The green parts of green onions regrow super fast when the onions are stored in a vase (or glass) of water like flowers. The only con of regrowing the greens this way is the whites quickly become unusable. The pro is the greens keep regrowing so that I now only buy green onions, which I use almost daily since my daughter eats no other type of onion, about once a month. At some point I decide to harvest the greens, storing extra in the fridge or freezer, and ditch the root ends, which after a while look unappealing. I change the water daily.