ASHS 2025 Conference

Eastern black walnut (Juglans nigra L.) is a long-lived perennial tree with significant potential for expanded cultivation and utilization. Renowned for its high-quality wood and nutritious nuts, it also presents opportunities for expanded horticultural application, including syrup production. Black walnut syrup has been suggested as a viable alternative or complement to maple syrup, offering a promising new species for syrup producers to explore. However, little is known about black walnut sap flow dynamics, sugar concentration, and how these traits respond to environmental conditions. This study evaluated sap flow patterns and sap quality during the 2024 and 2025 seasons using 25 mature trees from a research plot at the University of Minnesota Horticultural Research Center. Trees were tapped at the beginning of the sap season and monitored daily for sap volume and sugar concentration until the sap became cloudy, indicating bud break and the end of the collection period. Weather data were obtained from the Chaska, MN station via the Network for Environment and Weather Applications maintained by Cornell University. A linear mixed-effects model was used to evaluate the effects of year and genotype on sap volume and °Brix. Statistical models incorporating daily and lagged weather variables were used to assess environmental influences. Sap flow and sugar concentration varied across seasons and were not fully explained by single-day weather, suggesting more complex environmental dynamics. Total sap production was higher in 2024, with 307.4 L collected over 41 flow days. In 2025, the total sap volume was 227.6 L, collected over 37 flow days. In 2024, sap flow peaked in early March and followed a bell-shaped curve, while in 2025 the season began later and exhibited lower, more erratic daily yields. Average °Brix remained relatively stable across years, with slightly higher and more variable values in 2024. A subset of trees consistently exhibited high sap yield and sugar content across both years. The mixed-effects model revealed a significant year effect on °Brix, but not on sap volume, while genotype contributed to variation in both traits. These findings demonstrate that both genotype and seasonal conditions influence black walnut sap characteristics, supporting the potential for selecting high-performing trees to advance syrup production with this underutilized species.