I'm having a 6 year old clump of black bamboo removed as it wasn't planted with a root barrier. There are a several large culms (20 feet high) which have come up about 10 feet away from the mother clump. These new culms are close to the roots of an old forsythia and are going to be difficult to remove. If the mother clump is removed, will the offshoot runners die off, or form a new clump? As lovely as it is, I want to be rid of it all.