ASHS 2025 Conference

Ornamental woody nursery plants are primarily propagated from 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 technologies to precisely control the environment. Thus, there is a critical need to identify cost-effective strategies, such as providing root-zone heating, to improve and maximize adventitious rooting. Root-zone heating has been used extensively to hasten adventitious rooting and increase root density in various plant species. However, optimal root-zone temperatures are largely unknown for many woody nursery crops. Therefore, this study aimed to quantify the impact of root-zone temperature on root growth and development of ornamental nursery cuttings. Unrooted stem cuttings of four ornamental nursery taxa were obtained from commercial nurseries. Cuttings of each taxon were individually inserted into 6.4-cm diameter containers filled with a propagation substrate. Cuttings were placed in a 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. A closed-loop root-zone heating system circulated hot water (49 °C) across greenhouse bench-tops. Forty-eight cuttings of each taxon were placed in root-zone heating environments with set points of 21, 24, 27, 30, and 33°C. 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 extent root-zone temperature can be leveraged to hasten adventitious rooting and improve liner quality.