ABSTRACT Ash dieback, induced by Hymenoscyphus fraxineus , a pathogenic ascomycete native to East Asia, has severely affected ash stands in Europe, raising questions about the future of the species. Reports on the relationship between host density and disease incidence are contradictory. Although the most recent studies indicate a reduction in disease severity at lower host densities, the evidence remains largely correlative, with the only study experimentally manipulating host density concluding that no effect of host density on ash dieback can be demonstrated. We investigated the impact of host density and tree species mix on the evolution of ash dieback and subsequent radial growth of affected trees. Data were extracted from a network of permanent thinning trials comprising pure and mixed stands of even‐aged ash and a progeny trial where ash dieback was monitored from 2010 to 2015 (39 plots at seven sites). We showed that host density, estimated from ash basal area, has a significant impact on the evolution of ash dieback and subsequent growth of affected stands. Large ash trees at low densities suffered little from the disease. The impact on ash growth is mainly due to the reduction in disease severity, although a significant effect of tree species mixing on ash growth also occurs for healthy trees. As ash trees are often present at low densities in mixtures, this should mitigate ash dieback.