Poinsettias require medium to high fertility levels between 150 and 300 ppm N, with the rate adjusted to take into account plant vigor. Optimal substrate pH values for poinsettia range from 5.5 to 6.5. If the substrate pH drifts lower than 5.5, plants will become stunted and color delayed. Substrate pH values above 6.5 inhibit Fe availability and induce interveinal chlorosis and stunted plant growth.
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