Nutritional factsheet New Guinea impatiens

New Guinea impatiens require low fertility of 100 to 150 ppm N. They prefer a pH within the range of 5.8 to 6.2. This range prevents low substrate pH induced iron (Fe) and manganese toxicities which occurs if the pH drifts lower than 5.5. Substrate pH values above 6.5 can also inhibit Fe availability and result in the upper foliage developing interveinal chlorosis (yellowing).

New Guinea impatiens should be grown with a pH range of 5.8 to 6.2. Use recommended 1:2 Extraction, SME, or PourThru methods to determine and monitor substrate pH and soluble salts [referred to as electrical conductivity (EC)] values. Additionally, conduct routine foliar analysis tests to monitor crop nutrient status. Monitoring substrate pH and nutrient status will enable growers to avoid pH induced nutritional disorders.

Substrate pH below 5.8 causes increased uptake of iron (Fe) and manganese (Mn) to toxic levels which will accumulate in leaf tissue. Plants exhibiting Fe and/or Mn toxicity will exhibit lower leaf chlorosis and black spotting or speckling along the leaf margin progressing into the leaf. Other symptoms may include stunting and twisting or malformations of the new growth (Dole and Wilkin, 2005; Gibson et al., 2007). Corrective procedures for low substrate pH should begin within the range of 5.5 to 5.8.

High substrate pH above 6.5 can inhibit Fe uptake causing newly developed leaves to become deficient in Fe and exhibit interveinal chlorosis. If plants become severely Fe-deficient, interveinal chlorosis intensifies and leaves become white. The symptoms then progress to mature leaves where the petioles and stem will exhibit a light-pink coloration, necrotic (dead tissue) patches develop along the leaf midrib, and pedicles, sepals, and flower buds develop a faded green-yellow color (Gibson et al. 2007). Corrective procedures for high substrate pH should begin within the range of 6.2 to 6.4.

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