Old Dog is spot on.
To add info from my own experience, though it seems that it's 'easier' to maintain the plant as it is, in the pot, it's also an issue down the road as the planting material around the roots decays and floats in the bowl/tank - it's not a food source that bottom feeders will eat and it doesn't seem to filter well. So you're left with this awful green, almost insulation like, material that causes harm to the fish inhabitants in one way or another.
Better to cut open the pot, gently pull the material from the roots, rinse them off VERY well, and plant the... plant deep under sand/gravel/rocks. You can weight them down with natural materials if needed.