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

Abstract

Hibiscus rosa-sinensis, Rosa sp. (miniature roses), Sinningia speciosa, Gerbera hybrida, Kalanchoe blossfeldiana, Hydrangea, Begonia x hiemalis, Calceolaria, Cyclamen persicum and Pelargonium domesticum were grown at six photon flu x densities (85, 130, 170, 215, 255 and 300 μmol·m -2 ·s -1 , PFD) during lighting periods of 20 h·day -1 at three air temperatures (18 ° C, 21 ° C and 24 ° C) in midwinter 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 increase 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 recommended for Calceolaria and Cyclamen, of 8 to 10 mol·m -2 ·day -1 for Sinningia, Gerbera, Kalanchoe, Hydrangea and Begonia, of 10 to 12 mol·m -2 ·day -1 for Pelargonium and of 12 to 15 mol·m -2 day -1 for Hibiscus and miniature roses.