Plants for Water Gardens
By Dr. Leonard Perry, Extension Professor
University of Vermont
Tired of the same old kind of gardening? Or, have you recently added a pond or small pool to your garden to add beauty and tranquility? In either case, including aquatic plants adds a new dimension to your gardening.
Mention aquatic plants, and most people first think of water lilies. These come in basically two kinds--the hardy species and cultivars and the tropical water lilies. The tropical ones can further be divided into day and night bloomers. Even though the first group is termed "hardy," meaning they will live below ice in large ponds, the plants will not withstand being frozen so must be brought indoors for winter.
The common pond water lily found in the North is the fragrant pond lily (Nymphaea odorata). The white flowers, with their floating green leaves and upcurved petals span up to four inches across. A variety of this, the dwarf pond lily (Nymphaea odorata var. minor) has smaller leaves and flowers. Some hybrids of this species are 'Aurora' with yellow flowers that turn red with age; 'Helen Fowler' with fragrant, four- to six-inch pink, flowers; and 'Yellow Pigmy' with three-inch yellow flowers.
Other hardy hybrids of water lilies include the marliacea species with white flowers flushed pink (var. albida), canary yellow (var. chromatella), and pink to coral red with bronze leaves (var. rosea). 'Attraction' is a popular water lily with garnet red flowers; 'Commanche' has purple leaves when young and rose to apricot flowers; 'Helvola' has yellow flowers and leaves blotched brown; and 'Pink Sensation' has fragrant pink flowers held above the water.
'Helvola' is useful for small ponds or tub gardens, as it will grow in a two-gallon pot and cover only one to six square feet of water surface. When buying or ordering water lilies, make sure they will fit in your water garden. Moderate growers spread six to 12 square feet, and large vigorous ones spread over 12 square feet. Keeping plants in pots will keep them smaller. Planting them in soil on a pond bottom will encourage more growth.
Tropical water lilies definitely won't withstand cold water. Day-blooming cultivars include the purple 'Mrs. M.E. Randig,' the blue 'Henry Shaw,' and 'Mrs. Edwards Whitaker.' The lavender-blue flowers of the latter age to a silvery blue. Night-blooming cultivars include red and pink cultivars, which need to be lighted with flood lamps or other lighting to see well. White-flowered night-bloomers are attractive in dim light and include 'Sir Galahad,' 'Missouri,' and 'Wood's White Knight.'
Of the many other types of plants for water gardens, the oxygenating plants take up carbon dioxide and give off oxygen. This is important if you also have fish in the pond. These plants take up excess nutrients from the water, which in turn keeps down algae growth. Examples of these include Pond Weed (Elodea), Parrot's Feather (Myriophyllum), and Arrowhead (Sagittaria).
Some of these oxygenating plants, such as the Canadian pond weed, and other perennials such as the Purple Loosestrife, may be invasive either by seeds or roots. Make sure you do not use such invasive plants if natural water bodies are nearby.
Emergent or marginal plants are those that grow in shallow water no more than two to six inches deep. The most familiar of these are the cattails (Typha species) often found growing in natural areas or wet areas along roads several feet tall. There is a dwarf species that only reaches about two feet high (Typha minima). Other marginal plants include the Yellow Flag iris (Iris pseudacorus), the Blue Flag iris (Iris versicolor), Pickerel Rush (Pontederia cordata), and Marsh Marigold (Caltha palustris).
Many hardy ferns do well in pond margins, including the large Ostrich Fern (Matteucia) and the smaller Lady Fern (Athyrium). Many grasses, sedges and rushes add fine textures to water gardens. Some of these include the rushes (Carex) and Ribbon Grass (Phalaris).
Other plants merely float, their roots dangling in the water to absorb nutrients and provide homes for fishes. By absorbing nutrients, they are useful for controlling algae that grows on excess nutrients in the water.
Many of these floaters are tropical so need to be floated indoors in water over winter. And many are invasive, so keep them away from natural bodies of water. They are useful to cover water surfaces until the slower growing water lilies can cover the surface.
Floating plants include the water lettuce (Pistia stratiotes), which looks like small floating heads of lettuce. The water hyacinth (Eichhornia crassipes) has beautiful blue, hyacinth-like flowers with air-filled bubbles for stems that help it float. This plant clogs waterways in Florida and so is banned from interstate sales there. The Fairy Water Lily (Nymphoides aquatica) has small water flowers and kidney-shaped, four-inch leaves.
But whatever plants you favor, be sure to select healthy specimens with no signs of disease or rot. Your local garden center should have many of the species listed above or can give you suggestions for other plants suitable for your area.