Why a small pond earns its keep

Even a pond the size of a dining table will pull wildlife into your garden within a single season. On a warm May evening, that puddle becomes a hunting ground for bats, a nursery for frogs and newts, and a landing strip for dragonflies that may have travelled a kilometre from the nearest stream. Unlike a feeder or a nest box, water offers drinking, bathing, breeding and shelter all in one place, which is why it is the most effective single thing most of us can add to a modest British garden. The good news is that you do not need a butyl sheet, a pump or an electrician. With a little patience and a few bags of bentonite clay — or a rigid preformed basin for a smaller, quicker build — you can make a pond that looks as though it has always been there.

Bentonite clay or a preformed basin — picking your route

Sodium bentonite is a natural clay that swells dramatically when wet, forming a self-sealing membrane. It suits an informal, softly edged pond and it is astonishingly cheap compared with a rubber liner. The technique is straightforward but it must be done in dry weather.

• Spread the clay in two or three thin layers, roughly 5 to 8 kg per square metre in total, aiming for a finished thickness of 10 to 15 cm.
• Tamp each layer firmly with the back of a spade or a roller, then mist it lightly so it binds to the layer below.
• Carry the clay up and just over the rim of the pond, tucking it under turf or stones to lock the edge.
• Cap it with 5 to 10 cm of subsoil or sharp sand to protect the membrane from roots, claws and ultraviolet light.

The main risks are punctures from nearby tree roots and cracking if the clay dries out completely. Keep the pond topped up through dry spells, and site it well away from willow, poplar and conifer roots. If your garden is tiny, a preformed basin is the pragmatic option: choose one made from recycled composite or glass-reinforced plastic rather than a thin sheet liner, and look for a model with a shallow shelf moulded in. If you buy second-hand, check it for hairline cracks before you dig.

Digging in a gentle slope for safe access

This is the detail that separates a wildlife pond from a decorative one. Every creature that enters must be able to climb out again, and hedgehogs, frogs, fledglings and exhausted bees all drown in steep-sided water. Shape one end of the pond as a shallow beach, sloping at roughly one in four from the rim down to the water, and finish it with gravel or flat stones so there is grip underfoot.

Aim for a depth of 40 to 60 cm in the middle, which is deep enough to stay cool and unfrozen at the bottom in winter, and include a shelf about 20 cm below the waterline for marginal plants. If you are using a rigid basin with vertical walls, build an escape ramp from stones or a piece of weathered timber angled from the base to the rim. Let turf or gravel trail into the water on at least one side, and leave a few longer stems and stones around the edge so amphibians have cover on their approach.

Planting: native oxygenators and a few marginals

You need oxygenators to keep the water clear, but a small pond is easily overwhelmed — cover no more than a third of the surface. Plant them in baskets of garden soil topped with gravel, never in compost, which leaks nutrients and triggers algae.

• Hornwort and water starwort are unfussy native oxygenators that float free and need no planting at all.
• Spiked water-milfoil and native water crowfoot root well in a basket on the deeper shelf.
• For the margins, try marsh marigold, water forget-me-not, brooklime and water mint — all nectar-rich and compact enough for a small pond.

Steer clear of invasive thugs such as parrot's feather and New Zealand pygmyweed, which is illegal to plant in the wild and almost impossible to remove once established. Skip the fish, too. Goldfish eat tadpoles and churn up the silt, and a wildlife pond simply does not need them.

Filling, settling and the first season

Fill from a water butt wherever possible. Tap water carries chlorine, fluoride and, more importantly, phosphates and nitrates that feed blanket weed and green algae. If you must use the hose, let the water stand in a butt for a few days first, and accept that the first summer will look a bit soupy while the plants establish and the microscopic life finds its balance. Resist the urge to empty and start again. By the following spring, the water should clear on its own as submerged plants and grazing invertebrates take hold. Top up with rainwater, and never add fertiliser, weedkiller or fish food anywhere near it.

A cosy corner to sit and watch

Put a bench or two folding chairs on the north side of the pond, facing south, so you look across the water without the sun in your eyes. A gravel or decked sitting area, a couple of log rounds for a mug of tea, and a lantern on a hook will turn the pond edge into the most restful square metre of the garden. Keep night lighting low and aimed away from the water; a submerged or upland glow disturbs amphibians and bats, whilst a candle or a warm, shielded lamp gives you just enough to watch the ripples. Plant tall grasses and a shrub behind the seat to break the wind, and leave a small pile of stones and deadwood nearby. Then simply sit still for twenty minutes at dusk — something will always arrive.