ASHS 2025 Conference

The primary form of propagation of ornamental woody nursery liners (young plants) is through stem cuttings to maintain genotypic and phenotypic uniformity. However, high rates of rooting failure in propagation remain a significant challenge, leading to economic loss. Greenhouses offer opportunities to leverage the environment for specific plant growth responses. Manipulation of the daily light integral (DLI) has been used extensively to hasten adventitious rooting and increase propagule quality in annual bedding plants, herbaceous perennials, and culinary herbs. Thus, there is a critical need to also identify the optimal DLI to improve and maximize adventitious rooting in woody taxa. Therefore, this study aimed to quantify the impact of DLI on root growth and development of ornamental woody nursery cuttings. Unrooted stem cuttings of four ornamental nursery taxa were obtained from commercial nurseries and individually inserted into 6.4-cm diameter containers filled with a propagation substrate. Cuttings were placed in a diffused glass-glazed greenhouse under a propagation environment with 20 °C air temperature, 80% relative humidity, and ambient daylight supplemented with ≈120 µmol·m–2·s–1 delivered from light-emitting diode arrays from 0600 to 2200 hr. Cuttings were rooted under fixed 4-mil clear construction film covered with one of four different fixed-woven shade cloths providing ≈72%, 52%, or 30% diffuse shading or no shade (0%). After 14, 28, and 42 d, data was collected including callusing and rooting percentage, root number, longest root length, stem length and caliper, leaf area, and shoot and root dry mass. The results of this study determined the optimal DLI, across an array of important woody taxa, to hasten adventitious rooting and improve liner quality.