A pond can add color and life to any landscape, and it’s a weekend project that anyone can complete.
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Installing a liner requires four basic steps: digging the hole, laying down the liner, filling the pond with water and adding stones or other edging around the pond perimeter.
Use a flat shovel to remove patches or strips of sod within the pond area. Remember to remove the grass 6 to 12 inches beyond the perimeter so you'll have a flat surface.
Starting along the edge, dig out the edging to a depth of 9 to 12 inches. Then remove all dirt within the pond area by layers, digging from the center outwards. Dig 2 inches deeper than the pool depth to allow for sand underlayment (less for other materials). Create a spot to overwinter plants and fish. In cold areas, you need a zone that won't freeze. It should be 3 feet deep and 3 feet wide. Don't place a fountain or pump in this deep zone. Dig an 8- to 12-inch shelf for marginal plants (plants that like shallow water). Position the marginal plant shelf so that the plants frame your view of the water garden. Then dig a ledge for the edging as deep as the edging material less 1 inch and slightly less wide. The top of the finished edging should be at least 1 inch above the surrounding terrain to prevent runoff from entering the pond. As you dig, angle the sides slightly, about 20 degrees, and make sure the edges of the pond are level with the other side. If they aren't level, the liner will show. Check by placing a carpenter's level on a long, straight board placed over the hole.
Carefully inspect the hole for sharp stones or roots and remove them. Flexible liners are susceptible to punctures from rocks, gravel, broken tree roots and other sharp objects. Cushion the liner with an underlayment of some kind. Options include 2 to 3 inches of sand, fiberglass insulation material or newspaper. Most water garden suppliers offer a tough, flexible underlayment material specifically designed for use with pond liners. Place your chosen material in the bottom of the hole and on any shelves cut into the sides of the pond. Also, pack damp sand into any holes in the sidewalls where large rocks were removed.
Pick a warm, sunny day to install the liner. Make it more flexible and easier to handle by spreading it out on sun-warmed pavement for 15 to 20 minutes. To avoid punctures, don't drag the liner across the ground. With a helper, drape the liner loosely into the hole with an even overlap on all sides. Then weigh down the edges with a few smooth, flat stones or bricks. Once the liner is in place, begin filling the pond with water. As the pond fills with water, adjust the liner to conform to the sides of the pond, and smooth out as many creases and wrinkles as possible. As the pond fills, ease off the stone weights to avoid overstretching the liner. When the pond is full, trim off excess lining with a utility knife or sharp scissors. Leave enough liner around the pond rim to extend underneath and a few inches behind the first course of edging stones.
To keep the liner in place while adding edging, push 20d nails through the liner into the ground every foot or so around the pond rim. If you're using natural stones, experiment with several arrangements until you find one that looks natural. Although large, flat stones or masonry units can be placed directly over the liner, position them carefully so they won't slip into the pond. To prevent stones from moving, mortar them in place. Mortar comes premixed and is inexpensive.
The ground under these ponds must be firm, stable and free of rocks, projecting roots, and other sharp objects. Keep in mind that a shell full of water can weigh up to 100 pounds or more. Any bumps or empty spaces underneath may cause the shell to crack or buckle. In loose or sandy soil, ground water can cause erosion around the shell, creating empty spaces that weaken it. Similarly, extensive seasonal freezing and thawing of soils can deform or buckle the shell. Backfilling around the shell properly helps to prevent these problems.
Place the preformed shell upright in the desired location. If the shell is completely symmetrical, it can simply be turned upside down and its outline marked directly on the ground. For irregular shapes, use plumbed stakes or a plumb bob to transfer the shape of the pond rim to the ground. Mark the outline with flour, paint or a garden hose. Use stakes, spaced about 12 inches apart, to keep the hose or rope in place.
Dig the hole to conform to the shape of the pond shell, allowing an extra 2 inches around the pond perimeter and 2 to 3 inches in the bottom of the hole. If the shell has shallow-water shelves, cut ledges at the appropriate locations to support them. Shells must be fully supported at all points. Remove any rocks or other sharp objects, then line the bottom of the hole with 2 to 3 inches of damp sand. Flatten the bottom of the hole with a short board, and firmly pack the soil to provide a secure base for the shell. To ensure the bottom of the hole is perfectly level in all directions, place a level on a 2-by-4 laid on the sand base.
With a helper, set the pond shell into the hole and check the height of the rim. It should be about 1 inch above the surrounding ground to prevent runoff from entering the pond. Add or remove soil from the bottom of the hole to achieve the desired height. Place a long, straight 2-by-4 across the shell rim in several places, and check with a level. If the shell isn't level, pull it out of the hole and re-level as necessary.
Make sure the pond is perfectly level before you fill it with water. As the water level rises, backfill the hole around the shell with sifted dirt or damp sand, packing it gently with a shovel handle or the end of a 2-by-4. Make sure you fill all empty spaces, especially around shallow water shelves. Make sure it's level as you go. Don't allow the water inside the pond to rise above the backfilled earth outside the rim or else the shell will tend to bulge outward. Try to equalize the pressure exerted on opposing sides of the shell as you backfill around it.
When the shell is filled with water, you can conceal the exposed rim with rocks, masonry materials or overhanging plants. If you're using flagstones or pavers, allow them to overhang the pond edges by 1 to 2 inches. The weight of the edging may deform or damage the pond walls, so don't allow the full weight of these materials to rest on the pond rim.
Before beginning any excavation, call 811 to check for underground utilities.