Weed seeds are among the most patient organisms in nature. Many weeds can produce thousands of seeds per plant per year, and those seeds might lie dormant for decades, just waiting for the right conditions to sprout.

If you want to control weeds, then find where these seeds accumulate — in "seed banks."

"Gardeners should care because that's where all their seeds are coming from," said Ed Peachey, a weed science specialist with Oregon State University Extension. "If you don't prevent weeds from producing seeds, then you'll wind up with large seed banks, and always fighting with the weeds that e...