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Extension > Garden > SULIS > Implementation > Building a Flexible Lined Pond

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Building a Flexible Lined Pond


Using a flexible pond liner, it is possible to create a pond of virtually any size or shape. This flexibility allows for a natural looking, unique pond. The pond described here is small and does not include a circulating pump or drain.

A Pond

Amount, Specifications & Supplies:

Pond liner of appropriate size to cover bottom and sides of the desired pond. Liners are made from several different materials, the most common being PVC and butyl rubber. Strengths range from 20 ml to 60 ml. Follow manufacturer's suggestions regarding the best strength for your pond size and depth.

Underlayment made of polypropylene or polyester. This is placed under the linear and protects it from loose rocks, roots or other sharp objects.

Sand, enough to provide a 4-5" depth over the entire pond.

Flat stones, field stones, or other desired material to edge the pond and hide the edges of the pond liner.

Tools and Equipment:

  • Rope or garden hose to lay out the freeform pond shape
  • Stakes, flags or spray paint to mark pond boundaries
  • Tape measure
  • Spade to excavate pond area, backhoe for large areas
  • Carpenter's level
  • 2" x 4" board long enough to span the pond width for leveling
  • Rubber hammer
  • Wheelbarrow or skid loader to haul sand, stones, field stones, etc.

Site Considerations:

The area chosen for the pond should have sufficient sunlight to support the plants desired. Ponds under the canopies of trees look good but require more cleaning. Ice and snow shorten pond liner life. Heavier ml pond liners materials are recommended. Wooded areas with large roots should also be avoided. Always be sure to locate underground utility lines before excavating.

Step-By-Step Process:

1. Outline the shape of the pond using a rope or garden hose. Using stakes or flags, mark the final pond shape. A permanent way to mark the pond shape is to spray paint onto the ground, following the shape formed by the hose or rope.

2. Excavate the area using a shovel or skid loader. Create a shelf around the edge to place the first layer of flat stones or field stones. The shelf should be 8" deep and 12" wide. The sides of the pond should have a very gentle slope of 4 to 1 or 5 to 1. A gentle slope will allow animals or small children to climb out should they accidentally fall in.

Diagram of Step by Step Process

3. Be sure the edge and shelf of the pond is level all around. If one side of the pond is higher than the other, the water will not cover the liner on the higher side. Use the 2" x 4" board and carpenter's level to span the pond. Move the 2" x 4" board around the pond making sure the pond edge is level in all directions. Remove any stones, roots or debris that could cause the pond to look uneven or that might cause damage to the liner.

4. Determine the size of the liner needed by measuring the depth, length and width of the hole in feet. Measure the depth of the pond at its deepest point first. Next, measure the width of the pond at its widest point and to that number, add twice the depth. Then add two feet for edging.

Determine the length of the liner needed in the same manner: measure the length at the longest point of the pond and add two times the depth, plus two feet for edging. Liner width = pond width + 2 x pond depth + 2 feet.

5. Place a 4"-5" layer of damp coarse sand on the bottom of the pond. This will create a smooth base for the liner to lay on, and will help prevent punctures. If the sand will not stay on the sides, the slope is too steep. Underlayment can be placed along the bottom and sides of the pond to protect the liner from damage. Determine the amount of underlayment needed in the same way as the liner.

Pond Bed

Liner length = pond length + 2 x pond depth + 2 feet

6. Carefully place the folded liner in the center of the pond and begin to unfold it. Allow the sun to warm it for a few minutes so that it becomes more flexible. Carefully position the unfolded liner so that an equal amount for edging is available around the entire pond. Be sure to avoid damaging the shelves or sand base when laying out the liner. Recheck levels after the liner is in place.

Pond Liner

7. Fill the pond with water while monitoring the liner to be sure no part slips down and no air pockets form under the liner. Carefully distribute small creases on the sides of the pond as the water level rises. Fill the pond to within 1" of the top edge.

Pond Being Filled with Water

8. Trim the excess liner to a maximum of 18". Place field stones or flat stones on the shelf around the pond. This first layer of rocks will be partially submerged in water.

9. Wrap the excess liner around the first or second layer of stones on the shelf. Place the next row of stones on top of the liner to hide its appearance. Fold or trim the liner if necessary to be sure it will not be visible. If using flat stones, level each one as it is placed around the pond.

Diagram of a Pond

Arrange additional stones in an attractive manner around the edge of the pond and throughout the landscape that surrounds it.

Additional Stones Around the Pond Stones by Ponds Surroundings

10. Plant around the pond to soften the edges and to blend the pond into the landscape. Plants should cover some of the rocks but not all.

Plant Cover

11. Ponds without drains or aerators will need to be emptied and cleaned every spring and at least once during the season. A sump pump is a good way to empty the pond.

Emptied Pond

This implementation report is based on landscape projects completed by University of Minnesota students enrolled in landscape design and implementation courses, Department of Horticultural Science.

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