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Water garden feature

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Water gardening has become the fastest-growing trend in landscaping, with prospects of tranquility and property enhancement inspiring floods of interest in the topic. If you’ve thought about jumping in but feared you might end up in a sea of maintenance problems, check out our pond. The water’s fine! Best of all, it’s virtually self-sustaining.

Building a water feature that successfully mimics nature’s ecosystem can free you from chores such as monitoring water quality, balancing chemicals, repairing leaks and nursing sick plants and fish. We learned about this approach to pond construction and care from Club member Ray “Dr. Pond” Campbell of Lost Eden Ponds in Clearwater, Minnesota. He showed us how to build a balanced water garden that includes a filtering bog, a cascading stream and a fishpond.

How It Works

The process is simple, but it does involve heavy labor. In a nutshell, you dig holes for the pond and bog, carve a streambed, line it all with fabric and a waterproof liner, add culverts, a pump, rocks and water, and finish with plants and fish.

In his classes for would-be pond owners, Ray explains that a healthy water feature requires a combination of components. This bog/pond design achieves a balance because it includes a cascading stream and a bog garden as well as vegetation and fish. As water flows through the system, it is aerated and filtered — just as a natural stream would be.

Size, Shape and Siting

It’s easy to plan the size, shape and location of a water feature to fit your yard’s available space and landscaping. Our 6 x 8-ft. pond is relatively small because it was made to fit within an existing fenced area. But with more space and materials (and energy), you can build a water feature as large as you want. In fact, larger is better because a higher volume of water keeps the system more easily balanced.

This bog/stream/pond works well on either a flat area or a hill. We placed ours on a slope that has a total drop of less than 2 ft. Whatever the grade, create a series of steps down rather than one or two large falls to minimise water loss.

To achieve a natural look, we chose an irregular shape for the outline of our water feature. If you want a formal water garden, you could choose a more symmetrical or a geometric shape and use materials such as brick or uniform stones.

Before you decide on a site, check local codes regarding setback distances, fence requirements and electrical permits, and have all utilities’ locations marked so you don’t hit any pipes or cables during excavation. You must also factor nature into your site decision. Naturally moist or poorly drained soil is not a good location for an artificial body of water because of erratic freeze-thaw cycles, unstable soil and potential flooding. And to avoid runoff of lawn chemicals and other pollutants, do not choose a low area of your yard. Consider these additional guidelines as well:

  • Locate your pond near a water supply and an exterior-rated electrical outlet (equipped with a GFCI). Consult an electrician if you need to add an outlet.
  • Because most water-garden plants like plenty of sunlight, avoid heavily shaded areas. Overhanging branches also drop leaves, twigs, blossoms and seeds into the water.
  • To fully enjoy your water feature, choose a location that you can easily view from your outdoor living area. We created ours close to the house and deck.

Excavation

Once you’ve chosen a location and determined the outline of your pond, stream and bog area, mark the ground; then excavate the pond, bog and streambed. You’ll use some of the soil to landscape around the water feature, but you’ll probably need a spot (nearby if possible) to deposit the leftovers. To prevent settling, tamp any soil that is added to or disturbed within your water garden area.

Ray recommends using a surveyor’s level to be sure that the excavation is level and that the edges hold water.

The pond’s perimeter should vary in height for a natural look, but you need to create one low edge so that overflow due to heavy rains and snowmelt will be directed away from nearby structures. Use the low spot as a benchmark for establishing pond depth. Dig within the outlined shape of the pond, grading the entire inside area to be level with a point that is 8 in. below the benchmark. (Most edges of the pond will be more than 8 in. high.) About 10 to 16 in. from the edge, outline and dig a second level at least 8 in. deeper. Create the resulting tier to vary in width and have a slight grade toward the centre of the pond so debris will flow toward the pump. The shelf provides a home for plants and a spot for people to safely step in or out of the pond if necessary.

You can carve a third level in the centre if your pond is larger; just be sure you reach a total depth of at least 24 in. — the minimum depth for fish to survive winter in a northern climate. Finally, dig a 10-in.-deep x 16-in.-wide trench across the pond floor to hold the culvert tube. Grade the trench slightly downward toward the pump end.

Next, dig the bog area, which in our project is a 4-ft.-dia. x 3-ft.-deep pit with straight sides. Mound and tamp some of the excavated soil around the edges of the bog to create a berm for blocking runoff of lawn chemicals and grass clippings. In the floor of the bog, create a trench for the second culvert. Check that the culvert assemblies fit in the trenches of both the pond and the bog, and adjust the soil as necessary. At the top of the stream, dig a deeper recess to act as a holding pond (photo, left). Form the stream with stepped tiers, each with a gentle backward slope so that all of the water doesn’t drain to the pond if the pump is turned off. The stream tiers must be level side-to-side. At the front edge of each step, form the grade level to be at least 6 in. higher than the stream.

Finally, dig a narrow 12-in.-deep trench (sloping slightly towards the pump) next to the water feature. This where you will bury the flexible PVC tubing that carries the water from the pump to the bog.

Adding Components

Once you’ve prepared the site, install the components that contain, circulate and filter the water. Consider the following guidelines:

• Underlayment and liner — Before placing the underlayment, clear away all sticks, roots, stones, etc. As you install the waterproof liner, be sure to press the liner tightly into curves and corners so the weight of rocks and water will not stretch it across any voids. Arrange the liner so at least 12 in. wraps over the edges of the entire water feature.

• Culvert — First cut a section to fit the full length of the pond and a second piece that matches the depth of the pond when the sections are attached to the elbow. Bore 2-in. holes and assemble as shown (photos, p. 34). Make another assembly to fit the length and depth of the bog.

Set the assembled culvert sections in place, making sure the tops of the vertical sections are about 2 in. below grade at both ends of the system. Trim the underlayment and EPDM liner to 12 in. along the edges of the water feature. You can trim them to 6 in. after the water feature is lined with rock and filled with water.

• Pump and tubing — Attach the connector and the flexible PVC tubing to the pump (see photos). After lowering the pump into the culvert, cut the PVC and install a 2-in. hose clamp to create a joint that enables you to disconnect the line if you need to replace or remove the pump.

Cut the PVC tube again, at grade level, and rejoin it with a 2-in. ball shutoff valve. Lay the tubing in the narrow trench next to the water feature so it extends from the pump to the floor of the bog. Install a second ball valve just above grade at the bog end as well. Then insert the tube into the horizontal end of the bog culvert.

• Rock — Starting with the largest rocks, fill around the culvert assembly in the pond (photos, above). Add smaller rocks as you go, filling spaces between the larger ones. Periodically check that the liner fits against the soil as tightly as possible and that it reaches well over the edges of the excavated area. Adjust folds to distribute them evenly and minimise bulk.

Work your way upstream, setting large rocks along the sides and in front of the stepped edges. Line the bog with rock as described for the pond, starting with the largest rocks and fitting smaller ones between. Fill to about two-thirds full; then add gravel (1-1/2- to 2-in.-dia. river rock) to fill nearly to the top of the bog. Layer at least 3 in. of additional gravel on the floors of the pond and stream to create a bed for plants and to hide the liner.

Cover the top of each culvert assembly with flagstone and a few decorative rocks. Place more rocks of varying sizes and colours around the entire water feature, in random positions for a natural look. Backfill the trench that holds the 2-in. flexible PVC tube.

Finishing

With the components in place, it’s time to add water, plants and fish. Unless your water comes from a private well, it likely contains chlorine, which is unsafe for fish. Once you’ve filled the pond and bog, begin to operate the pump, but wait a few days for the chlorine to dissipate, or add pond dechlorinator (available at garden supply stores). The circulation will also clear the mud from the water. Your new ecosystem should be self-sustaining in a few seasons as the algae, plants, fish and bacteria levels establish a balance.

Before choosing water-garden plants, talk with experts to learn which plants are hardy in your area. You’ll want to eventually cover at least one-third of the pond surface with a variety of plants, including water lilies, marginals (shallow-water plants, such as iris and grasses) and oxygenators (such as water hyacinth). We planted grasses in the bog area as well, which will eventually spread to cover the gravel bed of the bog.

Planting is easy. Just remove the plant from the pot, wash all of the soil from the roots and bury the roots directly in the gravel. Start with hardy perennials and gradually add tropical plants if you desire.

Once the water and plants are in place, complete the ecosystem with fish. Ray recommends starting with young koi (or goldfish) so they learn about the dangers of predators in a natural setting. When adding to an existing fish population, quarantine newcomers in a separate tank for a couple of weeks to ensure they are healthy. Follow the supplier’s advice on how to acclimate fish to a new body of water. Although fish require initial care, don’t be intimidated; you may soon find that they are your favourite part of being master of your own ecosystem.

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