Ectomycorrhizal (ECM) fungi are key players in N cycling in coniferous forests, and forest management such as application of wood ash can affect their functionality. The aim of this study was to determine the effects of wood ash application on ECM fungal mycelial production, capacity to retain N, diversity and community composition. In-growth mesh bags were installed in control and treated plots. After 6 months, ¹⁵N labeled ammonium and nitrate were applied into the mesh bags, and 24 h later extramatrical mycelium (EMM) was extracted and analyzed. Wood ash had no effects on EMM in-growth, N retention capacity, diversity or community composition. In contrast, there were significant seasonal differences in the amount of EMM produced. These results demonstrate that applying up to 6 t ha⁻¹ of wood ash in this type of plantation forest is a safe management practice that does not increase N leaching or negatively affect ECM fungi.