Creating a wildlife pond in a small seaside plot

Why a small pond earns its space

Even a plot the size of a couple of parking spaces can hold a genuinely useful wildlife pond. On the coast, where gardens tend to be sandy, windswept and free-draining, standing fresh water is scarce and precious, and anything that holds it through a dry summer becomes a magnet. Frogs, newts, damselflies, diving beetles, pond skaters and a steady traffic of birds will find it, usually within a season.

The most important decision is the one that surprises people: leave the fish out. Goldfish, and even small native fish, will clear a tub pond of tadpoles and invertebrate larvae within weeks. Fish waste also feeds algae, so the water turns green and the planting struggles. A fishless pond is a wildlife pond; the two are not the same thing.

Siting it: salt, wind and sun

Salt is the coastal gardener's constant companion, but direct spray is rarely the main problem for a pond. The real risk is salty run-off draining off paths, decking, a salt-treated fence or a gravelled drive after a storm. Site your pond slightly above the surrounding ground rather than in the lowest corner of the garden, and avoid anywhere that visibly floods in winter.

Wind matters too. A tub in the full blast of a prevailing south-westerly will be stripped of leaves and constantly topped up with grit. Tuck it behind a hedge, a low wall or a slatted fence — but not so enclosed that it never sees the sun. Aim for at least half a day of sunlight, ideally morning sun with a little afternoon shade, because dragonflies need warmth to hunt and display.

Keep clear of overhanging trees, whose leaves will smother a small pond and whose roots will puncture a liner, and away from anywhere you routinely mix fertiliser or wash down paving.

Sinking the tub or liner

• Choose a container with 45–60cm of depth. An old bath, a lined half-barrel, a rigid preformed liner or a butyl liner set into a dug hole all work well. Depth matters because frogs and newts overwinter in the bottom mud, and a pond that freezes solid can kill them.
• Dig the hole slightly wider and deeper than the container and cushion the base with 5cm of sharp sand or soft soil.
• Check the rim is level, then part-fill with water before backfilling. The weight settles the tub and reveals any tilt while you can still correct it.
• Backfill with soil, firming as you go, and leave the rim 2–3cm proud of the surrounding ground so run-off cannot sheet in. Edge it with gravel.
• Build a gentle ramp at one end: a stack of stones, a piece of rough timber or a gravel shelf just below the surface. Hedgehogs, frogs and fledgling birds all need a way out, and a steep-sided tub is a death trap.
• Fill with rainwater from a butt where you can. Tap water is acceptable in an emergency, but it carries nutrients that encourage algae.

Planting for a windswept, salty spot

Plant marginals in baskets of ordinary garden loam topped with gravel — not potting compost, which fuels algae. Good native choices for a small pond include water forget-me-not, marsh marigold, lesser spearwort, water mint, ragged robin and bogbean. Yellow flag iris is handsome but vigorous, so keep it confined to a basket. For oxygenators, hornwort and water starwort are reliable and need no planting at all.

Avoid floating pennywort, parrot's feather, water fern and New Zealand pygmyweed — all invasive, all capable of smothering a small pond, and illegal to plant in the wild. Duckweed is best kept out from the start, as it will blanket a tub in weeks.

Around the rim, use coastal-tolerant plants that shrug off salt and wind: sea thrift, sea campion, lady's bedstraw and hardy geraniums. Add a small log pile or a patch of long grass nearby, and frogs will have somewhere damp to sit out the heat of the day.

Keeping the water clean and fishless

A small pond has no margin for error when it comes to nutrients, so treat the area around it as a chemical-free zone. No fertiliser, no weedkiller and no slug pellets within a few metres, and never wash a car or pressure-wash a patio where the run-off can reach the water.

Top up with rainwater rather than the hose. Scoop out excess fallen leaves in autumn, but leave a few for the invertebrates that shelter among them. Never empty and scrub a pond — that destroys the entire community in one afternoon. If it genuinely must be cleaned, do it in early autumn and leave the sludge at the edge for a day so creatures can crawl back in.

Let the water settle for a fortnight before planting. Cloudy water in a new pond is normal and usually clears on its own as the plants establish.

What will arrive, and how little to do

Frogs and newts will find you. Damselflies and dragonflies follow — common darters, broad-bodied chasers and southern hawkers all use surprisingly small water. Pond skaters, water boatmen and diving beetles appear as if from nowhere. Sparrows, blackbirds and robins will drink and bathe if you provide a shallow gravel shelf, and yes, they will also eat some of the larvae. That is part of the bargain.

Resist the temptation to move frogspawn in from elsewhere; disease and invasive plants travel with it, and wildlife is perfectly capable of arriving under its own steam. Leave plant stems standing over winter so dragonfly larvae can climb out, and don't tidy in autumn. If the surface freezes, float a ball to allow gas exchange, and melt a hole with a pan of hot water rather than smashing the ice, which sends a shock wave through the water. Otherwise, the kindest thing you can do for a seaside pond is very little at all.