptake and plant drought tolerance. However, at Rellano, the efficacy of plant growth promotion was not influenced by the strain origin. The highest increases in the urease, protease, and dehydrogenase activities and in microbial biomass C in response to inoculation with actinobacteria occurred at the Rellano site (about 200, 28, 29, and 30 %, respectively, compared to the respective controls), regardless of the origin of the strain assayed. Strain origin and the biological fertility of the plantation site should be considered in the selection of strains of actinobacteria for use in the revegetation with shrub species in semiarid environments.