Growth of ornamental plants irrigated with nutrient or polyethylene glycol solutions of different osmotic potentials

Summary Six ornamental species (Petunia hybrida, Callistephus hortensis, Coleus blumei, Celosia pyramidalis, Antirrhinum majus andTagetes erecta) were grown in solutions containing high concentrations of polyethylene glycol (MW 4000) or of Nitrogen: Phosphorus: Potassium. At equal osmotic potentials, top dry weight, leaf area and leaf elongation rate were all reduced more by polyethylene glycol than by NPK. Polyethylene glycol also produced some leaf damage which did not occur with NPK solutions. Osmotic potentials of –600 kPa due to NPK reduced growth of the six species by at least 25% compared with growth of control plants (at –20 kPa). Tolerance ranking to high fertilizer in the irrigation solution increased from Snapdragon (most sensitive), Marigold Coleus, Aster, Celosia and Petunia (most tolerant).