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- Author or Editor: H.T. Kraus x
A series of experiments were undertaken to determine the effects of nitrogen (N), phosphorus (P), and potassium (K) concentrations and N:P:K ratio on flowering and vegetative growth of two herbaceous perennials, Hibiscus moscheutos L. (hibiscus) and Rudbeckia fulgida var. sullivantii Ait. ‘Goldsturm’ (rudbeckia). Plant growth and flowering of both hibiscus and rudbeckia were influenced by concentration and ratio of N, P, and K. When N was held constant at 100 mg·L−1, 4:1 N:K (25 mg·L−1 K) and 16:1 N:P (6.3 mg·L−1 P) were optimal for growing hibiscus, whereas higher K concentration (1:2 N:K, 200 mg·L−1 K) and lower P concentration (32:1 N:P, 3.1 mg·L−1 N) were required for optimal growth of rudbeckia. However, when holding N constant at 100 mg·L−1 and varying both P and K in the fertilizer solutions, higher P and K concentrations and a 2:1:2 (50 mg·L−1 P, 100 mg·L−1 K) N:P:K ratio best supported hibiscus growth, whereas 3:1:2 (33 mg·L−1 P, 66 mg·L−1 K) N:P:K was needed for growth of rudbeckia. Finally, when both N concentration and N:P:K ratio were altered, optimum growth of both hibiscus and rudbeckia was achieved at similar and lower P and K concentrations (25 mg·L−1 P and 50 mg·L−1 K) and 200 mg·L−1 N. An 8:1:2 N:P:K ratio was optimum for production of both hibiscus and rudbeckia, although 12:1:2 N:P:K (200 mg·L−1 N, 17 mg·L−1 P, 33 mg·L−1 K) produced similar growth of rudbeckia. Based on results of these two herbaceous perennials, it appears herbaceous perennials have N requirements similar to annual plants and P and K requirements similar to woody plants. Furthermore, the two herbaceous perennials used in this study required nutrients in the fertilizer solution at a higher N:P:K ratio than either annual or woody plants. Foliar concentrations of 2.2% N, 0.4% P, and 1.9% K were adequate for growth of hibiscus, whereas 2.4% N, 0.2% P, and 2.6% K were required to maximize growth of rudbeckia.