Lily pads have enchanted gardeners long before Charles Monet painted his famous water lilies scenes. These plants bring to mind dragon flies, and frogs perched on the floating 'lily pad' leaves. In the wild, water lilies can quickly become invasive. But their appeal is such that they are frequently sold in garden centers for container planting in ponds.
Water lilies are classified in two groups. These are hardy lilies and tender or tropical lilies. Hardy lilies will survive outdoors even if the water on a pond's surface freezes into a thick sheet of ice. Some hardy lilies have even been found growing wild in Alaska. Many water gardeners overwinter hardy bulbs by removing foliage from them and moving the plants to the deepest part of a pond. Tropical water lilies will not survive outdoors in a garden pond under these conditions. Gardeners who wish to grow tropical bulbs must remove them from a garden pond once temperatures begin to cool. During winter months, Tropical lilies can be placed in damp sand in a bucket and left in a warm, dark location throughout the winter months.
Water lilies are known as marginal water plants because they grow in the wet soil at the margins of a pond. Water lilies that grow in the wild can become invasive because they have an unlimited amount of soil in which they can divide and spread. By contrast, lilies that grow in water gardens are typically placed in containers to keep them under control. Hardy bulbs grow from rhizomes, while tropical bulbs grow from crowns. Both types of lily bulb must be planted with their tip above the soil line.
The purpose of the lily's pad is to collect light for the plant to use in the process of photosynthesis. The tubers cannot collect light in the depths of the water. Instead they send up leaves on a flat stalk. These 'lily pad' leaves are an adaptation to the plant's environment. They are wide and flat to distribute weight evenly so that the leaf will float well. Both types of lily will not grow well in water deeper than 6 to 18 inches deep.