For many invasive plants, seed dormancy and persistence facilitate population expansion. These traits also complicate control efforts, as new seedlings may continue to emerge for years after the removal of existing plants. The maximum longevity of invasive plant seeds may range from years to decades. However, few seeds emerge after such a long time under field conditions. We conducted a field experiment testing the impact of seed burial depth on emergence of meadow knapweed (Centaurea × moncktonii C.E. Britton) and spotted knapweed [Centaurea stoebe L. subsp. micranthos (Gugler) Hayek] over 3 years. For C. × moncktonii, emergence (raw data corrected for seed viability) was 57% at 0 cm, 28% at 2 cm, 3% at 4 cm, and 0% at 8 cm. For C. stoebe, emergence was 84% at 0 cm, 11% at 2 cm, 4% at 4 cm, and 0% at 8 cm. The primary flush of seedlings, averaged over Centaurea species and burial depths, occurred during the first few months of the study in fall 2018. Little emergence occurred after spring/summer 2019, although the study continued through spring/summer 2021. Our findings clarify the maximum burial depth from which these Centaurea species can emerge and demonstrate that emergence is concentrated in the first year after seed production.