Responses of Six Species ofProteaceae, in Containers, to Controlled‐Release Fertilizer

Seedlings of Adenanthos sericeus, Banksia ericifolia, Banksia hookeriana, Conospermum caeruleum, Protea cv. Masquerade, and Leucadendron cv. Sundance were grown in a soilless potting medium containing controlled‐release Osmocote® fertilizer (17:1.6:8.7) at eight treatment levels: 0, 1.25, 2.5, 3.75, 5.0, 6.25, 12.5, and 18.75 kg m−3. After 6 months, shoot dry mass and the concentrations of nitrogen (N), phosphorus (P), and potassium (K) in recently matured leaves were determined. At the lowest rate of applied fertilizer, growth was stunted for all species. Maximum shoot dry mass was associated with a fertilizer rate of 2.0 kg m−3 for L. cv. Sundance, 2.5 kg m−3 for C. caeruleum and B. ericifolia, and 3.75 kg m−3 for P. cv. Masquerade, B. hookeriana, and A. sericeus. At the highest fertilizer rate, for all species except A. sericeus, plants displayed foliar symptoms typical of fertilizer excess, and growth was reduced. A range of concentrations of N, P, and K in leaves at optimum growth was determ...