Gardening Articles: Landscaping :: Container Gardening & Ponds

Building a Water Garden

by National Gardening Association Editors

If you've decided to install a pond or water garden, you need to decide which kind you would like and how much you want to spend. Excavated ponds with concrete linings are very expensive and require professional installation. Flexible pond liners are less expensive, and you can do it yourself if lots of digging and lifting aren't a problem for you. (Some manufacturers sell liner material in sheets or convenient rolls, and some liners with a prebonded geotextile underlay.)

Another option-though one that also requires digging on your part-is to install a preformed in-ground fiberglass or inexpensive plastic pond unit (some can also be installed above ground). Besides cost and effort, there is another consideration: life span of the materials. Concrete lasts longest, except perhaps in areas of heavy shifting of frozen earth in winter. Flexible liners of EPDM, butyl rubber, or PVC (some are tear-resistant) last about 20 to 50 years. And plastic preformed units last only about 3 to 5 years.

Once you've decided which style you'll install, the next step is to map out the dimensions. The following instructions assume a finished pool size of 10 feet by 7 feet constructed with either a flexible liner or preformed 12-foot pond unit.

Step 1. Mark the outline. Use rope, stakes and twin, or sand to mark the outlines of the water garden you plan to install. Next, remove the sod to a depth of 2 inches and about 12 inches in width around the edge of the pond. Use a carpenter's level across the opening to determine whether the ground around the edges of the pond is even.

Step 2. Excavate. Use a round-point spade or mini-tiller to dig up the water garden area in two stages: dig a shelf on the far side (from viewpoint) that's 12 inches deep and 12 to 15 inches wide. Mark an inner pool with sand or string to indicate the deepest part of the pool, which must be deep enough for water lilies to root in mud that won't freeze: at least 18 inches.

Step 3. If you plan to include marginal plantings or a waterfall, dig down to two different depths (or tiers). Line the bottom of the hole with soft sand. Then, if your liner material doesn't have a bonded underlayer, lay a separate underlay or carpet or geotextile or polyethylene mat before placing the rubber liner over the surface of the pond floor.

Step 4. Next anchor the liner's edges over the banks of the pond with stones or other heavy edging material. Adjust the liner bottom, and fill the pond slowly with water, gradually pleating the large creases to stay flat, and adjusting the stones for the liner to settle. For a preformed pond unit, make the area slightly larger and deeper than the pond unit. Shovel the soil out well away from the edge so it can't sink back in easily. After you've marked and dug the area, set the preformed pond liner in the hole and press it gently into the sand to seat it. Fill any gaps between the hole and the liner firmly with soil. No need to anchor the liner; the water will do that. Fill slowly and check levels to ensure that the pond water is evenly distributed and the unit isn't distorted; backfill as necessary.

Step 5. Arrange stones around the edges of your pond, and trim any visible lining material. After placing aquatic plants, add border plants and shrubs around the perimeter to create a lush transition to the rest of your landscape.

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