Recycling of peat ash back to cut-away peatland areas for growing short-rotation willows was studied in a field experiment in central Finland. Application amounts of 10, 160, 320 and 640 t/ha were tested. Willow (S. x dasyclados) planted as cuttings was grown with one-year rotations for four years. The effect of additional fertilization (O, N, P, K, NP, NK, PK, NPK) was also tested. Biomass production, soil and foliar nutrient concentrations were measured. High ash application amounts increased the soil extractable P, K, Ca, Mg and Fe concentrations manyfold compared with the 10 t/ha treatment. Marked increases were also noted in soil pH, electrical conductivity and microbial activity. At the 10 t/ha treatment foliar K concentrations were low and higher applications of ash or additional K fertilization increased foliar K concentrations. The effect of potassium fertilization on foliar K concentrations decreased with increasing amounts of ash used. Biomass production was low at the 10 t/ha treatment and increased manyfold with higher application amounts. However, additional potassium fertilization was necessary unless extremely high application amounts were used. Even the highest application amount of peat ash (640 t/ha) was not toxic to the willow.