Abstract Blackgrass is a common winter annual grass weed in autumn-sown crop rotations in Atlantic European countries. Control with a minimum amount of herbicides in integrated cropping systems would be facilitated by modeling the effect of cropping systems on its demography. To develop the submodel relating weed seed bank to emerged seedlings, laboratory experiments were conducted to analyze and quantify seed germination and shoot elongation. These processes were studied as a function of environmental conditions during seed production (nitrogen availability, water deficit, plant density, and crop) and of seed characteristics (seed weight, harvest date, storage length, and dry-stored/soil-buried). Nonlinear equations relating germination and shoot elongation to time calculated as cumulated degree-days were fitted to the observed germination and shoot elongation data. These were used to estimate parameters for germination proportion and rate, as well as final shoot length and elongation rate. Recently harv...