To the uninitiated, water gardens seem complicated, expensive, and fussy. But they don't have to be, especially if you start small with a water garden in a container. Many of the principles of gardening in water are the same as those for gardening in soil. If you can grow a tomato, you can grow a water lily.
In your garden, you probably have shrubs, some flowering plants and vegetables, and a lawn. Think of water plants in the same way. Tall bog or border plants, such as marsh marigold (Caltha palustris), canna, sedge (Carex), taro (Colocasia esculenta), and cat tail (Typha), grow with their roots submerged and foliage above the water. As with shrubs in a terrestrial garden, their size and height add structure and provide a backdrop for flowering plants.
Submerged or oxygenating plants, such as fan wort (Cabomba), anacharis (Elodia or Eyeria), parrot's feather (Myriophyllum), and eel grass (Vallisneria), live underwater where they supply oxygen and compete with algae for nutrients. Floating plants like duckweed (Lemna) and water lettuce (Pistia) move freely across the water surface and provide algae-suppressing shade. Like turf grasses or mulch, they are not the stars of the show but are necessary to the landscape.
Keep in mind that some aquatic plants can be invasive and are prohibited in certain regions. Water lettuce and water spinach (Ipomoea aquatica) are prohibited in some states, including Texas, Florida, and South Carolina, and it is illegal to possess water hyacinth (Eichhornia) in many states. Though most mail-order companies will not ship to these areas, it is best to check with your cooperative extension office before ordering.
When you think of ornamental water gardens, exotic-looking water lily (Nymphaea) and lotus (Nelumbo) blooms and intriguing foliage probably first come to mind. Sedges, grasses, Japanese iris, and scores of other plants also add beauty.
Aquatic vegetables are less familiar in this culture, but they are dietary staples in many others. Aquatic crops that are well suited to small water gardens include taro, Chinese water chestnut (Eleocharis tuberosa), arrowhead (Sagittaria latifolia), and cat tail. (For others, see "Edible Water Plants" below.)
Most water plants grow in pots. Nursery pots like the ones perennials are sold in work well, or you can buy planting baskets made for water gardening. Line the pot or basket with two layers of newspaper to keep the soil from sifting out. In general, dwarf water lilies and submerged plants need pots about 6 inches in diameter and 6 inches deep. Most bog plants, full-sized lilies, and dwarf lotuses need pots at least 12 inches across and 6 inches deep. (Planting these in deeper pots is fine but not essential.)
Water plants need heavy, humus-rich soil like fertile garden soil or a good commercial topsoil or a water plant mix. Never use a potting soil that contains peat, perlite, or vermiculite because these ingredients float. After you pot your plant, cover the soil surface with a 1/2- to 1-inch layer of rinsed gravel to prevent fish from stirring up the soil.
Nearly any watertight container can hold an aquatic garden. Let your imagination guide you. Floating water lettuce or shallow-rooted watercress will live in a birdbath, and a clump of cat tails will be happy in a 5-gallon bucket. An old bathtub or livestock watering trough accommodates a full-sized water lily.
Keep in mind, though, that it is easier to maintain stable temperatures and ecological balance in large volumes of water, and that dark-colored containers can really heat up in the summer sun. Partially burying containers in soil or shading them keeps them cooler. Placing the pots where they will receive an hour or two of shade during the hottest part of the day also helps.
When choosing containers, select ones made of nontoxic material, such as untreated wood, plastic, glazed ceramic, or terra-cotta. Half barrels previously used to store liquor or food should be lined with PVC sheeting to prevent harmful residues from leaching into the water. Set a 5-foot-square liner into the tub, pleating it where necessary. Staple it into place around the top, and trim off the excess. Use liners to make leaky containers watertight, too.
Whenever you turn over fresh garden soil and plant a row of vegetable seeds, what comes up first? That's right--weeds. New water gardens are like that, too. At first, the water will probably get cloudy with suspended algae "weeds" and turn green. Don't panic! You don't need a filter or a degree in chemistry--just simple setup instructions and patience.
Select a site where the container will receive at least 6 hours of full sun in the morning or afternoon. Fill it with tap water, and let it sit for a day or two to dissipate the chorine and allow the water temperature to moderate before introducing plants.
There are many ways to create a tub garden and a multitude of plants and fish to select from, but for a thriving, low-maintenance container garden, the key is balance. Like any ecosystem, a healthy, self-sustaining water garden must contain a balance of essential elements. The Basic Tub Garden recipe below offers a simple formula for creating a successful container water garden that's suited to a broad range of climates. Before choosing more exotic or demanding plants and animals for your tub garden, consult local specialists or mail-order gardening sources.
If you get excited about water gardening, try grouping several containers. Plant space-hungry cat tail, lotus, arrowhead, or water hyacinth in decorative containers, and arrange them to display their different heights and textures. Stack containers of mixed plants at different levels, and install a circulating pump to create waterfalls.
Also use multiple containers to grow plants with different needs. Water lilies, for example, prefer warm, deep, still water, but watercress needs cool, shallow, circulating water. Group the tubs in a corner of your deck or make them the focal point of your patio. Add a few potted palms to complete your tranquil retreat.
Edible Water Plants: Seven Choices for Containers
* Violet-stemmed taro (Colocasia esculenta 'Fontanesia', sometimes sold as Xanthosoma violacea). Harvest tubers from dormant plants that have grown vigorously during the previous season. Steam, bake, or fry the starchy tubers, removing the fibrous brown skin before eating. When cooked, taro has a mild, nutty flavor.
* Chinese water chestnut (Eleocharis tuberosa). Harvest corms from dormant plants. Peel off the thick outer cover and slice the crisp, white flesh into salads and stir-fries.
* Water spinach (Ipomoea aquatica). Pick young shoots and leaves from this vigorous vine, and use as a green vegetable in Asian dishes or as a substitute for spinach.
* Common watercress (Nasturtium officinale). Pick bright green leaves and small shoots, and add them to salads and sandwiches for a peppery flavor.
* Yellow pond lily (Nuphar lutea). Dig roots during dormant season in fall or early spring; scrub and add to soups and stews. Dry seeds in warm oven, and remove the kernels. Boil lightly, and serve like corn.
* Arrowhead or duck potato (Sagittaria latifolia). Harvest starchy tubers in fall when the tops die and the plant is dormant. Peel and boil or bake like potatoes.
* Cat tail (Typha latifolia). Collect yellow pollen to use as flour. Gather young shoots, and slice them into salads, or boil for 15 minutes. The green flower spikes can also be boiled for 5 minutes and eaten. After the plants become dormant, dig the roots, and harvest the sprouts of next season's growth; boil for 10 minutes.
For a container water garden about the size of a half whiskey barrel (or for every square yard of water surface), you will need:
2 bunches of oxygenating or submerged plants
1 water lily or floating plants that will cover 60 to 70 percent of the surface
1 or 2 bog plants for height (optional)
2 trap-door water snails (Viviparus malleatus) to eat algae
2 or 3 mosquito fish, goldfish, or guppies (each 2 inches long) to eat insects
Fill the tub with water, and let it sit for a day or two. Place the potted oxygenating plants and water lily on the bottom of the tub. Set potted bog plants on inverted flowerpots or clean bricks so that the water level comes just above the soil line. Wait two to three weeks before adding fish.
Remove dead leaves and plant debris regularly, and replace water lost to evaporation, but don't change any water. Within a few weeks, the aquatic plants will starve the algae, and the water should clear. If it doesn't, add another pot of oxygenating plants.
Ann Whitman writes and gardens in Bolton, Vermont. Her most recent book is Organic Gardening For Dummies (Hungry Minds Inc., 2001; $17).
Article published on June 23, 2008.