We applied combustion ash from a woody biomass power generator to a young hinoki cypress plantation (Chamaecyparis obtusa, 1 kg of ash per tree per year) in the southwestern part of Shikoku Island, Japan, and we monitored the annual diameter and height growth for two years. Linear mixed-effects models indicated that the ash application decreased annual increment of stem diameter and tree height, and the two-year serial ash application lowered the annual tree growth more than the single-year ash application. The results of the laboratory leaching test suggested that a high concentration of K⁺, SO₄^2‒, and Cl^‒ was leached from the combustion ash during the first rainfall, and the highly concentrated eluate might effect on the growth of the young hinoki cypress. The ash application to conifer plantations should be considered to determine the ash amount that influences tree growth and the use of the scattering technique.