Influence of Reduced Night Temperatures on Growth and Flowering of ‘May Shoesmith’ Chrysanthemums1

Abstract Plants of ‘May Shoesmith’ chrysanthemum ( Chrysanthemum morifolium Ramat.) were grown in controlled environment chambers at optimal (16°C) and sup-optimal night temperatures. Reduced night temperatures were imposed for all or part of the night cycle. Number of days to flowering was delayed as night temperature decreased from 16° or as duration of reduced temperature during each diurnal cycle was increased. Compared to plants grown at a continuous 16° night temperature, plants grown at 10° for 9 or 10½ hours each night (with the remaining hours at 16°) had greater stem diameter, were taller and had flowers with greater diameter and fresh weight. Number of nodes was not affected.