Create a wildlife-friendly garden pond without using plastic

Why a plastic-free pond is worth the effort

A pond is the single most effective thing you can add to a garden for wildlife. Even a modest one — a metre or two across — will draw in frogs, toads, hedgehogs, bats, dragonflies and a steady parade of birds looking for a drink and a bath. Most pond kits, though, are built around a butyl or PVC liner. Those are durable, but they are also manufactured, shipped and eventually dug out and sent to landfill. If you would rather your pond sat lightly on the land, you can build one that seals itself using nothing more exotic than clay, soil and patience.

This is not a fringe idea. Long before flexible liners existed, every dew pond, farm pond and village duck pond in Britain was sealed with puddled clay, and plenty of them still hold water today. A natural pond also behaves better: it supports a richer community of microscopic life, plants root into the substrate instead of sitting in baskets, and there is no rubber edge peeking out from under the turf.

Choosing the spot and digging the shape

Pick a position that gets sun for at least half the day — dragonflies and most aquatic plants need warmth — but avoid sitting it directly under a mature deciduous tree, or you will spend every autumn fishing out leaves. Keep it away from the base of buildings and away from where you spread fertiliser or weedkiller.

• Aim for a centre depth of around 60cm, with broad shelves at 20–25cm for marginal plants.
• Include at least one gently sloping beach so frogs, hedgehogs and small birds can walk in and out safely.
• Make the outline irregular. Wavy edges, a shallow spit of gravel and a couple of hidden corners create far more habitat than a circle.
• Keep the rim level. Check it with a straight board and a spirit level before you go any further.

As you dig, keep the topsoil in one pile and the subsoil in another. You will want the topsoil back on the shelves and around the margins.

Sealing the pond without a liner

There are three dependable approaches, and which one suits you depends entirely on your soil.

Puddling clay. If you have clay on site, you are in luck. Remove stones and roots from the subsoil, add water and tread it thoroughly — traditionally with bare feet or boots — until it becomes a stiff, smooth, sausage-like consistency. Lay it in 10–15cm layers, working each one into the last, and aim for a finished thickness of 20–30cm. Keep it permanently wet while you work and cover it with a layer of topsoil once finished.

Bentonite. On sandier ground, powdered sodium bentonite clay can be rotavated into the top 10–15cm of damp subsoil at roughly 5–10kg per square metre, then covered with 10cm of soil. It swells on contact with water and forms a reliable seal. It is unforgiving of roots and stones, so clear the base meticulously.

Gleying. This is the slow, cheap, beautiful option. Dig the hole, break up the base, remove stones, then saturate the soil and tread it into a puddled slime. Spread a thin layer of well-rotted manure or compost, then straw, then tread again. Repeat the layers and keep the pond topped up with rainwater. Over a season or two, anaerobic bacteria seal the base naturally. It can be slow to hold water at first, so be patient.

Planting for frogs, dragonflies and birds

Use native species and plant generously, but avoid the thugs. Never introduce floating pennywort, parrot's feather or water fern — they are invasive and illegal to plant in the wild. Good choices include marsh marigold, water forget-me-not, flowering rush and yellow flag iris around the margins, with hornwort and water starwort submerged as oxygenators.

Dragonfly larvae need vertical stems to climb when they emerge as adults, so leave some emergent plants standing over winter. Frogs need cover to hide in, and birds need a shallow, pebbly edge where they can bathe without getting out of their depth. A few flat stones placed just below the waterline do all three jobs at once.

Shelter, edges and the small details

• Leave a strip of long grass and nettles along one side — amphibians use it as a corridor.
• Stack a small pile of logs and stones nearby as a hibernation spot.
• Resist the urge to tidy the margins. Seed heads feed birds and insects.
• Add a stone or half-submerged branch as a ramp for anything that falls in.
• Skip the fish. They eat tadpoles and dragonfly larvae, and they cloud the water.

Caring for the pond through the year

Top up with rainwater from a butt, never tap water — the nutrients and chlorine encourage algae. In autumn, scoop out fallen leaves, but leave the debris that settles at the bottom, as it is food and shelter for overwintering larvae. In late summer, thin oxygenators by hand rather than draining the pond. Once every few years, clear a third of the plants at most, and always in early autumn when the breeding season is over.

If you are lucky enough to find great crested newts, do stop and seek advice before carrying out any work — they are protected by law. Otherwise, the golden rule is simple: do less. A natural pond left largely to its own devices will settle into a balance that no filter or pump can match.