Photosynthetic Daily Light Integral Influences Growth, Morphology, Physiology, and Quality of Swordfern Cultivars

Boston and Australian swordferns (Nephrolepis sp.) are popular tropical ferns for hanging baskets and containers; however, greenhouse production occurs during times of the year when growers may need to deploy shade or supplemental lighting to manage the growing environment. Our objectives were to quantify the impact of the daily light integral (DLI) on growth, morphology, physiology, and ornamental quality of containerized Nephrolepis species and cultivars, and to establish optimal DLIs for containerized swordferns to assist commercial greenhouse growers with light management strategies during production. Eleven cultivars of Boston swordfern [N. exaltata (L.) Schott Blue Bells, Compacta, Fluffy Ruffles, Gold, Montana, Nevada, Petticoat, Pom Pom, Super, Tiger, and True] and one cultivar of Australian swordfern [N. obliterata (R. Br.) J. Sm. Western Queen] were investigated. Plants were grown for 58 days at 20 °C and placed under one of four different fixed-woven shadecloths providing ≈86%, 62%, 42%, or 26% shade or no shade, thereby establishing mean DLIs of 3.2, 6.4, 10.7, 12.4, and 17.1 mol⋅m−2⋅d−1, respectively. For most cultivars, the growth index, which is an integrated measurement of height and diameter, decreased linearly as the DLI increased from 3.2 to 17.2 mol⋅m−2⋅d−1, resulting in smaller compact plants. Increasing the DLI significantly affected the frond number of each cultivar differently, whereas dry mass generally increased as the DLI increased from 3.2 to 10.7 to 12.4 mol⋅m−2⋅d−1 for most cultivars. For each cultivar, as the DLI increased from 3.2 to 17.1 mol⋅m−2⋅d−1, the chlorophyll concentration index decreased, whereas the hue angle increased and chroma was unaffected. Our results indicate that growers should maintain ≈10 to 12 mol⋅m−2⋅d−1 during greenhouse Nephrolepis production; however, DLIs ≥5.5 mol⋅m−2⋅d−1 and ≤16.5 mol⋅m−2⋅d−1 also improved the quality of some Nephrolepis cultivars.