Abstract A hypothesis was tested that the cause of a damaging marginal bract necrosis common to ‘Gutbier V-14 Glory’ poinsettia is a deficiency of Ca that is expressed when the rapidly growing bract outdistances the current supply of Ca. Plants were grown in the greenhouse in a sedge peat-EauGallie sand mix with fertility adjustments designed to moderately enhance Ca deficiency. Twice-weekly foliar applications of Ca (432 ppm) were begun at the stage of first bract coloration to attempt to prevent necrosis. In addition to bract necrosis, puckering of bracts occurred on controls but not in Ca-treated plants. In another experiment, induced Ca deficiency symptomology included bract necrosis. Calcium chloride spray essentially prevented the necrosis. Necrotic bract marginal tissue had 0.07% Ca, whereas sprayed tissue contained more than three times this Ca concentration.