Hardy Water Lilies: There are hundreds of varieties of hardy water lilies in existence, but for convenience they are often classified according to flower colour: red, pink, white, yellow, peach and changeable. Water lilies should be placed in approximately 2' (60 cm.) of water, depending upon the size of the variety. A heavy garden soil such as a clay loam provides a good planting media, but your lilies should also be fertilized regularly with an aquatic plant fertilizer throughout the growing season to ensure maximum flower production. Most water lilies require 8 hours of full sunlight in order to bloom well, but there are also low light varieties available that will bloom with only 3-4 hours of direct sun. In addition to the beauty that water lilies bring to the pond, they provide a practical purpose as well. The leaves of the lilies block sunlight from entering the pond and thus help to prevent an algae bloom.
Tropical Water Lilies: Tropical water lilies cannot be over-wintered outdoors in the Pacific Northwest, and must be removed from the pond by mid-October and stored in damp sand at approximately 10 Celsius (50 F.) until spring. The reward for this extra work is the phenomenal flower display produced by the tropicals. The colour range in tropical water lily varieties includes shades similar to the hardies, but in addition, there are many blue, purple, and even green flowering varieties of tropicals as well. Also, tropical water lilies are profuse bloomers and the flowers are often intensely fragrant.
Lotus (Nelumbo sp.): Lotuses, although winter hardy, are generally considered more difficult than other pond plants in the Pacific Northwest due to our cool, prolonged spring. You might call these plants the 'Rolls Royce' of pond plants, as the visual impact of a healthy, blooming Lotus is undeniable. In our climate, Lotuses are often grown in large tubs, which provide a warmer environment than deep, in-ground ponds.
Floating Annual Aquatics: Floating tropical plants such as water hyacinths and water lettuce are popular due not only to the visual interest that they add to the pond surface, but also for their ability to control algae (see 'Algae Control'). The floating roots of these plants are incredibly efficient at withdrawing nutrients from the pond water. These plants must be removed from the pond in late fall before they freeze and sink to the bottom.
Hardy Marginal Aquatics: This group of pond plants are commonly placed in shallow water close to the pond edge and can even be planted above the water line in damp ground. There are a wide variety of hardy marginals available, too many to list here, but some of the most popular include: Water Irises (large flowers), Cattails, Rushes, Reeds, and broad-leaf plants such as Pickerel Weed and Bogbean. There are also many smaller plants with colourful flowers, such as Marsh Marigold and Water Forget-Me-Not that are equally at home in shallow water or boggy areas.
Tropical Marginal Aquatics: These plants are indigenous to the tropics, but perform well in our climate providing that they are not placed in the pond too early. The water temperature of the pond should be approximately 15 Celsius, which may not occur until late May or even later in the Pacific Northwest. Cannas (specifically semi-aquatic varieties), Taros and Papyrus produce lush foliage and add a distinct 'tropical look' to the pond. Many pond-owners feel that the exotic, 'on vacation' impression that these plants contribute to the water garden is worth the extra effort.
Oxygenators: These plants, whether potted or free-floating, are placed deep enough to allow the foliage to remain totally submerged. The foliage does indeed release oxygen into the pond during the daylight hours, but the primary function of oxygenators in the pond is to remove excess nutrients and to provide a spawning area for fish. Baby fish (fry) also appreciate the presence of Oxygenators as it provides them with a place to hide from larger fish and predators. Popular varieties are: Hornwort, Elodea, Mare's Tail, and Parrot's Feather.
Pond Location: Choosing a site for your pond is the most important decision that you will make when planning a water garden. Although a shady location may help to prevent algae problems, it will also severely limit the variety of aquatic plants that will grow in your pond, as the majority of pond plants prefer full sun. We recommend installing the pond in as sunny a location as possible.
Algae Control: Algae problems in the pond are usually caused by one or both of the following conditions: (1) excess nutrients and (2) too much sunlight entering the pond. Algae, which is a simple plant, requires both food and sunlight in order to flourish. Nutrients in the form of Nitrates and Phosphates enter the pond through various means, the most common being the presence of fish. Although there are hundreds of algae species, as pond owners, we are usually only concerned with two types of algae:(1) microscopic planktonic algae which causes the pond to turn green and take on a 'pea soup' appearance, and (2) blanket weed algae which appears as long green strands growing on rocks or plants in the pond. Floating plants and oxygenators will remove the nutrients from the pond and help to starve the algae out of existence. Water lily pads and floating plants will also block sunlight from reaching the algae. The general rule is that there should only be a maximum of 40% open water if the pond is situated in a sunny location. In other words, by mid-summer, you should have 60% of your pond surface covered by plants.

Jack Wootton