I've had this one in the pond a good 5 years now and still doesn't need dividing, or repotting.    In the fall I pull the pot out and shear off all the exposed roots, then put it back into the pond.

The root system helps to keep the pond water balanced and they provide good hidding places for the fish.

Starts blooming around mid-April, and continues for several weeks.  Once the flowering is finished I prune out all the spent flower stems.  Then the foliage takes over rather then wasting energy on seed production.   

Plant grows to around 12" high.

The rim of the pot  sits  1" or 2" below the water surface, which is ideal for wintering them over.  They do produce viable seeds that need to be sown on dampish soil right after harvesting but the usaul method of propagation is by division.  I have one that sprouted in a pot of dwarf bulrush, which I will need to transplant to its own pot in the next week or so.

Hardy to zones 1-3