Any good gardener, which is not me, will tell you that the best way to keep a garden healthy and thriving is to prune back the plants. They say you have to remove the older growth so that the young, fresh growth has a chance to thrive.
In my fish tank, the old leaves were taking all the nutrients out of the plant in an attempt to stay healthy, and that was preventing the new growth from establishing itself. It was also unbalancing the health of the tank overall, by disrupting the water quality that everything relies upon to survive, fish and plants both.