Greenhouse Propagation of Ornamental Ipomoea batatas Cultivars Under Light-emitting Diodes (LEDs) and Natural Light

Bedding plant growers are adopting new lighting technologies for faster and more vigorous establishment of unrooted bedding plant cuttings. Light emitting diode (LED) technology is quickly becoming less expensive for greenhouse installations with significantly reduced power consumption compared to high intensity discharge (HID) sodium lamps. Faster root formation with greater root mass decreases propagation time ultimately reducing crop time allowing for more turns per unit area in the greenhouse. The objective of this study was to compare the adventitious rooting of four popular Ipomoea batatas cultivars under LED light compared to natural light. The cultivars were ‘Black Heart’ (garnet-purple foliage), ‘Blackie’ (deep red/black foliage), ‘Margie Compact’ (lime green foliage), and ‘Tri-Color’ (white/pink/red foliage). Unrooted cuttings procured from a commercial propagator were stuck into perlite and placed under mist for 15 seconds at 10 minute intervals on 2 February 2016. Half of the study was under LED supplemental light and half under natural light. The double-wall polycarbonate greenhouse included 60% shade, which was pulled for the duration of the study. The study was conducted in Fort Collins, CO (40.5853° N, 105.0844° W). The LED treatment received 16 h supplemental light (Philips GreenPower LED toplighting) and the natural day length ranged from 10 h 8 m to 11 h 36 minutes, start to finish. Blocks of cuttings were harvested at 2, 3, 4, and 5 weeks after stick and the fresh weight of the roots was recorded. Ipomoea ‘Margie Compact’ and ‘Tri-Color’ under LED light had greater root fresh weight four weeks after sticking compared to those under natural light. Ipomoea ‘Black Heart’ and ‘Blackie’ under LED light had greater root fresh weight five weeks after sticking compared to those under natural light.