By Carol Stocker, Boston Globe garden writer...Weeds with deep tap roots such as dock make very beneficial compost. There are some invasive weeds you wouldn't want to compost. These include most vines and other plants that can sprout from a small piece of root such as poison ivy, bindweed, bittersweet, English ivy, goutweed, or witch grass. Most weeds are not a problem however, if they are added to the compost pile before they've gone to seed. Never add the cut stalks of Japanese knotweed or bamboo, however, which can produce new plants.