Being a water gardener for 4 years,... learned allot about plants as I see them as a huge part of the whole water gardening thing . I have grown over 70 types of pond plants and now with my small buisness, I often come across ponds where I need to clean them out and come across NIGHTMARES of overgrown water plants--- marginals seem to be the worst.
--- Just yesterday,... my workers attached a 4foot by 4foot rootball from a cat tail reed that was almost 16inches deep and thick !!! The small plants had grown over the years and had infused themselves together. Every rock and piece of gravel was ROOT SNATCHED by the plants. Took a small hatchet and ricip saw to slice the root mass into managable chunks and then pull out.
The lillies were bare root in the bottom of this aquascaped pond and same thing--- infused into 4inches of gravel.
The blue pickeral was a close 2nd to the lillies. ( cleaned a pond with nothing but blue pickeral earlier this year- FREAKEN NIGHTMARE ! Huge plants... HUGE rootsystems grown together.
**** my opinion--- keep them to pots. They often will grow just as well---often jumping the pots lip by the end of the season. You can then move them in the pots,,.. fertilize them in the pots, ready to give away potted up if need be.
I take plastic bags from the grocery store and block the holes on the bottom of the pot when planting. I use DECOMPOSTED cow manure 1/3 -1/3 sand- and top layer of gravel according to size of fish in pond to thwart them from digging in the pots( bigger gravel for bigger koi)