The seeds take two years to sprout up through the ground.
VOA: special.2009.04.07
Having high expectations for even huge numbers of seeds to sprout when thrown on untilled land or clay, without any water, is probably going to lead to disappointment.
The droppings that cowbirds and other invaders leave behind can also contain seeds from invasive plants that will sprout, spread and ultimately change the soil so much that some forest salamanders and wildflowers can't survive, experts note.