Effect of constant versus adjusted commercial fertilizer concentrations onpoinsettia

Five poinsettia (Euphorbia pulcherrima Willd.), 'Freedom Red', 'Angelika Re d', 'Nutcracker Red', 'Maren', and 'Red Splendor' received the following tr eatments of a commercial fertilizer based on nitrogen (N) concentrations of : 75 mg L-1 to anthesis; 75 mg L-1 first 4 weeks then 125 mg L-1 to anthesi s; 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 si gnificantly 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) increa sed as fertilizer treatment concentration increased for some cultivars. Sig nificant differences between elemental concentrations of poinsettia cultiva rs occurred, specifically 'Nutcracker Red'. Although tissue nutrient concen trations were at or below the critical level, general observations of each cultivar indicated that all plants were of commercial quality and almost in distinguishable between treatments. Poinsettia stem strength was not signif icantly affected by any fertilizer treatment used in this study.