Fertilizer Formulation and Method of Application Influence Bedding Plant Growth and Nitrogen Leaching in Urban Landscapes

Two experiments were conducted to evaluate fertilizer formulation, method of application, and frequency of application on growth of landscape bedding plants and nitrogen (N) leaching. In the first experiment, ‘Peppermint Cooler’ vinca (Catharanthus roseus (L.) G. Don ‘Peppermint Cooler’), ‘Bonanza Yellow’ marigold (Tagetes patula L. ‘Bonanza Yellow’), and ‘Hawaii Blue’ ageratum (Ageratum houstonianum Mill. ‘Hawaii Blue’) were planted in raised beds. Four inorganic fertilizer formulations used included 13N–5.6P–10.9K (13–13–13) and 15N–0P–12.6K (15–0–15) granular water soluble (GWS) fertilizers, Osmocote 14N–6.0P–11.6K (14–14–14) (3 to 4 month release) controlled-release fertilizer (CRF), and Osmocote 17N–3.0P–10.1K (17–7–12) (12 to 14 month release) CRF. Each fertilizer was applied at a rate of 4.9 g N/m² (1 lb N/1000 ft²) either incorporated into the top 10.2 cm (4 in) pre-plant or topdressed postplant. Additional treatments included an industry practice of incorporating 13N–5.6P–10.9K (13–13–13) pre-plant and topdressing 17N–3.0P–10.1K (17–7–12) post-plant; and a pre-plant incorporation of an organically-based fertilizer composed of recycled newspaper amended with chicken manure (caged layer manure). In Expt. 2, a similar experimental setup was used with ‘Peppermint Cooler’ vinca, ‘Red Vista’ salvia (Salvia splendens F. Sellow ex Roem. & Schult. ‘Red Vista’), and ‘Strata’ salvia (Salvia farinacea Benth. ‘Strata’). Inorganic fertilizers were applied in either single or multiple applications. Inorganic fertilizers included 15N–0P–12.6K (15–0–15) GWS fertilizer, Osmocote 14N–6.0P–11.6K (14–14–14) CRF, and Osmocote 17N–3.0P–10.1K (17–7–12) CRF. Three organically-based fertilizers were applied pre-plant and were composed of recycled newspaper amended with either chicken, beef cattle, or dairy cow animal manures. Summarizing across both experiments, plants treated with GWS fertilizers appeared to benefit with improved foliar color from immediate release of nutrients, while those treated with CRFs required at least 4 weeks to achieve dark foliar color. Nutrient leaching below plant roots was greater for GWS compared to CRFs. The industry practice treatment provided some improved plant growth in both experiments; however, it also caused initially high levels of soil-water-N (SWN) in Expt. 1. The organically-based fertilizer resulted in larger, more attractive (higher foliar color ratings) plants than inorganic fertilizers, though it also resulted in the highest levels of SWN compared to all other treatments.