How to build a garden pond (with filter, plants & materials list)

Step by step

1. 1Mark out the pond shape with a hose or rope and check the edges are level with a spirit level.
2. 2Dig the planting shelf (20–30 cm) around the edge, then the deep zone (at least 60–80 cm).
3. 3Remove sharp stones and roots, then lay protective fleece (or a sand bed) over the whole hole.
4. 4Drape the flexible liner into the hole and smooth out the big folds; weigh the edges down.
5. 5Fill slowly with water so the liner settles into shape, then trim the excess, leaving a 30 cm overlap.
6. 6Install the pump and filter (skip this for a wildlife pond) and run the hose back to the pond.
7. 7Add planting baskets on the shelves and edge the pond with stone to hide and hold the liner.
8. 8Treat tap water with a dechlorinator and let the pond settle 2–4 weeks before adding any fish.

Plan it first

• ✓Pick a spot with morning sun but partial afternoon shade (4–6 hours of light) — full sun fuels algae, deep shade weakens plants.
• ✓Keep it away from large trees so falling leaves and roots don’t foul the water.
• ✓Plan depth zones: a 20–30 cm planting shelf around the edge and a deep zone of at least 60–80 cm (80–100 cm in cold-winter regions) so fish and wildlife can overwinter.
• ✓Check for buried cables and pipes before you dig, and think about child safety (a shallow pebble beach or a mesh are safer near small kids).
• ✓Sketch the pond on your plan in LushAI first — drag in the shape, surrounding stone, planting and a deck, and render it photorealistically so you can see the result before you lift a spade.

Materials & tools to buy

• ✓Flexible pond liner (EPDM lasts longest; PVC is cheaper). Size it: length + 2× depth + 30 cm overlap, same for the width.
• ✓Protective underlay fleece (or a 3–5 cm sand bed) to stop stones puncturing the liner.
• ✓Pond pump — pick one that circulates the whole pond volume roughly once per hour.
• ✓Filter (mechanical foam + biological media); add a UV clarifier if you want to prevent green water.
• ✓Flexible hose to match the pump/filter outlets, plus an outdoor RCD-protected power supply.
• ✓Edging stones or rock, planting baskets, aquatic soil and washed gravel to top the baskets.
• ✓Water conditioner (dechlorinator) for tap water, plus aquatic plants (oxygenators, marginals, one water lily).
• ✓Tools: spade, marking paint or a hose/rope, spirit level on a straight board, wheelbarrow, and a sharp knife or scissors.

Filtration & pumps

• ✓A pump pushes water through the filter and back to the pond — size both to the pond volume and how many fish you keep.
• ✓Mechanical filtration (foam) traps debris; biological media grows the bacteria that break down fish waste and keep the water clear.
• ✓A UV clarifier clumps the algae that turns water green so the filter can catch it — optional but effective.
• ✓Run the pump continuously in the warm months, and add a small waterfall or fountain to oxygenate the water.
• ✓Clean filter foams in a bucket of pond water, never under the tap — chlorine kills the helpful bacteria.

Ecological & wildlife ponds

• ✓An ecological pond needs no pump, filter or electricity — the right plants do the cleaning and the system finds its own balance.
• ✓Give it a gently sloping pebble “beach” on one side so frogs, hedgehogs and birds can get in and out safely.
• ✓Let native oxygenating and marginal plants cover the surface and feed on nutrients, starving the algae instead of fighting them.
• ✓Skip the fish: a wildlife pond attracts frogs, newts, dragonflies and pollinators on its own, and stays clearer without them.
• ✓Top up with rainwater where you can, and let leaves and stems stand over winter as shelter.

Plants, fish & maintenance

• ✓Plant in three layers: submerged oxygenators, marginals on the shelves, and a floating water lily to shade about a third of the surface.
• ✓Wait 2–4 weeks after planting before adding fish so the filter bacteria establish — then stock gradually and don’t overfeed.
• ✓In autumn, net the pond to keep leaves out; in winter keep a hole open in the ice (a floating de-icer) so gases can escape.
• ✓Top up with rainwater, thin overgrown plants each year, and you’ll have a clear, living pond with very little work.

FAQ

How deep should a garden pond be?

At least 60–80 cm in the deepest part (80–100 cm in cold-winter regions) so fish and wildlife can overwinter, plus 20–30 cm shelves around the edge for marginal plants.

Do I need a pump and filter?

For a pond with fish, yes — they keep the water clear and healthy. A planted wildlife pond needs neither: the plants do the filtering and it balances itself.

How much does it cost to build a pond?

A small DIY wildlife pond costs roughly €150–400 in liner, underlay and plants. A larger pond with a pump, filter and stone edging is typically €600–2,000+ depending on size.

How do I stop the water turning green?

Shade about a third of the surface with floating plants, add submerged oxygenators, avoid overstocking or overfeeding fish, and optionally fit a UV clarifier.

When can I add fish?

Wait 2–4 weeks after planting and filling so the filter bacteria establish, then add fish gradually rather than all at once.