This is our first year in this house and discovered that there is a large grove of cottonwood trees in a greenbelt down the street. During spring our yard was covered with cotton -- we tried to clean it up but obviously didn't do a very good job because all of our planting beds, flagstone joints, and gravel paths have been full of cottonwood seedlings all sprint and summer. I pull out buckets of this stuff every week but a few days later it's as thick as ever. It seems endless! Any suggestions to get rid of all these seedlings growing in my mulch? I'm debating re-mulching but am worried that somehow the cottonwoods will find their way through and I'll be pulling them out again in a few weeks.

Thanks for your help!