High-pressure Sodium Radiation during Off-peak Nighttimes Increases Cut Rose Production and Quality

Abstract

One-year-old plants of four cut rose (Rosa hybrida L.) cultivars were grown under either natural or supplemental irradiance for 4 months during the winter in Colorado. Supplemental irradiance with high-pressure sodium (HPS) lamps was supplied at 100 μmol·m–2·s–1 for 10 h each night during off-peak electrical use periods. Total cut flower yield, stem length, and fresh weight of individual flowers were recorded. The number of flowers produced and fresh weight increased for all cultivars under the supplemental irradiance treatment. Flower count, stem length, and fresh weight showed significant differences among the four 4-week production periods; production differences were promoted through pinches of two stems per plant to time for holiday peaks. When production was highest, stem length and fresh weight were lower, most likely due to redistribution of the limited carbohydrate pool during the winter.