Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


The effects of natural day photoperiod, 18 or 20 days of initial, artificially long photoperiod, and 25 or 27 days of initial, artificially long photoperiods upon the variables of date of finish, percentages of plants finishing for selected sales periods, theoretical date of floral induction, final height, number of leaves, average internode length, number of bracts, bract spread and cyathial cluster diameter for a total of 18 commercially important cultivars of Euphorbia pulcherrima Willd. (poinsettia) were studied. In a related study, the effects of three different pinching dates on the above mentioned variables for the same cultivars were investigated. In general, the influence of lighting regimes was greater than that of pinching date. Plants grown on natural days and pinched early finished early when compared to other treatments. Of all the variables measured, date of finish, percentages of plants finishing for targeted sales periods, height, number of bracts, and bract spreads were most profoundly affected. The reported dates of floral induction and the reported response groupings for the particular cultivars were found to be, in most cases, not valid in Baton Rouge, Louisiana. Although all of the treatments affected all of the measured variables, almost all of the plants grown for this study were considered quite acceptable for peak sales periods. The relationships among cyathial cluster diameter, number of bracts and bract spreads were discussed.