Propagation - A 70°F minimum night temperature is a must. Sterilize pots, benches, flats, and knives before taking cuttings. As cut tings begin to root, reduce the amount of mist (this is extremely important with poinsettias). Fertilize the cuttings as soon as roots form (even under the mistt . Fertilization- Poinsettias require relatively high applications of nitrate nitrogen and potassium. We would recommend 300 ppm N and K at each watering. Be sure to use a high nitrate to ammonia nitrogen formulation Your fertilizer should also contain a phosphorus source. If you are using phosphoric acid for pH control, that addition will supply adequate phosphorus. We do not recommend calcium nitrate in Indiana because it just adds to your pH problem. Add an Epsom salt (1 lb./100 gal. water) drench every 4 to 6 weeks to supply magnesium. Do not add to your normal fertilizer solution. Several have asked about molybdenum additions. I personally feel that the "peat-lite special" fertilizers or a soluble trace element mix has adequate molybdenum. However, it will not cause harm to add additional molybd num at the rate of 0.1 ppm.
Source: • Floriculture Indiana Volume 3. No. 4
Keywords: PH Pinching ammonium or sodium molybdate Calcium nitrate