With the Island Living Expansion Pack, you can go in build mode and put these plants in the water. They will still be fully functional. I will note that I had to put them in a line in order for them to be at a good height compared to the water.









With the new pond tool my plants can be placed in them
while using the BB.MoveObjects cheat.
Choose an area of the pond to make shallow enough for sims to enter the pond,
but deep enough to put the plant in.
Place grown plants in the pond and use the Shift+CTRL+9 Key
to raise them to the water level.
It's not easy to do the first plant, but if you play with it you can get it right.