EFFECTS OF AIR HUMIDITY, LIGHTING PERIOD AND LAMP TYPE ON GROWTH AND VASE LIFE OF ROSES

The rose cv, Souvenir was grown at two air humidities (65% and 90% rel ative humidity, RH) combined with three lighting periods (16, 20 and 2 4 h day(-1) at a photosynthetic photon flux of 170 mu mol m(-2) s(-1)) using high-pressure sodium lamps (HPS). In addition, fluorescent tube s were included at the two air humidities at 20 h day(-1). It was foun d that raising the humidity generally slightly increased the shoot len gth, while time until flowering was slightly reduced at the longest li ghting period and increased at the two shorter righting periods. Time until flowering and shoot length were slightly reduced but shoot fresh weight was unaffected by an increase in the lighting period. Fluoresc ent light gave shorter and lighter shoots as compared with HPS light. Increasing the air humidity reduced the vase life of the roses from 8- 13 to 2-5 days, while increasing the lighting period from 16 to 24 h d ay(-1) at 65% RH reduced the vase life from 13 to 8 days. Shortening o f vase life was caused by the early development of bent necks and leaf drying. Measurements of leaf diffusion resistance showed that the sto mata did not close during the dark period when the roses were grown at high air humidity, and this was particularly the case when grown unde r a lighting period of 20 h day(-1). The water-loss curves of detached leaves from shoots grown at 65% RH showed slight differences between the different lighting periods. The rate of weight loss of leaves from shoots grown at 90% RH was much greater than that at 65% RH, and incr eased with increasing lighting period. (C) 1998 Published by Elsevier Science B.V.