Weed infestations are primarily driven by the weed seedbank, making it essential to reduce seedbank replenishment for effective control. Seed shattering or retention is a weed plant-specific characteristics and can vary for different weed species, their cohorts or biotypes/populations and weather conditions. Seed shattering phenology of Phalaris minor and Avena ludoviciana and possible drivers (such as total number of seeds per panicle, plant height, number of tillers and plant biomass) for seed retention was studied at wheat harvest in a two-year study at Punjab Agricultural University, Ludhiana. The results suggested that 74% and 9% seed retention of P. minor and A. ludoviciana, respectively at wheat harvest. The plant biomass played a critical role in seed retention for P. minor, while none of the tested predictors significantly influenced retention in A. ludoviciana. This highlighted the weed species-specific differences in seed retention mechanisms, which could be essential for understanding their ecological and management implications. It is concluded that P. minor may be a suitable candidate (with 74% seed retention) for harvest weed seed control (HWSC) approaches while A. ludoviciana (with 9% seed retention) cannot be targeted with this approach.