Enhancing quality in Bidens ferulifolia: interplay of light extension and growth retardants in greenhouse cultivation

This study examined the effects of photoperiod extension (16-hour day) and growth retardant application during the liner stage (weeks 5–11) on nutrient uptake and plant quality in two Bidens ferulifolia cultivars (Fire&Spicy and Hot&Spicy). Treatments included supplemental lighting (L), growth retardant (R), both (L-R), and a control (NL-NR). Mature plants were assessed for plant architecture, flowering, nutrient status, photosynthetic pigments, and soluble sugars. All plants branched vigorously, but L-R produced the most commercially favourable structure, with fewer long shoots and more short ones. L-R also yielded the shortest shoots and highest dry mass, especially in Hot&Spicy alongside increased P and Zn. Retardants reduced fresh mass but increased levels of N, P, K, S, and Cu, while decreasing Fe and Mn. Light-treated plants have more fully open flowers but had similar bud numbers. Supplemental light improved nutrient accumulation, chlorophyll a, carotenoids, and sugar content, indicating better physiological efficiency. Cultivars responded differently to R, with Fire&Spicy showing greater micronutrient uptake. Combining light and retardant during the liner stage enhances visual quality and nutrient efficiency in B. ferulifolia, offering growers a strategy to improve crop performance while potentially reducing reliance on chemical growth regulation.