Industrial Hemp Response to Waterlogging Stress: Influence of Duration and Growth Stage on Physiological Performance and Yield

Industrial hemp is often considered sensitive to waterlogging; however, empirical evidence remains scarce. This study evaluated the effects of waterlogging duration and timing on the physiology, growth, and development of hemp under controlled conditions. Two glasshouse experiments were conducted using industrial hemp (Cannabis sativa L.) cv. Ferimon 12. The first examined five waterlogging durations: 0 (control), 3, 6, 12, and 24 days, imposed at the eight true leaf pair stage. The second examined 3- and 6-day waterlogging events imposed at the six true leaf pair and flower initiation stages. In Experiment 1, waterlogging beyond 6 days caused severe damage, and plants died after 12 days of continuous waterlogging. Plants subjected to 3–6 days of waterlogging survived, but photosynthetic activity declined by 40–80%, biomass by 18–55%, and seed yield by 16–48% relative to the control, with the greatest reductions occurring after 6 days of waterlogging. Experiment 2 showed that plant sensitivity varied with developmental stage, with plants exhibiting greater susceptibility at the six true leaf pair stage compared to the flower initiation stage. The dual-purpose hemp cultivar Ferimon 12 was highly sensitive to waterlogging, particularly during early vegetative growth, with even short-term saturation impairing photosynthesis, stomatal conductance, growth and yield. These findings characterise the physiological limits of this cultivar under controlled conditions and demonstrate that developmental stage influences the severity of waterlogging impacts.