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Cornell gardening resources Water Gardening
Ecogardening Factsheet #17, Fall 1997

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Gardening in water is a unique, exciting and surprisingly easy endeavor. Most backyard gardens are part of the larger ecosystem surrounding them, but the water garden is an entirely self-contained miniature ecosystem. In addition, the water garden will attract toads, frogs, bees, dragonflies and birds from the surrounding area.

The water gardener is a true ecogardener, for no other form of gardening incorporates as many ecological principles. This approach to gardening is also very educational, and young people in particular may enjoy, and learn a lot from, a water garden.

Water gardening is surprisingly easy - the hardest part is usually just digging the hole! If space is limited or digging a hole is not possible, then consider using half of a whiskey barrel. Regardless of the size of the pond, it should be located on relatively level ground away from trees as they will shed leaves which can foul the water.

Pond Construction

The larger the pond, the better buffered it will be against temperature extremes and fluctuations in gases and nutrients. Most typical in-ground water gardens with fish contain between 500 and 2,000 gallons. Smaller gardens may not be able to support fish during the winter. Contrary to popular belief, the depth of the pond needs to be only 24 to 30 inches to allow fish to overwinter.

The most important part of the pond is the liner. Preformed fiberglass liners are available in various shapes and sizes. These are placed into a hole and the soil is filled in around the liner. However, a more popular option is to excavate the pond in the desired shape and place in it a flexible liner. The best liner available is a 45 ml. thick EPDM rubber sheet. These liners cost several hundred dollars per 100 ft2, but their 50 year life provides a relatively good value. Swimming pool liners are not suitable for water gardens. Remember to size the liner to account for the sides of the pond, and any remainder that you want buried under edging.

Use a hose to outline the shape of your pond. Generally, an oval shape is more aesthetically pleasing than a rectangle. Dig the pond 30 in. deep, leaving a 12 in. ledge for bog plants. Slope the pond slightly from back to front to allow submerged, decayed material to move to one end. Cover the bottom of the pond with one or two inches of sand or other soft material to prevent a stone or sharp object from puncturing the liner.

Lay the flexible liner in the sun, black side up, for a hour to warm it. Move the liner over the hole and anchor the edges with stones. Begin filling the liner with water, allowing the liner to slowly fall into the excavation. Once the pond is full, trim back the excess liner and edge the pond with rocks or sod. If the water in the pond comes from a chlorinated source, allow it to set for a couple of days before adding plants. Inoculate the pond with a gallon of water from a natural pond to supply the necessary bacteria and other organisms that will aid in nutrient cycling.

Plants and Animals

A healthy, self-sustaining pond contains a mixture of plants, animals and bacteria including:

  • water-lilies (to shade the surface and prevent excessive algal growth)
  • submerged plants (to oxygenate the water and provide a habitat for fish)
  • fish (to keep the water clear and eat mosquito larvae)
  • snails (to recycle nutrients and help break down organic matter)
  • bacteria (to detoxify ammonium nitrogen and recycle nutrients)

In addition, bog plants (to add dimension and habitat), frogs and salamanders (to clean up debris) provide additional aesthetic value.

Plant into containers that are at least 6 in. deep and have perforations in the sides. Use regular garden soil, but after planting, cover the surface of the container with gravel to keep the soil contained. Use a sufficient number of plants to cover about 75% of the water surface with leaves. One water lily per 15 ft2 provides about the right amount of coverage. Set water lilies in the deeper water, and set bog plants on the ledge. Hardy lilies can overwinter in the pond in cold climates. Bog plants can be moved to deeper water for the winter to ensure their survival.

Introduce fish after the plants have started to grow. The bacteria that convert ammonium nitrogen (harmful) from fish waste to nitrate nitrogen (relatively harmless) establish slowly in a pond, so do not introduce lots of fish soon after filling.

Feed fish once a day, and only as much as they will consume in 5 minutes. Fish will cease feeding when the water turns cold. Fish can survive for weeks without supplemental food provided that the pond is teeming with life. Pet stores sell food specifically for pond fish. "Sinking" pellets are available so that fish will not be conditioned to come to the surface when a visitor approaches - this is important if you own a cat or if your property is frequented by raccoons.

Do not become alarmed if algal growth appears to be excessive shortly after filling the pond. This will subside when the water lilies begin to shade the surface. It is best to wait until this initial algal bloom is over before introducing fish. Do not drain the pond and refill it, or the algal bloom will happen again.

Specialty water garden suppliers offer complete packages that contain the correct numbers of plants and animals for ponds of different sizes.

Water Features

Fountains and waterfalls are popular features of water gardens. Both help to oxygenate the water, so they are especially good features for smaller ponds. Unfortunately, water lilies do not grow well near moving water, so locate any moving water at one end of the pond and not in the middle - unless the pond is large.

A pump is required to move water. They are available in two types: submersible and surface-mounted. The size of a pump and outlet are determined on the basis of how high the water must move, the volume of water to be moved per minute, and the required pressure (for fountains).

Pumps range in cost from $50 to $250. Do not select a pump that moves more water per hour than the volume of the pond - one that moves 25% of the pond's volume per hour is best if you have a filter. Use a ground-fault interrupter for any electrical wiring.

Filters generally are not required, except for very small ponds or ponds containing lots of fish. The two most common types of filters are sand and ultraviolet (UV). The UV filter kills bacteria that pass over a UV light, whereas the sand filter traps out sediment and relies on bacteria in the filter to detoxify impurities.

Some communities have regulations against ponds without fencing because of the danger that they pose for children. Also, neighborhood dogs love to cool off in shallow ponds on hot summer days. A grating can be placed just under the surface of the water to prevent a child from falling in or a dog from jumping in.

Maintenance

Spring and summer: Feed the fish and regularly remove dead plant material and leaves from the water surface and pump intake. Top off the pond if it becomes low. Remove filamentous algae. If algae are a problem, reduce feeding and increase shading. Use algacides only as a last resort.

Fall and winter: Maintain a small opening in the ice to allow methane and hydrogen sulfide (harmful) gases to escape and oxygen to enter. More fish die from poison gas accumulation under the ice than from cold temperatures. Use a heater to maintain a hole in the ice. Do not open a hole with a sledgehammer or damage will occur to the liner and the eardrums of the fish.

Once a year, preferably in September, clean organic matter from the bottom of the pond, cut and remove excessive root growth, and trim water lilies. Cover the pond with netting to catch fallen and blowing leaves during autumn.

Ponds provide endless enjoyment for their owners, from the fish which anxiously await feeding time, to the colorful blooms of the lilies, to the sounds of falling water and croaking frogs at night. Establishing and maintaining a water garden is a true ecogardening experience.

Plant List

Lillies:

  • Many species of Nymphea and Lotus (tropical)

Emergents:

  • arrowhead
  • blue water iris
  • cattail
  • yellow flag
  • sweet flag
  • pickerel weed
  • rushes

Submergents:

  • pondweed (Elodea)
  • water starwort
  • water celery
  • water milfoil
  • water crowfoot

Floating plants:

  • fairy moss
  • water hyacinth
  • duckweed
  • water chestnut

Prepared by:

Dr. Marvin Pritts, Department of Fruit and Vegetable Science, Cornell University, Ithaca, NY 14853





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Website design: Craig Cramer cdc25@cornell.edu

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