All plants need sunlight to survive so if you don't want to uproot the onions (dig down and get the whole root) you can try smothering them with a layer of newspaper several pages thick topped with 2 to 5 inches of mulch. One more method is to cut the tops off, it will grow back, then cut them back to ground level again and repeat. Keep cutting off the tops and without any foliage the bulbs should eventually die out. Good luck, Keep growing, Marianne Binetti