Making a wildlife pond for rare aquatic plants

Why a garden pond punches far above its weight

Britain has lost something like three-quarters of its ponds in the past century, and with them a whole suite of plants that never quite fitted the modern landscape. Many of our rarest aquatics — floating water-plantain, pillwort, greater bladderwort, water violet — are not rare because they are fussy, but because they need exactly the sort of habitat we keep tidying away: small, sunlit, gently poached by livestock or churned by amphibians, and mercifully free of fish.

An ordinary garden pond of three or four square metres, dug properly and left alone, can hold species that have vanished from the surrounding parish. That is a genuinely remarkable thing to be able to say about a weekend's digging. What follows is the practical version: how to build it, what to plant, and the handful of rules that separate a thriving wildlife pond from a green soup.

Siting the pond: sun, safety and stray nutrients

Find a spot that gets direct sun for at least half the day. Shade suppresses flowering and encourages blanket weed; most rare aquatics want light on the water surface. Keep well clear of trees and large shrubs — roots puncture liners, and fallen leaves rot down into a nutrient load that will plague you for years.

• Avoid low corners. Run-off from paths, lawns and borders carries fertiliser, pesticide and silt straight into the pond.
• Leave a rough grass buffer of at least 30 centimetres around the edge to filter run-off and shelter amphibians.
• Think about children and neighbours before you dig. A pond 60 to 90 centimetres deep in the middle is safe enough for wildlife and manageable for plants, but it still needs supervising.
• Check for services before you start, and never dig where the ground is already waterlogged in winter — you will simply be digging a hole in a sump.

Digging and lining: the shape matters more than the size

Aim for a profile with shelves rather than sheer sides. A gently sloping "beach" on the north side gives amphibians, hedgehogs and thirsty birds a way in and out; without it, small creatures drown. Build one shelf at 20 to 30 centimetres for marginal plants, a second at 45 centimetres for deeper marginals, and take the centre down to 60 to 90 centimetres so the pond does not freeze solid or dry out entirely in a hot July.

Line with butyl or EPDM rubber over a geotextile fleece and a two-centimetre layer of soft sand. If you inherit a concrete pond, be prepared to seal it or line over the top — lime leaching makes it hostile to most plants. Fill from a water butt if you can. Tap water is not fatal in an emergency, but it arrives loaded with nutrients and phosphates, and you will pay for it in algae later.

Planting for rare and uncommon natives

Source plants from a specialist native-species nursery, and ask about British provenance. Never lift plants from the wild. Floating water-plantain, pillwort and starfruit are protected under Schedule 8 of the Wildlife and Countryside Act, and taking them is an offence. Nor should you introduce non-native aquatics — parrot's feather, water fern and New Zealand pigmyweed are all Schedule 9 species that can escape into the wider landscape.

Plant in spring or early autumn, using a loam-based substrate. No compost, no peat, no fertiliser — nutrients are the enemy.

• Submerged: hornwort, water starwort and common water-crowfoot. These oxygenate the water and give invertebrates somewhere to hide.
• Deep water: a modest native water lily, plus pondweeds such as Potamogeton natans.
• Marginals: lesser water-plantain, marsh marigold, water mint, flowering rush and sedges. These do the heavy lifting for insects.
• Floating: frogbit, now scarce in the wild, is a lovely choice for still water. Water soldier is vigorous — worth having only in a larger pond and only where it is locally appropriate.
• The specialists: water violet wants clean, base-rich water and will sulk in a new pond; give it two or three years before you judge it.

No fish, low nutrients, endless patience

Fish are the single most common reason a wildlife pond fails. They graze on young shoots, root up submerged plants, churn silt into the water column, eat tadpoles and invertebrates, and their waste delivers a steady nutrient drip. Goldfish are worse than koi. Ducks are almost as bad. Leave both out.

Equally, resist the urge to feed or fertilise anything. Do not top up with tap water if you can avoid it, and keep lawn feed, weedkiller and slug pellets well away from the catchment. A new pond will almost certainly turn green in its first spring. This is normal. Do not reach for a chemical fix — the algae subsides as plants establish and shade the water.

Looking after it, gently

Maintenance is mostly a matter of well-judged neglect. Leave the margins uncut over winter. Rake out excess duckweed by hand, net fallen leaves in autumn but leave a few for the invertebrates, and thin vigorous submerged plants every few years so light can still reach the water. If flag irises or sedges crowd the shelf, divide them in autumn and pass the spare plants on to a neighbour.

Then keep a record. Note what flowers, what fails, what arrives of its own accord — because a pond planted for rare aquatics rarely stays quiet for long, and the county records centre would very much like to know what turns up.