<p>Timely planting of sugar beet is essential to ensure optimal growth and sugar yield; yet, spring rainfall and crop rotation often delay planting, leading to yield loss and lower sugar recovery. Understanding agronomic strategies to overcome these challenges is therefore crucial for maintaining productivity under variable field conditions. This study aimed to evaluate whether seed hydropriming and foliar application of humic acid could mitigate the adverse effects of delayed planting on photosynthetic efficiency, root yield, and sugar quality of sugar beet (<i>Beta vulgaris</i> L.) under field conditions in Asadabad, Iran, during 2021 and 2022. A split-plot factorial experiment was conducted with four planting dates (March 25, April 8, April 22, and May 6) as main plots, and seed hydropriming (primed vs. unprimed) and humic acid foliar application (0.6% vs. water) as subplots. Results showed that delayed planting (May 6) increased sugar content but decreased root yield and white sugar yield. Seed hydropriming and humic acid application enhanced root yield by 17.6% and 19.8% and white sugar yield by 24% and 19.8%, respectively. Both treatments improved leaf area index, stomatal conductance, and photosynthesis, while reducing sub-stomatal CO₂ concentration and harmful nitrogen accumulation, indicating enhanced photosynthetic efficiency and nitrogen metabolism. The interaction of planting date, hydropriming, and humic acid significantly affected sodium content and stomatal conductance. Overall, the results demonstrate that integrating seed hydropriming and foliar humic acid provides an efficient, low-cost approach to reduce the negative impacts of late planting, improving sugar beet yield and quality under suboptimal growing conditions.</p>