LAMP TYPE AND IRRADIANCE LEVEL FOR DAYLENGTH EXTENSIONS INFLUENCE FLOWERING OF CAMPANULA-CARPATICA BLUE CLIPS, COREOPSIS-GRANDIFLORA EARLY SUNRISE, AND COREOPSIS-VERTICILLATA MOONBEAM

The effectiveness of cool-white fluorescent, high-pressure sodium, inc andescent, and metal halide lamps for inducing flowering through dayle ngth extensions in Campanula carpatica Jacq. 'Blue Clips', Coreopsis g randiflora Hogg ex Sweet 'Early Sunrise', and Coreopsis verticillata L . 'Moonbeam' was compared. Lighting was delivered as a 7-hour day exte nsion with photosynthetic photon flux (PPF) ranging from 0.05 to 2.0 m u mol.m(-2).s(-1) following a 9 hour natural daylength. Threshold irra diance values for flowering ranged from <0.05 to 0.4 mu mol.m(-2).s(-1 ), depending on species. Saturation irradiance values for Campanula ca rpatica 'Blue Clips' and C. grandiflora 'Early Sunrise' were between 0 .2 +/- 0.2 and 0.7 +/- 0.5 mu mol.m(-2).s(-1), and did not differ betw een lamps. An irradiance of 1.0 mu mol.m(-2).s(-1) from any lamp was a dequate for flowering in Coreopsis verticillata 'Moonbeam'. Time to fl ower at irradiances above the saturation points did not differ signifi cantly between lamp types for all species tested. Campanula carpatica 'Blue Clips' and Coreopsis grandiflora 'Early Sunrise' plants had sign ificantly longer stems under incandescent lamps than in any other trea tment. Coreopsis verticillata 'Moonbeam' plants grown under cool-white fluorescent lamps had stems approximate to 10% longer than those grow n under high-pressure sodium or incandescent lamps.