A water garden can be an elaborate planting in and around a pond, or something simple in a watertight container.
A water garden opens up a new world of planting and landscaping possibilities. You can start small, with a hollowed-out stone that catches rainwater or jump right in with a half-acre pond that has water lilies, fish and a fountain.
Before building your water garden, do a little homework. Unlike regular gardening, where you can blunder your way through almost any experiment and start fresh the following year, a water garden usually involves a greater investment of time and money. Here's an overview of what's involved.
Siting and Design
A natural-looking water garden should have sloped sides with planting terraces that step down toward the deepest area of the pond. This allows you to plant a diversity of plant material and create different habitats. In northern areas, a depth of 24 to 36 inches is usually necessary to ensure that the pond will not freeze solid during the winter.
If you live in a warm climate, where frost heaving is not a problem, you can line the bottom of your pond with concrete, brick or even clay. Today, most gardeners and professional landscapers use a preformed liner made from fiberglass or plastic, or a flexible, cut-to-fit liner made from PVC or butyl rubber. The preformed liners are quicker to install, but the flexible liners allow for much greater creativity.
Where to Put a Water Garden
For something on a smaller scale, consider a patio water garden. Many water plants can be grown in a tub of water on your deck. Use an ordinary whiskey barrel lined with plastic, or purchase a plastic tub that is specially designed for a water garden. Put soil into the bottom of the container and plant right there, or submerge pots filled with the different kinds of water plants.
Water gardens can include floating plants, submerged plants and edge plants. Floating plants shade the water and absorb dissolved nutrients. By doing so, they help to suppress algae and keep the pond clean.
There are hundreds of varieties of hardy water lilies to choose from. Many bloom from late spring until frost and will survive the winter in ponds as far north as USDA zone 4, as long as their roots don't freeze solid. Plant them in sturdy containers that can be submerged 10 to 18 inches deep. Otherwise, remove the pots from the water in late fall and store in a protected area over the winter.
Tropical water lilies look similar to the hardy varieties, but the blooms are larger and more dramatic. Many are hardy only to Zone 10, and will not flower unless they are grown in full sun and are exposed to several weeks of temperatures over 80 degrees F. Some are day-bloomers and some are night-bloomers. Their roots are very delicate and can be easily damaged.
Lotuses are very dramatic. They raise their leaves and flowers 4 to 8 feet above the water, and the blossoms can be 10 to 12 inches across. After blooming, lotus flowers leave behind a large and distinctive seedpod. They are generally hardy to USDA zone 4 or 5 if their roots are not allowed to freeze solid.
Lotus roots are slow to get started, and they won't bloom without full sun and several weeks of temperatures in the 80s. However, once established, lotuses are vigorous growers and demand a lot of room. Under good conditions, one plant can spread 25 to 45 feet in a season unless grown in a container.
Submerged plants spend their entire lives growing beneath the surface of the water. They are usually called oxygenators. They obtain their nutrients from the water directly through their stems and leaves. By consuming nutrients, they help keep your garden from becoming a slimy green ooze by consuming dissolved nutrients. Submerged plants provide a spawning area and hiding place for fish and other water creatures. However, be careful, many are invasive and should be grown in containers. Common submerged plants include: anacharis, arrowhead, eelgrass and water milfoil.
Edge plants grow on a "shelf" that is 5 to 10 inches below the surface of the water or in the moist soil next to the pond, providing shelter for fish, frogs and other plant life. Shelf plants include sweet flag, water plantain, marsh marigold, pickerel rush, sedges, cattails and arrowhead.
Blazing Star Liatris is one of many plants that are good for moist sites.
Plants that can be planted in the moist soil next to a pond include filipendula, Japanese and Siberian iris, trollius, liatris and ajuga.
Fish can be a fun addition to a water garden and help keep the mosquito population in check. Plus, their wastes are a good source of nutrients for plants. The challenge is keeping the fish population under control. Too many fish means too many nutrients and that leads to algae blooms. As a general rule you can have no more than 1 fish per 3 square feet of surface area. (with an active filtration system and air pump, the number can be much higher.)
Most native fish (like guppies and mosquito fish) can survive the winter in the pond if the water doesn't freeze to the bottom. Keep a hole open in the ice to allow oxygen exchange.
Koi are the large colorful fish popular in Japan. Koi require highly oxygenated water, which means your pond needs a filter and air pump. They must also be fed daily and tend to eat water plants (especially expensive water lilies).
Once your new pond has settled in and the water quality has stabilized, frogs, toads, snails, clams and water insects, like water striders and dragonflies, will begin to appear. Each of these creatures will settle into its preferred habitat, helping to complete the ecosystem.
Learn about the science behind water quality. And be attentive to what is going on in that ecosystem. Water gardening is a dance with nature, and in this dance, nature always leads.
To avoid installing an active filtration system, maintain the right mix of water plants, be careful to remove dead or dying plant matter and tolerate water that isn't crystal clear. However, if your pond is stocked with fish, especially koi, you may need a filtration system to clean and oxygenate the water.