Have Grown Strelitzia From Seeds.

Question

Replanted them in big black potting bags. Roots now start growing through the bottom of the potting bag into the soil. Must I cut back those roots? About three years old plants.

Answer 1

Here are two articles that will be helpful with your root pruning questions:
https://www.gardeningknowhow.com/houseplants/hpgen/prune-roots.htm
https://www.gardeningknowhow.com/ornamental/flowers/bop/transplanting-birds-of-paradise.htm