A pond in your garden provides an endless source of fascination as you watch pond life take hold and insects, snails, fish and plants establish themselves. Here’s how to build an informal pond that’s suitable for all sizes of gardens.
Choosing your spot
- To position your pond, choose a sunny position away from overhanging trees. You need a minimum area of 3.75 square metres (40 square feet). Any smaller and overheating causes algae problems. Make sure there are no underground services nearby.
- Mark the outline of your pond on the ground with a flexible hose or rope. Try a traditional kidney shape for a distinctive look.
- Irregularly shaped or informal ponds look better further from the house and most natural in the lowest part of the garden.
Preparing the base
- Dig down 250mm (10in) to form a ledge 250mm (10in) wide.
- Dig down another 300mm (1foot) minimum. If the total area is over 9 cubic metres (100 cubic feet) the depth should be at least 60cm (2ft) in the centre.
- Don’t just get rid of the soil you excavate – you can use it to make another garden feature, like a raised bed or rock garden.
Check the pond is level
Check all sides are level by using a long pole and spirit level.
Check that the sides slope in at about a 20° angle.
Remove any sharp stones and twigs.
Ensure that when a surrounding of stones has been added, they will rest about 25mm (1in) below the level of surrounding turf.
- If possible, provide a shallow sloping edge in one section to allow wildlife to climb in and out – a pebbly shelf extending out into a flower bed is effective.
- Make one piece of the edge 50mm (2in) lower and add a drain leading to a soak-a-way to avoid overflowing.
Lining and filling the pond
- Add a 18mm (3/4in) layer of damp sand over the bottom and sides to cushion the liner.
- Calculate the area of butyl liner required with the following formula: (maximum length + twice depth) x (maximum width + twice depth).
- Stretch the liner over the hole and anchor the edges with bricks. Allow to warm and stretch in the sun for a few hours.
- Fill with water until the bottom of the drain is reached – this should be an even 50mm (2in) from the top all the way round. Slowly remove the bricks as the pond fills up to ensure the liner snugly fits the shape.
- Cut the edge of the liner about 225mm (9in) outside the rim. Trim and fold any surplus and peg into the ground with wire.
- Add paving or decorative stones to hide the liner, overhanging the edge by 50mm (2in). This will shield the liner from sunlight and hide it from view.
- Finally, seal with blobs of mortar (a ratio of 3:1 sand to cement) around the outside. Do not allow any mortar to fall into the water – this is poisonous to fish and will mean you will have to replace the water before you add any wildlife.
- You can add a range of water plants after a few days, but wait a month for the pond to settle before adding any fish.