Effect of constant versus adjusted commercial fertilizer concentrations on poinsettia
Five poinsettia (Euphorbia pulcherrima Willd.), 'Freedom Red', 'Angelika Red', 'Nutcracker Red', 'Maren', and 'Red Splendor' received the following treatments of a commercial fertilizer based on nitrogen (N) concentrations off 75 mg L-1 to anthesis; 75 mg L-1 first 4 weeks then 125 mg L-1 to anthesis; 125 mg L-1 first 4 weeks then 200 mg L-1 to anthesis; and 200 mg L-1 to anthesis. Plants were fertigated to appearance of leachate from the bottom of the pot. Treatment concentrations greater than 125/200 and 200 mg·L-1 significantly increased plant width of 'Red Splendor', height of 'Nutcracker Red' and dry weight of 'Angelika Red', 'Nutcracker Red', and 'Maren'. Tissue concentrations of N, phosphorus (P), magnesium (Mg), and sulfur (S) increased as fertilizer treatment concentration increased for some cultivars. Significant differences between elemental concentrations of poinsettia cultivars occurred, specifically 'Nutcracker Red'. Although tissue nutrient concentrations were at or below the critical level, general observations of each cultivar indicated that all plants were of commercial quality and almost indistinguishable between treatments. Poinsettia stem strength was not significantly affected by any fertilizer treatment used in this study.