Growth response of herbaceous ornamentals to phosphorus fertilization

A series of experiments investigated the effects of increasing phosphate–phosphorus (P) concentrations on the growth and development of four horticultural species.

In experiment 1, petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter] plants were grown using eight P concentrations, and researchers found that the upper bound for plant growth was at 8.72–9.08 mg·L⁻¹ P, whereas concentrations ≤2.5 mg·L⁻¹ P caused P deficiency symptoms.

Experiment 2 investigated P growth response in two cultivars each of New Guinea impatiens (Impatiens hawkeri W. Bull) and vinca [Catharanthus roseus (L.) G. Don]. Growth for these plants was maximized with 6.43–12.42 mg·L⁻¹ P. In experiment 3, ornamental peppers (Capsicum annuum L. ‘Tango Red’) were given an initial concentration of P for 6 weeks and then switched to 0 mg·L⁻¹ P to observe whether plants could be supplied with sufficient levels of P, and finished without P to keep them compact.

Plants switched to restricted P began developing P deficiency symptoms within 3 weeks; however, restricting P successfully limited plant growth. These experiments indicated that current P fertilization regimens exceed the P requirements of these bedding plants, and depending on species, concentrations of 5–15 mg·L⁻¹ P maximize growth.

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