Optimum sowing date and cultivar duration of dry-seeded boro on the High Ganges River Floodplain of Bangladesh

•Dry seeding of boro crops in the High Ganges River Floodplain is risky.•Cold damage in January will kill crops sown in November in at least 2% of years.•Early November sowings emerged faster than late November sowings.•Yield of BRRI dhan28 and 29 was maximum for 8–15 November sowings.•Cultivars with greater vegetative cold tolerance are needed to enable dry seeding.