The challenges of fertilizing poinsettias

Poinsettias are a beautiful crop grown for the Christmas season. It is a longer crop than most grown in the greenhouse, so it can come with additional challenges. One of these challenges is fertilization. Below are guidelines on the important elements that poinsettias need as well as application rates depending on the stage of plant development.

Selecting the proper fertilizer
Before selecting fertilizer(s) for your poinsettia crop, test the water. The fertilizer program should consider the alkalinity of the water as it has a major influence on the growing medium's pH. If the alkalinity is high, then acid needs to be injected into the water to bring it down to acceptable levels to minimize high pH problems in the growing medium.

A water test also measures the quantity of beneficial nutrients in water, such as calcium, magnesium and sulfate, which dictates the need for supplemental fertilizers to provide these elements. Water can also supply problematic amounts of sodium, chloride or fluoride that may dictate leaching frequency.

Experts also suggest using fertilizers with higher levels of nitrate to grow a tone plant vs. higher ratios of ammonium that can cause stretching. Remember that higher levels of phosphorus (more than 30 ppm P) have been found to cause more stretching than ammonium. Be cautious as fertilizers with higher ratios of nitrate vs. ammonium are usually “potentially basic” and will cause the pH of the growing medium to rise. If higher nitrate fertilizers are used, then more acid may need to be injected into the water to offset potential increases in growing medium pH.

Read more at PRO-MIX