A pond is one of the fastest ways to bring a barn conversion's grounds to life. Fill it in spring and by midsummer you can reasonably expect common frogs, a patrol of damselflies and a steady traffic of birds using it as a drinking and bathing station. Get the siting and planting right and it will largely look after itself for years.

Why a Pond Suits a Rural Plot

Most barn conversions come with land that has been worked hard: compacted yards, gravel hardstanding, grass mown to within an inch of its life. That is a blank canvas. A pond adds the one thing the surrounding farmland usually lacks — still, open fresh water. Ponds have declined sharply across lowland Britain over the past century, so anything you create is genuinely useful rather than merely decorative.

Farm conversions also have practical advantages. Spoil from service trenches, spare stone from a demolished lean-to and leftover pipework can all be reused in the build. A pond tucked beside an old brick wall, with a stone ledge for basking, looks as though it has always been there.

Choosing the Right Spot

Sunlight is the first consideration. Aim for at least six hours of direct sun a day. Shaded ponds stay cold, and cold water slows the insect life that feeds everything further up the chain.

• Distance from the building: keep open water at least five metres from the barn's footings and any retained walls. Constant ground moisture can soften foundations, and you want to walk the margin without squeezing past a wall.
• Run-off: never site a pond downhill of a concrete yard, silage clamp, muck heap or oil store. Nutrients will turn it green; hydrocarbons will sour it.
• Underground services: check where the foul drainage, soakaway and water main run before you dig. A pond over a soakaway will not hold water, and one over field drains may empty every time the land is wet.
• Trees: stay outside the root spread of willows and poplars, and at least eight metres from deciduous trees. Leaves sink, rot and feed blanketweed.

Shape, Depth and Water Source

Two metres by three is workable; anything larger holds a more stable temperature and supports more species. Dig a central area 60–90cm deep, then create shelves at roughly 20cm and 40cm for different plants, and finish with gently sloping beaches on at least two sides. Steep-sided ponds are a death trap for hedgehogs and froglets.

For lining, butyl gives the longest life, though puddled clay suits heavy soils and looks more natural. Fill from rainwater butts fed off a clean roof — slate, tile or metal are ideal. Avoid roof run-off if the covering has recently been treated with bitumen, paint or a moss killer, and fit a first-flush diverter so the initial grimy wash goes elsewhere. If you must use tap water, let it stand for a few days before adding plants.

Please do not introduce fish, even a few goldfish. They will clear frogspawn and dragonfly nymphs within weeks and the pond will never recover its wildlife value.

Planting for Wildlife — and What to Avoid

Plant in three zones: submerged oxygenators, marginals, and a flowering fringe. Native species are far more useful to invertebrates than double-flowered garden varieties.

• Submerged: hornwort, water starwort and curled pondweed, anchored in baskets of low-nutrient loam.
• Marginal: marsh marigold, water forget-me-not, flowering rush, water mint and purple loosestrife. Yellow flag iris is lovely but spreads — keep it in a basket.
• Floating: a single native white water lily, contained, for shade and cover.

Leave roughly a third of the surface clear so birds can land and bats can drink on the wing. Then guard against the thugs. New Zealand pygmyweed, floating pennywort, parrot's feather and water fern will smother a small pond in a single season, and all are subject to legal restrictions on sale and spreading. Never transfer water, weed or silt from a neighbouring pond without checking it first, and never release terrapins or non-native fish.

Helping Creatures In and Out

Access is everything. Set a shallow pebble beach at one end, sink a few large stones as stepping platforms, and lay a piece of roughened timber from the bank into the water as an escape ramp. Push a log pile and a stone cairn into the long grass nearby for frogs, newts and overwintering insects.

Resist the urge to tidy the margins. Dragonflies need emergent stems to climb when they emerge from their nymph cases, and seed heads left standing feed birds through the winter.

Coastal Sites and Ongoing Care

Within a mile or two of the sea, salt-laden wind shapes what will thrive. Use a filtered shelter belt of hawthorn, blackthorn or sea buckthorn rather than a solid fence, which simply creates turbulence. Avoid any hollow that takes sea spray or tidal flooding, and top up from rainwater rather than a brackish ditch.

Maintenance is light if you resist interfering. Net or rake fallen leaves before they sink, hand-pull blanketweed in summer, and cut back marginals in late autumn while leaving some stems standing. Never use dyes, algaecides or barley-straw substitutes without reading the label carefully. Expect the pond to look its best in its second or third year — the first season is always a little raw. Give it time and it will repay you every spring.