For healthy plant growth, each water garden container must be able to hold enough water to cover each plant to its preferred depth. For example, let's take an aquatic canna growing in a six inch tall nursery pot that prefers less than three inches of water over the crown. If it is set on the bottom of a 24 inch deep container, the plant will drown. If the same canna pot is set on some bricks or upside down pots so that it is raised up and the crown of the plant is near the water's surface, the plant will thrive.
The term water garden container encompasses the small pot that holds a single plant to a large one that holds many plants, fish, and fountains. The single plant pot is easy to create and maintain. If it holds an underwater plant or a floater, just fill it with water, add the plants, and you are done.
If it holds a shoreline plant, add some heavy clay soil, up to an inch of gravel on top to keep the mud in place, add the plant and water, and you are done. Don't use potting soil as many of the ingredients are too light and they will float, causing the water to always be a mess. If you don't have any clay soil, you can use generic kitty litter - it is made from clay. Do not use any that have deodorizing crystals or other ingredients.
Many aquatic plants look good all by themselves in a single pot. Dwarf lotus and water lilies can be planted in table top bowls. Larger specimens look nice in large oriental ceramic vases.
Larger pots can be planted just like the small one with several types of plants all growing together in the container. Large containers can also hold smaller pots to make a water garden arrangement that is easily changed as the plants grow or as the gardener decides to rearrange it. If the plants used prefer different depths of water, some can be set on pedestals to raise them to the proper level. Bricks, stones, and flower pots can all be used. Solid pedestal materials like bricks replace water volume, so if fish are being added, they will have less water available. Plastic pots will float and be difficult to use. Upside down clay pots often work very well.
A mix of container sizes and planting configurations can be used to make a flower pot arrangement on the patio. Just like with other patio pot arrangements use various sizes, shapes, and colors of containers to make your own personal style.
A mixed aquatic container can have the same style as many terrestrial potted arrangements; for example, a tall, spiky plant in the center or in the background, surrounded by showy flowers or brightly colored leaves, and as a final touch, plants that cascade over the edge of the container. Many aquatic plants have brightly colored foliage. Use them side by side for contrast and to attract attention.
Tall, spiky plants include cattail, yellow flag iris (Iris pseudacorus), sweet flag (Acorus calamus), rushes, papyrus, and canna. Broad-leaved plants include lotus, taro, arrowhead (Sagittaria), calla lily, and lizard tail. Flowering plants include water lilies and water bluebell. Cascading plants include parrot feather (Myriophyllum aquaticum), aquatic mint (Mentha aquatica), houtuynia, and water celery. If the container has enough surface water showing, then the addition of floating plants is always welcome. Add water lettuce, Pistia stratiotes, or water hyacinth, Eichhornia crassipes.
Many plants fit into more than one category. Don't crowd too many plants into a container. Aquatic plants are often very fast growers. If there is too much fertilizer in the water, the floaters will grow rapidly. It is easy to take a few out from time to time and toss them under some shrubs for fertilizer or add them to the compost pile.