There are many types of pond plants you can choose for your water garden. They can be grouped into four main categories: water lilies, floaters, oxygenators, and marginals.
Water lilies provide shade, shelter, and a natural environment for fish, frogs, and other small creatures living in your pond. Most water lilies, when purchased from a garden center or big box store, are sold as a bare tuber that's been dry-potted in a regular 10" landscape pot. They basically resemble a turnip with some thin, stringy roots and a few dried stubs of stems poking out the top. Lilies are packaged like that because it's a stable way to transport them around the country, but it is not intended to be a long-term home for the plants. That kind of plastic pot is much too narrow for a plant like the water lily, whose roots spread out horizontally like a carpet. They can still survive in such a container, but their growth will become stunted, limiting the number of flowers the plant will produce.
For the best results, we recommend potting your lily in the largest pot possible. We like to use the fabric lily pots from Aquascape that are 7" tall and 14" in diameter. They have a cinch top that is useful for containing the soil, and the flexible shape works well to conform to uneven rocks at the bottom of the pond.
Start by adding about 3"-4" of specially-formulated planting media to the fabric pot. Once that is done, it's the perfect time to add some fertilizer. We use two types: quick-release tablets and once-a-year pellets. This provides the plants an immediate source of nutrients for establishing itself in its new home, and a sustained source of nutrients that will keep it well-nourished throughout the year. After adding the fertilizer, we like to cover it up with a little more soil; another 1/2" to 1" will suffice to protect the plant roots from direct contact with the fertilizer and encourage root growth.
A nice trick when potting marginals is to place a smaller plant towards the edge of the pot with the taller plant in the center. This creates a cascading effect and will soften the edges of the pot, better blending it in with the rest of your water garden.
If you are planting a hardy lily, place the tuber at the edge of the pot, angled towards the center with the spiky, growing end pointing upwards.
At this point you can add spread small rocks or pea-gravel atop the soil in the pot to protect the soil from fish and help contain it within the pot.
Now you are ready to place the freshly potted plant in the pond. Gently lower the pot into the water at a slight angle, so the rush of water doesn't displace a bunch of soil and cloud the pond. The optimal depth in which to place your potted water lilies is 10" to 18". Too shallow and the stems will stick out of the water, attracting aphids that the fish would otherwise eat and keep under control. Too deep, and the pads will struggle to reach the surface, nor will you see many flowers. Don't worry if the lily pads do not reach the surface at first, they will quickly grow towards the light.
Floating plants are simply placed in the water wherever you'd like them. They require no potting, as their roots take in nutrients directly from the water. These plants are fun and easy to keep, and can be a nice food source for fish, turtles, and birds. They grow so well that they may need to be thinned out occasionally. Just be careful in case you happen to have one of the few invasive species of floating plants that is banned in NJ: Eurasian water milfoil, hydrilla, and water chestnut. If you do have one of those species, they must be destroyed when they are removed to prevent the potential spread to natural waterways.