New York State Flower Industries , Inc
Poinsettia nutritional requirements are similar to most floricultural crops. The need for large amounts of nitrogen has been shown by many researchers. This nitrogen has been supplied in various fertilizer forms. Among these ammonium nitrate, ammonium sulfate, potassium nitrate and calcium nitrate along with various commercial formulations of 20-20-20 and other analyses have all been recommended. Because poinsettias have certain root rot problems, the recommendations for a growing medium have been to provide one that has good drainage, good aeration, holds nutrients and has a pH around 5.0-5.5. This last recommendation is made on the basis that Thielaviopsis basciola, one of the root rot diseases, does not grow well at a low pH. Therefore, by keeping the growing medium on the acid side, some biological control of Thielaviopsis has been obtained. The choice of ammonium sulfate as a fertilizer would be a logical one in that it has an acid reaction in the soil and would help to keep the pH on the acid side and thus control Thielaviopsis. Since the ammonium must be converted to nitrates for plant use through the process called nitrification some consideration was given as to factors affecting this conversion. Temperature plays a large role in the nitrification process, the warmer the temperature the more rapid the process proceeds. Because poinsettias are grown at minimum night temperatures of 62°F and some of the newer cultivars are grown at a minimum 65CF, there should be no problems due to slow conversion of ammonium to nitrate nitrogen.
Keywords: Thielaviopsis basciola Root rot diseases acid side biological control Nitrification