Well, There are problems with this nothing can survive without Energy for too long and plants use photosynthesis which requires water and Carbon dioxide, there is no known way to keep something alive without energy, so a pro tip if you want to keep a plant alive without it being rooted in the ground is keep it well hydrated and in a well lit area with the type of color that its chloroplasts uses, but there is no way to keep them alive forever by this method unless you go hydroponic.

Now, as I say that, there is some genetic engineering that could be done to make it store more energy and such as to not die as fast, but that will take some doing, I do have some ideas but I live in the state of Indiana. It depends how much money do you have to spend given enough, we could definitely do something completely unnatural to keep them alive for longer. *puts on his mad science glasses*, which means completely untested.
