Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


The performance of seventeen cultivars of poinsettias grown under three temperature regimes in four crops was studied to determine the effects of temperature on plant quality and to determine a base temperature for each cultivar. Growth factors such as shoot height, node number, bract spread and flower size increased with increases in temperature. Bract number increased with cooler temperatures. Less time was needed for coloration and anthesis at the warm regime. Varietal responses varied with temperature with the cultivars 'Annette Hegg Diva', 'Gutbier V-10', 'Annette Hegg Dark Red' and 'Annette Hegg Supreme' achieving best quality in the cool regime. Lower base temperatures were derived by regression equation method when more replications were utilized in each crop. In testing these base temperature values, better agreement between treatments in total degree-day summation values were also obtained when more replications were utilized. Since perfect agreement was not reached, this would indicate that lower base temperature values could be used. It was concluded that more replications and weekly measurements of average temperature and growth could be taken to utilize the stage of development of that cultivar for a correct base temperature. It was further concluded that if total crop time at 18.3(DEGREES)C were used as a base, a 16.6% net savings in energy would occur.