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.

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.

Tea (Camellia sinensis) was first grown commercially in the Pacific Northwest in Salem, OR in 1988 (Minto Island Growers), and cv. Minto Pacific, selected at that site, was established in a small-scale planting in Burlington, WA in 1997. To test other cultivars for production in the Pacific Northwest region, the successful Washington State University (WSU) vegetative propagation method for ‘Minto Pacific’ was carried out with 14 tea cultivars at WSU Northwestern Washington Research and Extension Center (NWREC): BL1, BL2, Large Leaf, Small Leaf, Christine’s Choice, Dave’s Fav, Sochi, Black Sea, var. Assamica from Mississippi State University; Yukata Midori, Benikaori, Yabukita, Bohea from the USDA National Plant Germplasm System (NPGS) in Hilo, Hawaii; and Minto Pacific from Burlington (year 2 only). For this 2-year greenhouse propagation trial, tea shoots arrived at WSU NWREC on 16 Aug (Mississippi) and 14 Sept 2023 (Hawaii) for year 1, and 16 Sept (Mississippi), 23 Sept (Hawaii) and 25 Sept 2024 (Burlington) for year 2. Both years, shoots were processed into one-node cuttings within 1 day of arrival, the bottom stem of each cutting was scored with a knife, dipped into a rooting hormone for 5-10 seconds, then placed into a treepot filled with a propagation medium (peatmoss, vermiculite, perlite, 5:3:2 ratio). Cuttings were placed in a misting chamber in the greenhouse for 1 year, then moved to a greenhouse bench for 7 months. In February 2024 (Year 1), overall plant survival was 83%, average plant height was 1 cm, plants had 2.5 leaves on average, and the average plant health rating was 4.9/5. Cv. Large Leaf (100%) had the highest survival followed by Dave’s Fave (98%) and Black Sea (98%), while Benikaori (60%) and BL1 (62%) had the lowest survival. In October 2024, the final overall plant survival was 31%, average plant height was 35 cm, plants had 19 leaves on average, and the average plant health rating was 3.6/5. Cv. Christine’s Choice (46%) had the highest survival followed by Large Leaf (43%) and BL2 (42%), while Benikaori (13%) and BL1 (15%) still had the lowest survival. In January 2025 (Year 2), overall plant survival was 73%, average plant height was 2 cm, plants had an average of 1.2 leaves, and average plant health rating was 4.2/5. Cv. Minto Pacific had 100% survival followed by Large Leaf, Christine’s Choice, and Assamica (all 95% survival), while Benikaori (40%) and Sochi (51%) had the lowest survival.

Plants evolved with roots in the soil, providing a temperature buffer to the root zone most of the year. However, as the nursery industry has primarily moved plants out of the ground and into thin plastic containers with very coarse organic substrates, we are faced with added challenges of managing substrate temperature to ensure healthy plant production. Moreover, resource efficiency, particularly regarding mineral nutrients, is a critical factor in the long-term success of the nursery industry. Fertilizer release is controlled by water and temperature in container-grown ornamental nursery production systems. Thus, it was hypothesized that pragmatic management of substrate temperature and moisture could extend the longevity of controlled-release fertilizer in a container system. This study was conducted to determine the effect of irrigation scheduling, container color, and stratified substrates on substrate temperature management, crop health and development, and fertilizer longevity. ‘Limelight’ Hydrangea (Hydrangea paniculata) were grown in either black or white containers and subjected to a single daily irrigation or the same volume applied in three increments throughout the day (cyclic). Hydrangeas grown in white containers with cyclic irrigation increased plant growth by up to 50% compared to those grown in black containers with single-application irrigation, and stratified substrates reduced phosphorus leaching by 30%. Across all treatments, plant health, root development and fertilizer efficiency were improved with substrate temperature management strategies. The results indicate growers should pursue root zone temperature mitigation strategies to enhance crop growth and salability, increase fertilizer use and efficiency, and decrease phosphorus leaching from nursery containers.

Efficient and accurate counting of plants is critical for nursery inventory management to support yield prediction, sales forecasting, and monitoring. Current practices in nurseries depend heavily on manual methods, which are labor-intensive and prone to errors. Researchers have made efforts in utilizing computer vision and deep learning to address these issues, yet a seamless solution for plant counting and inventory management remains unavailable. Image-based counting systems often struggle with classification accuracy in diverse, real-world scenarios, while tracking plants in videos faces challenges such as identity switches, misclassifications, and varying field conditions, limiting the reliability of existing methods. To overcome these challenges, we developed a cloud-based complete solution specifically for ornamental plant nursery inventory management. Our system introduces a novel tracking algorithm KBTrack, optimized for precision and scalability. At its core is an ensemble deep learning model that combines a transfer learning-based YOLOv11 and a CutMix-enhanced YOLOv11 model for plant detection. The KBTrack was developed on top of ByteTrack multi object tracking framework by adding a layer that compares segmentation masks across multiple frames for long term matching of the objects. This addition addressed identity switches and misclassifications, ensuring accurate plant counting even in complex field conditions. The segmentation capabilities of YOLOv11 are also utilized to generate masks for individual plants, enabling customizable plant-specific quality assessments through an interactive dashboard. The system utilizes GPS to allow users to monitor nursery plant beds on a map making it easier to monitor and track changes and updates across the plant beds. The platform is deployed in cloud with a microservice architecture where users can upload field videos and access results through an intuitive interface designed to ensure scalability. To evaluate the capabilities of the proposed framework, data was collected using an autonomous ground vehicle equipped with an OAK-D Pro camera, capturing 4K resolution videos. Experiments conducted on Azalea and Sunshine plants demonstrated the system's effectiveness, achieving a high mAP@50 of 0.982 for detection and 0.981 for instance segmentation on the ensemble model, MOTP 0.916 in the KBTrack multi object tracking algorithm and counting accuracy of 0.988 with an RMSE of 0.669. This confirms its ability to accurately detect and track plants. This solution provides a robust framework for addressing the limitations of current methods, offering an effective and scalable approach to modernize ornamental plant inventory systems.

Hydrangea (Hydrangea macrophylla) is a widely cultivated ornamental nursery crop, but its vigorous shoot growth often necessitates labor-intensive pruning or repeated applications of plant growth regulators (PGRs) to achieve saleable quality. As a result, methods to reduce reliance on pruning or PGRs are highly desirable to growers. One potential alternative is the use of shade netting, which is commonly used in nursery production to protect sensitive plants from excessive solar radiation. This includes hydrangeas which are frequently grown under 30–50% black shade netting. Beyond reducing light intensity, shade nets can also alter the light spectrum, adjusting the relative quantities of blue (400–499 nm), green (500–599 nm), and red (600–699 nm) light, which may affect plant morphology. Blue shade nets, which primarily absorb green and red light, are often marketed as tools to produce more compact shoot growth and thus could serve as an alternative to pruning or PGRs. However, little information exists on the use of blue shade netting to control hydrangea shoot growth. This study evaluated the effects of shade color (black, blue, red, and grey) and blue shade percentage (40–75%) on the growth of hydrangea ‘Twist and Shout’ in a nursery and a greenhouse trial. In the nursery trial, hoop houses were covered with either 30% black, 30% blue, 30% red, or 45% grey shade netting. In the greenhouse trial, chambers were covered with either 40% blue, 50% blue, 75% blue, or 50% black shade netting. Growth parameters including canopy height, width, volume, projected canopy area, leaf length, and chlorophyll concentration were measured repeatedly over a 49-day growth period. Results from the nursery and greenhouse trial showed that shade percentage, not shade color, was the dominant factor influencing shoot growth. Thus, colored shade netting did not suppress plant vigor or reduce the need for pruning or PGRs. These findings suggest that 30% black shade was ideal for hydrangea production, and altering the color of shade netting provided no additive benefits. While ineffective for hydrangea production, nursery crops that benefit from higher percentages of shade such as Hosta plantaginea, may benefit more from colored shade netting.

Nursery and greenhouse growers and dealers in the United States contribute significantly to the economy, environment, and food systems. Nursery and greenhouse operations provide a wide range of plants critical to residential and commercial landscaping, habitat creation for pollinators, and essential planting materials for fruit, vegetable, and ornamental crop production. The sustainability of these operations, as with other agricultural productions, highly relies on water availability, making it significant to evaluate the future of water and climatic risks throughout the United States. This study focuses on the critical part of this evaluation, developing a map of licensed greenhouse and nursery growers and dealers throughout the United States, using information received directly from state officials and agency websites. Texas, Florida and California were revealed to have the most HRI operations (growers and dealers), but the latter two states have the most growers. Region-wise, the Southeast and Northeast regions have the most nursery growers, with the Northern Rockies and Plains and the Southwest regions having the lowest numbers, although states like Utah, Arizona, and Idaho are currently missing in our analysis due to data unavailability and complexity. This mapping exercise will be followed by overlaying climatic indices such as precipitation, temperature and drought forecasts, to evaluate growers' state and regional vulnerability to water and climatic risks. This will aid in assessing climate-related risks, guide adaptive strategies, and support sustainable nursery management across diverse environmental zones.