2019 ASHS Annual Conference

Successful rooting and establishment of herbaceous bedding plants during mid-winter in the greenhouse can be a challenge due to photoperiod, nutrition, and other environmental variables. This trial focused on supplemental LED light spectrum and its effects on adventitious rooting of five cultivars of annuals, and five cultivars of perennials. Unrooted cuttings acquired through a commercial broker were stuck into rooting cubes and placed under intermittent mist in a polycarbonate greenhouse in late January 2018. Two supplemental light treatments and one treatment with no supplemental light were used. The first supplemental light treatment used Philips DR/W/FR (deep red/white/far red) GreenPower LED toplight modules and with the second Philips DR/W/MB (deep red/white/medium blue) GreenPower LED toplight modules. Each supplemental light treatment provided 90 µmols·m²·sec² photosynthetic active radiation (PAR) as daylight extension for 8.5 hours each day. After two weeks each plug was examined, and the number of visible roots were counted and once again one week later. All species had greater number of roots under supplemental light. Geranium and rosemary cuttings generated more roots under DR/W/MB compared to DR/W/FR and no supplemental light, respectively. Osteospermum, phlox, salvia, and scaevola cuttings generated more roots under DR/W/FR. Leucanthemum rooted more quickly under DR/W/MB, but one week later, rooting under both supplemental light treatments were similar. Calibrochoa, iberis, and sage rooted similarly under both light treatments, but rooting was greater compared to supplemental light. Our results indicate that supplemental light improves the initial rooting under mid-winter greenhouse conditions. The spectra for best rooting is dependent on cultivar.