ASHS 2025 Conference

Small-scale growers face challenges in optimizing the quantity and quality of new broccoli cultivars due to shifting weather patterns and the prevalence of heat-sensitive cultivars. This study aims to identify high-performing cultivars and optimal planting dates for late spring to enhance the competitiveness of cool-season specialty crop growers in North Dakota. The research took place at the NDSU Horticulture Research Farm, near Absaraka, ND, to examine how planting time impacts cultivar performance through field experiments on four planting dates: May 1st, May 15th, June 1st, and June 15th. Early planting of broccoli, particularly in May, resulted in higher yields and better quality across all cultivars. Some cultivars outperformed others. 'Jacaranda' yielded significantly more than any other cultivar, which is a noteworthy. Conversely, 'Gypsy' and 'Monty' had yields similar to the standard cultivar 'Green Magic', while 'Purple Peacock' yielded less across all planting dates, indicating poor adaptation. Early planting benefited all broccoli cultivars, with later dates bringing higher temperatures that negatively impacted head formation and curd size across all cultivars. These elevated temperatures alter key physiological parameters, such as increased transpiration and vapor pressure deficit, while potentially reducing photosynthetic efficiency and stomatal conductance. The physiological changes induced by higher temperatures ultimately lead to accelerated maturation, smaller heads, and reduced overall yields. Notably, early planted broccoli potentially achieved up to 35% higher yields than late-planted crops. The findings provide valuable insights into the relationships between planting dates, temperature effects, and cultivar-specific responses, emphasizing the importance of these factors in maximizing yield and quality for cool-season specialty crop growers in the region.