I have a large pond with many hardy lilies. For several years I had them in pots which I fertilized regularly. Two years ago I decided to remove most of the plants from their pots and set them directly in the bottom of the pond, hoping that they would derive nutrients from the muck. Many of the plants did well and continued to flower but some have only produced leaves. I would like to fertilize the non-producers but can't think of a clever way to get the fertilizer into the submerged plant. Any suggestions would be most welcome.