How can you transplant water plants that is rootbound in the pot it was purchased in?
Answers:
You can't. It's impossible. It'll never work. You're DOOMED.
Other answers:
My pond plants get rootbound every few years. I usually cut all the roots off with a sharp knife, use tin snips or other heavy duty clippers to get the pot off. I cut back the plant roots by 2/3 and repot in pea gravel or other gravel. I don't use soil at all for the plants. Unless I'm trying to get bigger plants, I just replant in the same size pot.
I have lots of fish in my pond, so the 'plant food' is taken care of.
My pond plants get rootbound every few years. I usually cut all the roots off with a sharp knife, use tin snips or other heavy duty clippers to get the pot off. I cut back the plant roots by 2/3 and repot in pea gravel or other gravel. I don't use soil at all for the plants. Unless I'm trying to get bigger plants, I just replant in the same size pot.
I have lots of fish in my pond, so the 'plant food' is taken care of.
If a plant is root bound you just pull til it comes out. Then try to finger comb the roots out and trim them an inch or two. Then repot. As far as water plants, if they came out of water I imagine they will have to go back in. Call a local nursery.
Drill holes twice the size of the roots biggest size in the 'pot' all over and then re-plant the entire 'pot'.....but make many holes so that the root will expand outwardly......'it's' that easy....
Our pond is small (4' x 8' x 24 "). We gave up on re-potting our lotus plant. We just put it in the bottom of the pond and about once a year we pull it up and cut about a 1/3 off and drop it back in the pond. Seems like you just can't kill it.