Cultivar and Pinch Date Effect Poinsettia Leaf and Cyathium Retention in a Simulated Post Production Environment

Post production quality loss is a major issue for poinsettias (Euphorbia pulcherrima, Willd. ex Koltzsch) marketed through the modern market chain.  Growers face increasing pressure to produce quality plants with ever tightening profit margins, so reducing production costs without sacrificing product quality is vital. One potential cost saving strategy is producing poinsettias on a shortened production schedule which relies upon reduced vegetative growth time.  An experiment was designed to determine the effect of this reduced vegetative growth time on post production quality loss of pinched poinsettia plants quantified by loss of leaves and cyathia.  Rooted cuttings of poinsettia cultivars ‘Freedom Red’, ‘Prestige Early Red’, and ‘Advent Red’ were potted into 15-cm pots on 12 Aug. and pinched 4 Sept. or potted 19 Aug. and pinched 11 Sept.  ‘Freedom Red’ plants were grown with natural day length in Lexington, KY.  Night interruption lighting was used to delay ‘Prestige Early Red’ (lights out 25 Sept.) and ‘Advent Red’ (lights out 1 Oct.).  With this schedule all 3 cultivars were at a marketable stage of floral development on the pre-determined simulated shipping date of 21 Nov.  Plant growth regulators were used as needed.   All plants in the study were between 35 and 41 cm tall on 21 Nov.  Those plants that were pinched on 11 Sept. showed reduced leaf retention compared to those pinched on 4 Sept. following 18 days in a simulated post production environment (indoors under fluorescent lighting).  For example ‘Freedom Red’ plants pinched 4 Sept. and 11 Sept. retained 78% and 71% of leaves present on 21 Nov., respectively.  Plants with leaf retention below 75% were considered unmarketable.  There was also variability in leaf retention among the cultivars tested.  Plants of ‘Advent Red’, ‘Freedom Red’, and ‘Prestige Early Red’ pinched 4 Sept. retained 84%, 78%, and 67% of leaves present on 21 Nov., respectively.  There was no significant effect of potting and pinch date on cyathia retention so data were pooled for each cultivar.  After 18 days in the simulated post production environment ‘Advent Red’, ‘Freedom Red’, and ‘Prestige Early Red’  plants had dropped an average of 0.4, 0.9, and 4.5 cyathia per lateral branch.  The vegetative time allotted for poinsettia crops as well as the cultivar selected have a clear impact on the plants’ leaf and cyathia retention in post production.