If you want to keep the plant, just say for plant clippings or to use as deco, yes you do turn it to decorative and it will pop into your back pack.
Just say you grew plants for seeds or orange petals, and you have already plucked them all, and do not want plant clippings from them, then you click on the little pile of dirt looking icon on bottom right side of plant gump, to "abandon the plot". The spot where the plant was goes empty and the plant just disappears.
If you grew a plant, that has resources on it say, poppies dust, and you want to keep it alive and store the whole plant in a secured container to keep from having to care for it more, and to save on room (from all the plucked dust) ... I don't know the answer to that one. I have not needed to try it yet.
Hope one of the top two answers helped ya out.
