A pond is the single most valuable thing you can add to a garden for wildlife. It need not be large, and it need not be expensive. Even a hollow the size of a washing-up bowl will be claimed by pond skaters within a fortnight, and a modest pool of a metre and a half can support frogs, newts and half a dozen species of dragonfly. What matters is siting it thoughtfully, lining it without chemicals and planting it with native species.

Choose the Right Spot Before You Dig

Position is everything, and it is far easier to get right before you pick up a spade. Aim for a spot that receives sun for at least half the day. Warmth speeds up tadpole development and encourages water lilies to flower, while a little afternoon shade helps keep algae in check. Full sun all day, especially in a shallow pool, will simply turn the water green.

Avoid the following:

• Beneath trees and large shrubs. Roots can puncture a liner, and fallen leaves rot down, stripping oxygen from the water and feeding blanketweed.
• Low-lying corners where runoff collects. Water draining from a road, a fertilised lawn or a patio can carry pollutants straight into your pond.
• Anywhere you routinely use weedkiller or slug pellets. Amphibians are extremely sensitive to garden chemicals, and residues wash in with the rain.
• Somewhere you cannot see. A pond in view of the kitchen window gets watched, enjoyed and looked after.

Pick level ground so the liner sits evenly, and site the pond within reach of a water butt or downpipe for topping up in summer.

Size, Shape and Depth

Bigger is genuinely more stable, but a pond of two metres by three is ample for a rich community of wildlife. Depth matters more than width. Aim for 60 to 75 centimetres at the deepest point, and nearer 90 centimetres if you garden in an exposed or frosty spot. Deep water stays cooler in summer and is far less likely to freeze solid in winter, which gives frogs and newts somewhere safe to sit out a cold snap.

Build in variation. A shallow shelf of 20 to 30 centimetres will hold marginal plants, and a gently sloping beach of just a few centimetres at one edge gives birds somewhere to bathe, hedgehogs a safe drink and froglets an easy exit. Irregular, wavy edges create more habitat than a neat circle. If your soil is heavy clay, you may find it holds water with no liner at all — puddle it well and watch the level for a fortnight before deciding.

Lining It Without Chemicals

Butyl rubber, sometimes sold as EPDM, is the best choice for a wildlife pond. It is flexible, harmless to aquatic life and lasts twenty-five years or more. Cheaper PVC goes brittle and cracks within a decade. Rigid preformed liners work well in small gardens, though they limit your design; concrete should be avoided or carefully sealed, as fresh lime raises the pH and can harm wildlife.

Whatever you choose, lay a protective underlay first — old carpet, a layer of sand or purpose-made fleece. Order the liner generously: pond length plus twice the maximum depth, plus a 60-centimetre overlap on every side for the edging. Once laid, fill with rainwater from a butt if you can. Tap water is perfectly acceptable — the chlorine disperses naturally within a few days — but let the pond stand for a fortnight before introducing plants so the temperature settles.

Never use algaecides, dyes, or any liner treatment. A wildlife pond is a living system, and chemicals that kill algae will also kill the invertebrates that feed the frogs.

Planting It Up With Natives

Native plants support far more insect life than exotic varieties. Plant in late spring, once the water has warmed, using baskets lined with hessian and filled with low-nutrient aquatic compost or garden loam. Ordinary multipurpose compost is far too rich; nutrients leach out and trigger the very algae you are trying to avoid.

• Oxygenators: hornwort and water starwort, which live entirely underwater.
• Floating plants: the native white water lily, or a smaller variety for a modest pond.
• Marginals: marsh marigold, water forget-me-not, yellow flag iris, purple loosestrife, ragged robin, lesser spearwort and soft rush.

Steer clear of invasive non-natives such as floating pennywort, parrot's feather and New Zealand pygmyweed — they smother a pond within a season. Aim for floating leaves to cover a third to a half of the surface by the third year; the shade keeps the water clear and gives froglets somewhere to hide.

Encouraging Residents

If the habitat is right, wildlife will arrive on its own. Frogs, toads, newts, diving beetles, damselflies and dragonflies all colonise quickly, and birds will drop in to drink and bathe. Do not add fish: even a few goldfish will clear out tadpoles, newt larvae and dragonfly nymphs.

Do not move frogspawn in from elsewhere either, as it risks spreading disease and invasive weeds. Instead, make your pond easy to reach and leave a rough corner nearby — a log pile, some long grass and a patch of nettles will shelter amphibians through the winter. Add a piece of rough timber or a stack of stones as a ramp so nothing gets trapped, and resist the temptation to light the pond at night; bats hunt over dark water.

Looking After It Through the Year

Maintenance is light, and mostly about doing less. In spring, twirl surplus blanketweed around a cane and lift it out; barley straw can help if the problem persists. Top up in summer with rainwater. In autumn, skim a few leaves but leave the margins standing — seedheads and hollow stems shelter overwintering insects. In winter, never smash the ice, as the shock waves injure frogs and newts; rest a pan of hot water on the surface to melt a hole instead. Frogs often overwinter in the mud at the bottom, so leave decaying plant matter undisturbed until spring.

Get those basics right and your pond will reward you within a single season — a small patch of still water that hums with life from the first warm evening of the year.