For Poinsettia production, start with a well-aerated media at an EC of 1 – 1.5 mS and starting pH of 5.2 – 5.5. Attention should be paid to maintaining temperature at optimum levels for good growth – leaf unfolding increases between 10° C and 25° C, then declines above 25° C. Flower quality (optimum bract size) is achieved at 20° C for the first 3 – 4 weeks after color has begun showing and then a temperature of 15° C will develop color and prevent cyathia drop.
Begin fertilizing rooted cuttings with 150 – 200 ppm Nitrogen (N) from Plant-Prod® Solutions 17-5-17 Complete or Plant-Prod Solutions 19-8-13 Total Plus or Plant-Prod 18-6-20 Poinsettia Plus. A constant feed of 200 – 250 ppm N is appropriate for good quality. Maintain media EC at less than 1.2 mS and pH at 5.8 – 6.2, using saturated media extract (SME).
Calcium (Ca) nutrition is also important to reduce bract edge burn. Maintain proper levels using Plant-Prod 15-0-15 Cal Plus which can be alternated with Plant-Prod 18-6-20 Poinsettia Plus depending on water analysis or using Plant-Prod Solutions 17-5-17 Complete.
Foliar Ca sprays might be necessary if temperature and humidity conditions are uncontrollable. Calcium chloride, reagent grade, is recommended at 200 – 400 ppm Ca, weekly, from first color until pollen is shed to prevent bract edge burn.
Magnesium (Mg) is supplied at high levels in Plant-Prod 18-6-20 Poinsettia Plus (35 ppm Mg at 200 – 250 ppm N) and depending upon water and media levels this may be adequate. If not, then Plant-Prod 12-2-14 Optimum with 6% Ca and 3% Mg may be used instead of Plant-Prod 15-0-15 Cal Plus for alternating with the main fertilizer.
Molybdenum (Mo) nutrition is very important to Poinsettia growth. Plant-Prod 18-6-20 Poinsettia Plus provides 1 ppm Mo at 200 – 250 ppm N, which ensures that no deficiency will occur. Foliar Mo levels should be maintained between 1-5 ppm. A corrective drench of 50 ppm Mo from Sodium Molybdate (0.1 g/L) can be used if levels fall below 1 ppm in the tissue. Once symptoms of downward curling are seen on the middle-aged leaves it is too late to correct the problem.
Fertilizer should be reduced drastically in the 2-3 weeks prior to shipping in order to harden off plants. Plant-Prod Solutions 15-0-20 No-Stretch®, Plant-Prod 18-6-20 Poinsettia Plus, Plant-Prod 15-0-15 Cal Plus or Plant-Prod 12-0-44 Finisher at 50-100 ppm N is appropriate once a week.