Prolific production of offspring is generally characteristic of invasive plant species. However, Allee effects and other population-level processes may constrain reproductive success. This study identified variation in seed quality resulting from different genetic diversity levels in parental populations of an invasive grass. Using the outcrossing and wind-pollinated annual grass Lolium multiflorum, experimental populations were created with independently varying size and genetic diversity. Seeds from parental populations with lower diversity germinated and emerged from the soil at significantly lower rates than seeds from populations with the highest diversity. This effect was not detected in later-occurring fitness components such as flower production per planted seed. Reductions in seed germination and seedling numbers can affect future generations by reducing the size and/or genetic diversity of the resulting populations. The reduced offspring quality seen here suggests that fecundity and invasiveness vary not only among invasive species or potential invasive species, but also among populations of the same invasive species and highlights an advantage of genetic diversity within invasions.