Effect of photoperiod and daily light integral on flowering of five Hibiscus sp.

The effect of daily light integral (DLI) (400-700 nm) and photoperiod on Hibiscus sp. growth and flowering was studied. Hibiscus coccineus (Medic.) Walt., Hibiscus cisplatinus St-Hil., Hibiscus moscheutos L. 'Disco Belle Pink', Hibiscus radiatus Cav., and Hibiscus trionum L. plants were grown under a 9 h (0730-1630 h) or 16 h (0600-2200 h) photoperiod in a greenhouse under ambient daylight plus supplemental high-pressure sodium lighting at 20 ± 1°C. Within each photoperiod plants were grown under four levels of supplemental irradiance to achieve four DLIs. Under the 9 h photoperiod, plants received an additional 0, 2, 4, or 8 mol m^-2 per day. Under the 16 h photoperiod, plants received an additional 2, 4, 8, or 16 mol m^-2 per day. Increasing DLI from 8.3 to 25.5 mol m^-2 per day (ambient plus supplemental) decreased H. cisplatinus leaf number below the first flower from 26 to 18 leaves, regardless of photoperiod. DLI interacted with photoperiod to affect flowering of H. moscheutos and H. trionum. H. moscheutos leaf number below the first flower was 15 ± 2 leaves under a 16 h photoperiod, regardless of DLI. Increasing DLI from 12.2 to 20.2 mol m^-2 per day reduced H. moscheutos 'Disco Belle Pink' leaf number below the first flower from 24 to 18 leaves, under a 9 h photoperiod only. Increasing DLI did not affect H. trionum leaf number below the first flower bud initiated, but reduced leaf number below the first flower to open on plants grown under a 9 h photoperiod. H. radiatus flowered only under a 9 h photoperiod and leaf number below the first flower was not affected by DLI. Increasing DLI from 6.7 to 8.9 mol m^-2 per day increased H. radiatus total flower bud number at first flower opening from 7 ± 1 to 10 ± 1 buds, but did not affect flower bud number of the other species. H. coccineus did not flower during the experiment.