The response of European chestnut (Castanea sativa Mill.) to varying Ca/Al ratios of 10, 1, 0.1, and control (no Al added) in nutrient solutions with constant concentrations of 1 mmol L⁻¹ Ca was investigated in a greenhouse experiment. The various Ca/Al ratios did not cause a significant effect on biomasses of roots, stems, shoots, and total plants. At a Ca/Al ratio of 0.1, however, a lower number of leaves with lengths >15 cm, a decreased biomass of leaves, an increased root/shoot ratio, and a decreased fine root ratio (roots with diameters <1 mm/root with diameters 1–2 mm) were observed. Elemental analyses of Al and base nutrient cations in roots and leaves revealed that increased Al concentrations reduced the uptake of Ca and Mg, but not the uptake of K. Aluminum concentrations were much higher in fine roots than in leaves, clearly indicating that only a minor amount of root Al was transported into leaves. This finding was supported by EDX analyses and microscopic data, where Al in fine roots was mainly detected in epidermal and cortical cells, but to a lesser extent in cells of the stele. The comparison of the results from the greenhouse experiment with field data from southern Switzerland suggests that there is no current risk originating from low Ca/Al ratio in the soil solution for European chestnut at the field site.