Cumulative Photosynthetically Active Radiation Research Articles

SUPPLEMENTAL HIGH PRESSURE SODIUM LIGHTING AND NIGHT TEMPERATURE EFFECTS ON SEED GERANIUMS

F1 seed-propagated geraniums (Pelargonium × hortorum Bailey) flowered earlier when plants received in excess of 400 E∙m−2 cumulative photosynthetically active radiation (PAR). Two out of three cultivars grown at 17 °C night temperature which received 443 E∙m−2 natural lighting or 341 E∙m−2 natural plus 102 E∙m−2 high pressure sodium lighting (HPS) over a 4-wk period following transplanting flowered earlier. Flowering was accelerated by 2 wks when a total of 920 E∙m−2 cumulative PAR (726 E∙m−2 natural plus 194 E∙m−2 HPS) was received by plants over an 8-wk period. Reducing night temperature from 17 to 13 °C delayed flowering by 2 wk. Supplementary HPS irradiation for 6–8 wk overcame the delay in flowering induced by low night temperature and produced compact plants with more shoots.

The Effect of Cumulative Photosynthetically Active Radiation on the Growth and Flowering of the Seedling Geranium, Pelargonium × hortorum Bailey1

Abstract Growth and flowering of Pelargonium × hortorum Bailey cvs. Sprinter Scarlet, Sprinter White, and Ringo were associated with cumulative photosynthetically active radiation (PAR); 41-65% of the variability in days to flower was attributed to cumulative PAR. Vegetative and total plant height decreased as cumulative PAR increased. The number of lateral breaks increased as irradiance increased while fresh weight showed no consistent pattern.