Container-grown Shrubs Respond Differently to Controlled-release Fertilizer Rates in a Temperate Climate

Abstract

To determine the response of container-grown shrubs to controlled-release fertilizer (CRF) rate when grown in a temperate climate, Polyon® 19–04–10 + Minors, an 8–9 month CRF, was incorporated into growing substrates for ‘Gro-Low’ fragrant sumac (Rhus aromatica Aiton), ‘Goldmound’ spirea (Spiraea × bumalda Burv.) and ‘Bloomerang’® purple lilac (Syringa × ‘Penda’) transplants. Also, a 15–06–11 + Micros, a 10–12 month CRF, was incorporated into growing substrates for ‘Green Mound’ boxwood (Buxus × ‘Green Mound’), ‘Runyan’ yew (Taxus × media) and ‘Emerald’ white-cedar (arborvitae) (Thuja occidentalis L.) transplants, at six rates (0.15, 0.45, 0.75, 1.05, 1.35 and 1.65 kg·m−3 N; 0.25, 0.76, 1.26, 1.77, 2.28 and 2.78 lb·yd−3 N). We observed greater growth index, leaf area, and shoot dry weight at high vs. low CRF rates for the majority of species. Nutrient deficiency symptoms such as light green leaves were observed at low CRF rates for some species, including fragrant sumac, lilac and white-cedar. Optimal species-specific CRF application rates were 1.05 kg·m−3 N (1.77 lb·yd−3 N) for lilac and yew and 0.45 kg·m−3 N (0.76 lb·yd−3 N) for boxwood and white-cedar, while the optimal CRF ranges were 0.75 to 1.35 kg·m−3 N (1.26 to 2.28 lb·yd−3 N) for fragrant sumac and 0.75 to 1.05 kg·m−3 N (1.26 to 1.77 lb·yd−3 N) for spirea. Adjusting CRF application rates based on plant response may provide nursery growers with an efficient tool for managing nursery crop growth and production timing in the temperate climate.