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Put a Free Form Garden Pond in Your Backyard

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BLACK+DECKER B+D Contributor 193 Projects

If your idea of a water garden is more elaborate than most or the shape you have in mind isn't standard round or kidney, a free-form water garden with a soft, pliable pond liner may be the answer for you.

Building a water garden with a soft liner is not difficult or time consuming, but the finished garden will required on going maintenance and care. Think carefully about your willingness and ability to provide this care before committing yourself to the project. It’s also a good idea to look into local building codes—many municipalities require building permits for ponds over 18 inches deep.

Before selecting a flexible liner, compare and contrast the available types. PVC (polyvinyl chloride) liners are made from a type of synthetic vinyl that’s flexible and stable as long as it does not get direct sunlight exposure. If you choose one, make sure it is not manufactured for swimming pools or roofing.

EDPM (ethylene propylene diene monomer) liners are made from a synthetic rubber that is highly flexible, extremely durable, and fish-friendly. EDPM liners remain flexible at temperatures ranging from -40 to 175° Fahrenheit. These are cost-effective and easy to find at building or garden centers or landscape supply stores. Look for a liner that is 45 mil thick. Some landscape supply centers carry pond liner by the lineal foot. 

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Free-form ponds blend into the landscape, especially with the addition of coping stones set into the edges. Building one involves heavy labor, but no special skills.


Instructions

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    Flexible liners adapt to nearly any shape or size pond you want. They can fit a typical kidney-shaped excavation with planting shelves, like the one shown here, or a very unique shape of your own design. EPDM rubber liner material is sold in precut sizes at your local home and garden center.

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    Select a location well away from buried utility lines. Use a garden hose or a rope to outline the pond. Avoid very sharp turns, and try for a natural looking configuration. When you’re satisfied with the pond’s shape, lift the hose or rope and use spray paint to mark the perimeter.

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    Find the lowest point on the perimeter and flag it for reference as the elevation benchmark. This represents the top of the pond’s water-holding capacity, so all depth measurements should be taken from this point. Start digging at the deepest point (usually the middle of the pond) and work out toward the edges. For border plantings, establish one 6- to 8"-wide ledge about 12" down from the benchmark.

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    Set a level on the plant shelf to confirm that it is the same elevation throughout. Unless your building site is perfectly level or you have done a lot of earth moving, the edges of the pond are not likely to be at the same elevation, so there may be some pond liner visible between the benchmark and the high point. This can usually be concealed with plants, rocks, or by overhanging your coping more in high areas.

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    Dig a 4"-deep by 12"-wide frame around the top of the hole to make room for the coping stones (adjust the width if you are using larger stones). Remove any rocks, debris, roots, or anything sharp in the hole, and add a 2" layer of sand to cover the bottom of the frame.

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    Cover the bottom and sides of the excavation with pond underlayment. Pond underlayment is a shock-absorbing, woven fabric that you should be able to buy from the same source that provides your liner. If necessary, cut triangles of underlayment and fit them together, overlapping pieces as necessary to cover the contours. This is not a waterproof layer.

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    Lay out the liner material and let it warm in the sun for an hour or two. Arrange the liner to cover the excavation, folding and overlapping as necessary. Place rocks around the edges to keep it from sliding into the hole.

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    Begin filling the pond with water. Watch the liner as the water level gets higher, and adjust and tuck it to minimize sharp folds and empty pockets.

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    Add some larger stones to the pond as the water rises, including a flat stone for your pond pump/filter. If the pump/filter has a fountain feature, locate it near the center. If not, locate it near the edge in an easy-to-reach spot.

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    Fill the pond all the way to the top until it overflows at the benchmark. Remove the stones holding the liner in place and begin laying flat stones, such as flagstones, around the perimeter of the pond. Cut and trim flagstones as necessary to minimize gaps.

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    Finish laying the coping stones and fill in gaps with cutoff and shards. If you are in a temperate climate, consider mortaring the coping stones, but be very careful to keep wet mortar out of the water: it kills plants and damages pump/filters. Set flagstone pavers on the ledge at the perimeter of the pond. Add more water and adjust the liner again. Fill the pond to just below the flagstones, and trim the liner.

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    Consult a garden center, an extension agent from a local university, or the Internet to help you choose plants for your pond. Include a mixture of deep-water plants, marginals, oxygenators, and floating plants. Place the plants in the pond. If necessary to bring them to the right height, set the plants on bricks or flat stones. Spread decorative gravel, sand, or mulch to cover the liner at the perimeter of the pond. Install plants along the pond’s margins, if desired.

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