Validating Nitrogen Fertilization Recommendations for Florida Landscape Plants - Cool Season Annuals

The basis for current fertilizer recommendations for ornamental plants in Florida is unclear and limited and focuses on the needs of trees and shrubs. Trees and shrubs may have different nutritional requirements than do perennials, annuals, vines and groundcovers. Therefore, research needs to be done to validate the current fertilizer. Knowledge of specific nutrient requirements will allow plants to be zoned based on their fertilizer requirements. Fertilizer zoning will result in more efficient fertilizer application thus reducing nutrient losses to the environment. Plants were selected based on anecdotal evidence of high, moderate, and low fertilization needs for evaluation across a range of Nitrogen fertilization regimes. The plants were fertilized at five different N rates based on the FYN and FL Green Industries BMP manual recommendations for landscape fertilization: 0.0 g N·m^-2·yr^-1, 9.8 g N·m^-2·yr^-1, 19.6 g N·m^-2·yr^-1, 29.4 g N·m^-2·yr^-1, and 58.8 g N·m^-2·yr^-1 (2, 4, 6, and 12 lbs N·1000ft^-2·yr^-1). Nitrogen fertilization responses were determined for the following cool season bedding plants: Antirrhinum ‘Montego Yellow’, Dianthus ‘Telstar Crimson’, and Viola ‘Delta Pure Violet’. Each of the five treatment beds were replicated three times. Every bed contained three replication groups of each species. Data collected was: plant growth measurements, aesthetic quality ratings (1-5), chlorophyll measurements (using a SPAD meter to measure chlorophyll content), and shoot dry mass. Plant measurements and fertilizer applications occurred in six-week intervals. Plots were 10 feet by 40 feet raised beds filled with soil with little nutrient content. Drip Irrigation was used. No mulch was added to beds in order to minimize outside nitrogen contributions. Results indicate that N requirements differ among species and were within the range recommended by Green Industries BMPs and FYN. The N rates for Antirrhinum, Dianthus, and Viola suggested in this study were determined for optimal growth and quality and are more specific than the existing recommendations.