They will send out rhizome, and new stem form from that. Soon, you'll
have to thin them because they take over the pond. Flowers are for show.
I haven't seen any new stems from them.

John Bachman wrote:

We have two water hyacinths in our new pond and they seem to be doing
well. They have doubled in size and appear healthy but have not
bloomed yet. Will they propagate? If so, how?

TIA

John