Delicate Balance

Most aquatic gardens host at least a few water lilies, common pond plants known for their floating heart-shaped leaves and multi-petaled, pearl-, eggshell-, lemon- or blush-colored flowers that glide above the surface like dancers swathed in silk scarves.

Spring fertilization can enhance water lilies’ beauty by ensuring blooms. Photo: AquaScape Designs.

Yet water lilies are only a fraction of the pond plant bounty. Among them is an enticing treasure trove of water blossoms, each with their own purpose in the garden. Planning a water garden is a lot like designing a traditional flower border – plants are chosen based on how they complement each other in color, height and bloom time. But just as each member of a flying trapeze team must master precision or risk upsetting the balance of a high-flying stunt, each pond plant has a specific chore that ensures a stable, thriving ecosystem.

VISION & VARIETY. Aquatic plants are necessary pieces in the pond puzzle. They provide natural cover and oxygen for fish and add beauty, pointed out Elaine Hinson, sales representative, Sparkle Water Features, Beaufort, S.C. “Without aquatic plants, an ecosystem cannot function properly,” she stressed. “Aquatic plants take their nutrients from the water, not the soil. They feed on nutrients provided by aquatic animals and compete with algae for food.

Without aquatic plants, Mother Nature plants algae in a pond. Enough aquatic plants will naturally minimize the availability of food for algae and starve it out.” To balance a pond, aquatic plant material should cover nearly 50 percent of the pond’s surface, suggested Bonnie Hale, plant expert, KoiVet.com. There are four common pond plant categories: lilies, floaters, marginals and oxygenators. “Each enhance a pond’s beauty as well as contribute to its environmental balance,” Hinson said.

Hardy and tropical water lilies with their colorful blooms and broad leaves are a pond’s crown jewels because they are noticeable and assume daily duties. “Lilies have broad leaves that provide shade from the sun’s heat to help cool the water, and they offer fish a welcome retreat from predators,” Hinson stated. Hardy water lilies are perennial and can be planted from zone 3’s northern reaches to zone 11’s subtropical, southern areas. “In the winter, hardy water lily foliage dies back and retreats to the pond’s bottom, but new shoots arise from their embedded rhizomes in the spring,” Hinson said. “After the first frost, cut off the stems a couple of inches above the base and let the rhizomes have a long winter’s rest.”

Tropical water lilies are more colorful, ranging from basic shades of white and yellow to vibrant lilacs, copper-oranges and scarlets. “And some of them bloom at night instead of just during the day,” pointed out Wes Herring, partner, Quality Ponds, Columbus, N.J. But tropical lilies only winter over in zones 8 through 11, so they are treated as annuals in northern U.S. regions, Hinson said. No matter the zone, all contractors agree that spring fertilization ensures flowering and enhances most lilies’ beauty.

Marginal plants, also known as bog plants, grow on the shallow margins around a pond’s edge and are native to temperate regions. “They provide a smooth transition between terrestrial plants surrounding the pond and aquatic plants,” Hinson said, adding that they also provide color, foliage and bloom variation. Some examples of aquatic marginals are sweet flag, with iris-like leaves and tiny green flowers; cattail, known for its erect, tight seed head that resembles a cat’s tail; sedge, with long, narrow leaves and inconspicuous flowers in shades of green and white; and arrowhead, which has arrow-shaped leaves.

Tropical marginal plants, like parrot’s feather with pink stems clothed in bright green feathery foliage, are not perennial in regions that experience winter frosts and freezes. Besides framing the pond, marginals provide shelter from wind and shade and remove excess nutrients from the water that might otherwise feed algae, Herring said. If the water garden is in an area of the country that experiences winter conditions, Rich Damko, president, Landscape Professionals, Chesterland, Ohio, suggested contractors cut back marginal plants to just above the water’s surface in the fall.

Floater plants are placed on the water’s surface to float around, Damko said. The foliage of tropical floater plants like water hyacinth with round, fleshy-leaved rosettes and blue-purple flower spikes, and water lettuce, which has 6-inch-wide leaf clusters resembling lettuce heads, rests above the water while their roots dangle below the surface. “[Floater plants’] roots hang freely providing small fish with a place to hide,” Herring said. “The long roots also draw nutrients from the water while they collect floating debris that would otherwise become algae food.”

While floaters benefit a water garden, they also can multiply rapidly and two or three of them in full sun can completely cover the surface of a pond in weeks, Herring warned, adding that to control them contractors need to thin them out regularly. Some floaters like fairy moss, which looks like a rich, green carpet of tiny flowers and turns pinkish-red in cool weather, spread rapidly and will become too aggressive unless koi can snack on them and knock back their vigorous growth, Hinson advised.

In the winter, floaters need to be removed from the pond and replaced each spring since they are annuals and will not survive the colder temperatures. Many contractors recommend oxygenators for a well-balanced pond. Their roots and leaves live underwater and, like sponges, they absorb carbon dioxide and minerals and help starve algae, Hinson said. Common oxygenators include Canadian pondweed, which has small dark green leaves that blanket brittle stems, and hornwort, with slightly brittle, mid- to dark green foliage. Hardy oxygenators tolerate warm water, but become frail in hot climates.

But Paul Holdeman warned contractors of oxygenators’ nature to dominate a pond. “They are thick underwater shrubs that pull in nutrients like the coral reef,” explained Holdeman, owner, The Garden Gnome, Peoria, Ariz. “They pull food from the water so they keep it clean, but they can take over. That’s why having fish is important. Koi love to eat these plants and these plants provide good cover for the fish.”

As with traditional garden plants, the-right-plant-in-the-right-place rule applies to ponds. Plants should be chosen based on pond location and size, and fish type and size. For example, as koi grow, they tend to enjoy tearing at pond plants, Herring said. “So, put sturdy and tough-rooted plants in the pond, like rushes and irises, if you have large koi – or plan to,” he said. “Don’t use water lilies and plants that are fragile and easy to rip apart.” In terms of cost, aquatic plant prices vary from a few dollars for floater plants to up to $40 for some water lilies in Ohio, Damko said. According to Herring, in New Jersey they range from $5 to $7 for small plants to $25 to $35 for potted lilies.

PLANTING POINTERS. Contractors use various foliage installation methods based on the flora’s characteristics and whether clients have concrete- or rubber-lined ponds. In rubber-lined ponds, contractors should include plant pockets in the liner and add enough gravel as a base to install some marginal water plants around the perimeter of clients’ ponds and cover the entire liner base for a natural look, Damko suggested. Herring agreed, advising contractors to install marginal plants in one-third of the pond’s circumference.

But since they grow tall, Herring recommended contractors plant these in the back of clients’ ponds so their view isn’t blocked. Since marginals are shallow, the pond water should be no more than 2 inches over the soil of the pot, Herring said. Marginals should be planted in gravel because their roots can take nutrients from the substrate where fish waste and other organic debris settles, Hinson said, suggesting contractors plant them in no more than 2 inches of gravel with a few rocks around them to provide support until the roots take hold.

 “Avoid planting marginals in pots,” Hinson stressed. “Since their job is to filter the water and keep algae under control, they will take root in the gravel, extend their roots out horizontally and do a much more efficient job of filtration than if they were in pots. In addition, koi just love to root around in pots and turn them over.” For oxygenators, the type of material will determine the planting method. Many oxygenators, like hornwort, do not root and need to be anchored to the pond base with a stone or small lead weight, Holdeman said.

In terms of planting, water lilies have the most options and need the most care. “Since they have a greedy root system, it is important to plant water lilies in a large container with a soil depth of 6 inches or more,” advised James Allison in his book Water in the Garden. “Start containers off with support underneath so that there is only 6 to 10 inches of water over the crown. As the leaves reach the surface, lower the plant slowly into very deep water – 3 feet or more. Lowering a lily too rapidly will cap growth, resulting in small leaves, poor flowering or even death.”

This container method is used mostly in concrete-lined ponds or in rubber-lined ponds until the lily can be lowered to the pond’s natural depth. In rubber-lined ponds, dig lily pickets in the ground under the liner, punch the liner into the pockets, add some soil, the lily and about 3 to 4 inches of gravel, Hinson described. This planting method ensures growth room for plants and prevents them from becoming root-bound, Holdeman said.

Depending upon the climate and the amount of sunlight, hardy and tropical lily blooms should start to appear in early or mid-summer (at temperatures more than 65 F), Allison stated. Lotus, which is considered a lily-like aquatic, is the only plant Hinson recommends contractors install in a container in a rubber-lined pond because of its aggressive nature.

The author is Managing Editor of Lawn & Landscape magazine and can be reached at nwisniewski@gie.net.