Growth of New Guinea Impatiens Inhibited by High Growth-medium Electrical Conductivity

To test the effects of fertilizer concentration and growth medium electrical conductivity (EC) on the growth of New Guinea impatiens (Impatiens sp. hybrids or I. platypetala Lindl.), plants of `Selenia' were grown 70 days in a commercial soilless medium and irrigated with solutions of 20N-4.3P-16.6K at concentrations of 0.5, 1.0, 1.5, or 2.0 g·liter -1 . In a fifth treatment (“delay”), no fertilizer was applied for the first 14 days after planting, then 0.5 g·liter -1 was applied for the next 14 days, followed by 1.0 g·liter -1 until the end of the experiment. Measurements of shoot dry weight and growth medium EC were made at 14-day intervals. Differences in dry weight between fertilizer treatments became significant (P = 0.0001) 42 days after planting. Over the 70-day experiment, plants grew most with 0.5 g·liter -1 and delay treatments. High fertilizer concentrations (1.5 and 2.0 g·liter -1 ) caused the most growth suppression and resulted in increasing growth medium EC with time. An EC of ≈1.5 dS·m -1 or higher was associated with suppressed growth beginning 42 days after planting. A mild chlorosis developed on the leaves of some plants at the two highest fertilizer concentrations.