Roots will take easilty....seeds work too. they spread like wildfire where I have tried (wetareas, not standing water though)....get the seed pods and disperse them, simple as that. Having lots of mud helps as opposed to hard bottom (gravel/rock).
I don't think you will have a problem getting them to establish. I have a cattail swamp about 50 yds from my new pond, and its a constant battle keeping them out. I think the seed just keeps blowing in. Let me know if you need some seed heads.