This study investigates the effects of maize straw biochar application on the early growth of broccoli and cauliflower under coastal conditions in Southern Bangladesh. The experiment was conducted at Noakhali Science and Technology University over the winter cropping season (December–March), using a randomized complete block design with five biochar treatments (0, 2, 4, 6, and 8 tons/ha) applied before transplanting. Growth parameters, such as plant height, leaf number, and leaf breadth, were measured at 15 and 35 days after transplanting (DAT). Statistical analysis using R programming and two-way ANOVA revealed significant effects of crop type and biochar application. At 15 DAT, crop type influenced plant height, while biochar significantly enhanced plant height and leaf breadth by 35 DAT, though its effect on leaf number was transient. The transient nature of biochar's effects on leaf number and plant height emphasizes the importance of crop type and timing of the application. Final biomass and yield assessments are part of the full-season study and will be presented in subsequent publications, complementing these early growth findings. These findings provide insights for optimizing biochar use in sustainable agriculture in salinity-prone coastal regions.