The Effect of Photosynthetic Active Radiation and Temperature on Growth and Flowering of Ten Flowering Pot

PFD) during lighting periods of 20 h∙day−1 at three air temperatures (18˚C, 21˚C and 24˚C) in mid-winter at latitude 59 ˚ north. This corresponded to photosynthetic active radiations (PAR) ranging from 6.1 to 21.6 mol∙m−2∙day−1. Time until flowering decreased in all species except Cyclamen when the temperature increased from 18˚C to 21˚C, particularly at lower PFD levels. A further in-crease in temperature, from 21˚C to 24˚C, clearly decreased time until flowering in six of the ten tested species. Generally, this represented a reduction in the time until flowering between 20% and 40%. The dry weight of the plants at time of flowering increased up to 170 µmol∙m−2∙s−1 PFD (12.2 mol∙m−2∙day−1 PAR) in Hibiscus, miniature rose, Kalanchoe and Pelargonium, while the dry weight reached a maximum at 85 to 130 µmol∙m−2∙s−1 PFD mol∙m−2∙day−1 (6.1 to 9.4 mol∙m−2∙day−1) in the other species. Based on the present results a PAR level of 6 to 8 mol m−2∙day−1 is recom