Experts and BHG readers answer.
Wild onions (Allium stellatum) are stubborn plants that seem to have no easy way to get rid of them. Onions develop clusters of small bulblets around the main one, and it is easy to leave the smaller ones in the ground. The most reliable method is to dig them with a sharp knife, hand weeder, or small digger, making sure that the whole clump comes up. It is not enough to just pull them by the leaves as usually there are lots of bulblets left behind and these will multiply. If you are conscientious about removing them, in a couple of years they will be gone.