Is it okoay to cut back plants that have died off? I am in Pa, zone 6, and the stalks from my asiatic lilies, which stopped blooming in July, finally turned brown and withered over the past month. They are still very firm. I was going to cut them back, but a co-worker told me if I've gone this long without cutting them back then the bulbs may die before Spring. I'm green thumb-challenged so I wasn't sure if it was true.