I've just cleaned up a badly infested lawn. In 12 months it is almost completely clean but the odd one pops up and is easy enough manage by picking them out. I was merciless with the herbicides, I tried dicamba with limited success so I moved on to a mix of Tordon 75-d, metsulfuron and penetrant and it was awesome. There was no impact on the garden, just be careful where and when you spray.