Here’s a rough graph of germination rate from field collected seed of the invasive weed I work on, Centaurea diffusa (seen here). Each point represents a different maternal plant from 57 different populations, with native individuals in red and invasive individuals in black. I have collections that were up to 8 years old when I ran this trial, and no decrease in germination rate! That’s just silly! I’m sure it doesn’t hurt with the being invasive and all.