Use of light emitting diode (LED) technology is beginning to replace traditional lighting in greenhouses. This research focused on the effects of LED lighting and gibberellic acid supplementation on growth and flowering of Dahlia
spp. ‘Karma Serena’, Liatris spicata
‘Kobold’, and Lilium asiatic
‘Yellow Cocotte’. Light treatments, used to extend photoperiod, included LED flowering lamps and halogen lamps that emitted a combination of red + far-red + white, red + white, and broad spectrum from late fall to early spring. Gibberellic acid treatments ranged from 40 to 340 mg L−1
for Asiatic lily ‘Yellow Cocotte’, 50 to 250 for gayfeather ‘Kobold’, and 50 to 150 for dahlia ‘Karma Serena’. Results varied within species in response to light and gibberellic acid. A significant interaction of light with gibberellic acid influenced mean flower number and flowering percentage for dahlia ‘Karma Serena’, while flowering percentage and flower diameter were influenced for Asiatic lily ‘Yellow Cocotte’. Effect of light was most significant on growth and flowering measurements, especially for gayfeather ‘Kobold’ and dahlia ‘Karma Serena’. For gayfeather ‘Kobold’, flowering occurred two weeks earlier under sole LED lighting than under other light treatments and no supplemental light. Although flowering occurred the earliest for dahlia ‘Karma Serena’ under no supplemental light, plants under light treatments had greater height, width, and shoot weight. Significant effects of gibberellic acid on growth and flowering measurements for dahlia ‘Karma Serena’ and Asiatic lily ‘Yellow Cocotte’ were observed for height, width, and flower number.
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