ASHS 2025 Conference

The propagation of ornamental woody nursery liners (young plants) is primarily through stem cuttings to maintain genotypic and phenotypic uniformity. The application of rooting hormones is common practice in stem cutting propagation to hasten, promote uniformity, and enhance the quality of adventitious rooting. Rooting hormones are traditionally applied by dipping cuttings into solutions or powders. However, these methods increase labor costs, cutting stress, and opportunities for contamination. Foliar applications of rooting hormones would improve production efficiency, reduce cutting contamination and stress, and allow for multiple hormone applications after sticking. Thus, there is a critical need to identify the optimal rates of foliar rooting hormones to improve and maximize adventitious rooting in woody nursery taxa. Therefore, this study aimed to quantify the impact of foliar rooting hormones 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 of fixed 4-mil clear construction film. The greenhouse was set at 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. At 1 d after sticking, cuttings were sprayed with a solution containing clear tap water and 0, 500, 1,000, 1,500, 3,000, or 6,000 mg·L–1 20% indole-3-butyric acid (IBA) at a volume of 1.89 L·m–2. After 42 d, data was collected including callusing and rooting percentage, stem length and caliper, leaf area, and shoot and root dry mass. In general, increasing IBA foliar application concentration improved rooting success and uniformity to different magnitudes among species. For example, rooting percentage of Chamaecyparis increased by 67% as foliar IBA concentrations increased from 0 to 6,000 mg·L–1 IBA. The results of this study determined the optimal rates of foliar IBA application across an array of woody taxa to hasten adventitious rooting and improve quality for ornamental woody nursery liner production.