Gene-flow between intensively and extensively farmed grass populations is an ongoing feature of agroecological landscapes, especially in Atlantic northwestern. Europe. Adjoining population boundaries and in-field admixture of grass types via winter forage dispersal facilitates both in-field hybridisation and recruitment of immigrant seedlings. Here we examine the paternal hybridisation of one grass species (Lolium multiflorum, pollen donor) into the population of a second, fully inter-fertile, grass species (L. perenne, pollen receptor) via pollen-mediated gene-flow in an experimental field plot. Using weekly counts of successful pollination in 470 individual receptor plants based on paternity analysis in 4281 germinated F-1 seedlings, we determined the extent of evident hybridisation (hybrid progeny that show some paternal morphology) and silent hybridisation (hybrid progeny that show no paternal morphology) over the course of floral anthesis. Co-dominant morphological traits in F-1 progeny underestimated microsatellite-validated genetic hybridisation by approximately 30%, while background pollen competition dampened the overall rate of successful pollen donor pollination. Overall pollination from the donor plot followed a composite decline model. However over the course of floral anthesis the successful pollination pattern was changeable, and showed varying levels of affinity to three tested decline distribution models.