Effects of photosynthetic daily light on swordfern cultivars

In the past decade, tropical ferns have increased in popularity for use in hanging baskets or as a potted indoor crop. To date, tropical ferns are the second largest (14%) category of the foliage plant sector in the commercial floriculture industry in the United States, with a reported volume of 12 million containers (hanging baskets and pots) representing a total sales value of $67.2 million US (US Department of Agriculture, 2020).

Although there are more than 120 tropical fern species available from commercial propagators, cultivars of Boston and Australian sword ferns (Nephrolepis sp.) are the most common taxa grown by greenhouse growers for hanging basket or container production. However, greenhouse production occurs during times of the year when growers may need to deploy shade or supplemental lighting to manage the growing environment.

The authors’ objectives in this study 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.

From liners (young plants), the production cycle for Boston sword fern cultivars requires 8 to 12 months. In general, production begins in June, when liners are transplanted to small containers for bulking. During this time, the ambient outdoor daily light integral (DLI) is 35 to 65 mol⋅m⁻²⋅d⁻¹); however, growers may need to deploy shade curtains to manage greenhouse temperatures, consequently reducing the DLI by 40% to 80%.

Furthermore, the DLI inside the greenhouse can be reduced by 50% or more from the greenhouse infrastructure, glazing material, and overhead hanging baskets. In fall, bulked plants are typically transplanted to larger containers or hanging baskets for subsequent growth and finishing during winter and early spring months. The DLIs during the growth and finishing stages of production can be as low as 5 to 10 mol⋅m⁻²⋅d⁻¹), especially across the northern United States.

Numerous studies have described the effect of the DLI on the growth, development, morphology, and physiology of annual bedding plants. However, there is a significant amount of variation among taxa regarding DLI requirements. This study examines the effects of DLI on growth, morphology, physiology, and, thus, overall quality and aesthetic value of 12 Nephrolepis cultivars.

The results show that, in general, growers should maintain ≈10 to 12 mol⋅m⁻²⋅d⁻¹ during greenhouse Boston and Australian sword fern production; In addition, greenhouse growers can deploy supplemental and/or day-extension lighting to increase the DLI during the months of late fall to early spring to improve the plant quality of Boston and Australian sword fern.

According to the authors, “This research was part of an undergraduate student senior capstone project establishing DLI recommendation for sword ferns under single or multi-layer hanging basket systems.”

The findings are published in the journal HortScience.