Once a Sansevieria blooms, that particular growth, or clump, will never bloom again. It will, however, continue to live for many more years (all things being equal), and produce baby plants, or pups. In time, these pups will produce a flower of their own, and the cycle repeats. They DO NOT have to be root bound to flower. This is a complete fairy tale - the result of an observation with a faulty conclusion. Sansevieria bloom when they are ready to bloom - a condition promoted by a combination of good and sufficient light, nutrients, and water. It takes a lot of energy for a plant to bloom.