Potted plants are an important part of a water garden. Lilies are usually the main attraction in the pond, and care should be taken in planting them. Lilies have a greedy root system that expands rapidly. Use the largest suitable container of 6 inches or more in depth. Plant hardy lily rhizomes with growing point or crown at soil level, exposed to water. The rhizome should be on a slight angle and the crown should be up and as far away from the wall of the container as possible. The plant will grow in the direction of the crown points and ample room for growth should be provided. This will also increase the time between re-plantings. If you intend on keeping the lily in deep water, start it out in shallow water. As the plant becomes established, move it a little deeper. Continue this process until the desired depth is attained. Planting a lily too deep too soon can stunt growth resulting in small leaves, poor flowering, and even death.
Tropical lily tubers differ from hardy tubers in that the tuber is rounded and produces leaves and flowers from the center rather than an end. They should be planted in the middle of the container with the crown slightly exposed. Tropical plants require water temperatures of 65 degrees or higher for vigorous growth. These lilies will not survive cold winters and should be protected from freezing in Zone 7 and higher.
For most pond plants, especially for water lilies and lotus, use a heavy, clay-based loam or topsoil mixed with a bit of sand, ensuring it doesn't contain compost or peat, which can float and foul the water. For bog plants and some other aquatic plants, a poor, acidic, or even just pea gravel can work, as the nutrients are absorbed from the water. Avoid standard potting soil, as it will float, and opt for a nutrient-rich planting media specifically for aquatic plants.
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