Pond liners
Pond liners keep water from seeping into the soil. Even in heavy clay soils, a liner is necessary. You can buy rigid pond liners in a variety of shapes. These are durable and may include built-in waterfalls. Many are quite small. If you want a larger pool or would like to design your own shape, consider using a polyvinyl chloride (PVC) liner. Use a liner specifically designed for pools. While other plastics initially may be cheaper, many are not resistant to ultraviolet light and will break down quickly. Some plastics may also be toxic to fish. Liners also come in different thickness. A thicker liner tends to be more resistant to punctures. While expensive and requiring more expertise to install, cement is also an option as a pool liner.
If you use PVC, you will need to get a liner large enough for your pool. To determine how large apiece you will need, determine the maximum width, length, and depth of your pond. Multiply the maximum depth by 3. Then add this number to both the length and width. This will allow enough plastic to be securely held down around all pond edges.
Installing the pond
You can put in a backyard pond anytime the ground is not frozen or overly wet. If using a pre-formed liner, dig a hole to the correct depth and slightly wider. Insert the liner, making sure it is level and sits securely in the ground. Backfill around the sides, add water, pump, and plants. Complete landscaping around the pool.
If you use a PVC liner, plan on at least a weekend to install and landscape.
Steps to install a pond with a PVC liner:
Decide on your pond's location. Using a hose or rope, lay out the shape of your pond on the ground. Once you are happy with the shape, start digging. Stockpile your topsoil so you can use it to landscape around your pond.
Plan for part of your pond being at least 18 to 24 inches deep; 24 to 36 inches is even better. This will allow for a greater diversity of plants and fish to live in the pond. You may want to make tiers around the inside of the pond at various depths on which to place pots of different aquatic plants. Make tiers about 12 inches wide to accommodate the pots.
Remove any rocks from the excavated area. To help prevent punctures in the plastic, put a one-inch layer of damp sand on the bottom of the excavated area. Spread the plastic liner over the hole. Let it sag gently in the hole. Place a few rocks or bricks around the edge to hold in place.
Slowly start filling your pond. The weight of the water will help smooth out the liner. Remove rocks holding the edges to allow liner to conform to the edges of the hole. Smooth out wrinkles but do not pull too tightly. You can walk on the liner if you remove your shoes.
Finish off the pond by placing rocks around the edge to securely hold the liner in place. Install the pump and filter, if desired. Many smaller pumps have a built-in filter. For larger pools, a separate pump and filter may be necessary. Make sure the filter and pump is adequate for the volume of water in your pond. Pumps not only add interest, but also are important in adding oxygen to the water. If you want a fountain or waterfall in your pond, you will need a pump to circulate the water.
Let the pond sit for a few days before adding fish and plants. This allows chlorine to evaporate from the water. Chemicals are also available that will quickly neutralize chlorine and other harmful compounds. Place plants at various depths and add fish.