Reblooming in pots is even more impressive as the soil temperature is lower and freeze and thaw more prominent. This 'twas the winter of little snow and mininal arctic blasts. When this happens, plants that are marginally hardy, those which might survive as perennials a few hundred miles south, come back with a vengeance--at least until chilly winter returns.
Weed killers cause toxic phosphate runoff into lakes and streams. Much of our area is watershed, thus the individual homeowner's impact on the enviroment is exponentially higher than communities on drier flatter ground.
Michigan is never the same place twice, so enjoy the minor aberations of nature, and start pullin' those weeds!