Background Climate change is expected to drive trailing-edge range redistributions of arctic-alpine plant populations, bringing together immigrant plant ecotypes and soil microbial communities associated with already resident ecotypes. Aims The goal of the present study was to assess growth performance and plant–microbe interactions between seedlings and native and foreign microbial communities in ecotypes of the cushion plant Silene acaulis from Europe and North America. Methods Using seed sourced from Colorado, USA, and Ireland we grew Silene seedlings in sterile bulk soil with live inocula added from their own local soil and each other’s soil. We measured above-ground plant growth metrics, and analysed fungal and bacterial community composition using marker gene sequencing and microscopy. Results Seedlings growing in foreign soil inocula showed significantly greater biomass or shoot length compared to growth in home soil inocula. While seedling root microbiomes were overall convergent with each other compared to source soil inocula, significantly lower filtering of fungal taxa from the soil was observed for seedlings growing in foreign compared to home soil inocula. Conclusions Foreign plant ecotypes from distant habitats may experience competitively beneficial effects when growing in local soil communities; however, the nature and generality of these interactions requires further analysis.