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Why a Small Pond Works So Well by the Sea

Coastal gardens can feel like a tough crowd. Salt-laden wind scours the leaves, the soil is often thin, sandy or stony, and the growing season runs to its own peculiar timetable. Yet a pond is one of the most rewarding things you can add to a plot within earshot of the waves. Even a modest pool — a metre and a half across is plenty — becomes a magnet for wildlife that has few other places to stop.

Frogs and toads will find it within a season. Dragonflies and damselflies patrol it in summer. Birds use it for bathing and drinking, hedgehogs come for a nightly drink, and the insect life that gathers above the water feeds bats at dusk. Coastal ponds tend to be low in fish, which is good news: without fish, tadpoles and invertebrate larvae stand a far better chance.

The catch is that coastal conditions demand a bit more planning than an inland pond. Site it badly and you'll spend your summers topping up salty, wind-stripped water and fishing out shredded liner. Get it right and it will look after itself.

Choosing the Right Spot

Position is everything on an exposed plot. Work through these points before you pick up a spade:

• Shelter first. Avoid the side of the garden that takes the brunt of the prevailing wind. A hedge, a fence, a shed or even a dense shrub border will cut evaporation and stop spray blowing straight in.
• Avoid the lowest corner. In coastal gardens that dip often collects saltwater in storm surges or becomes a sump for waterlogged, brackish ground. Choose ground that drains, not the point where everything runs to.
• Aim for five or six hours of sun. Dragonflies and damselflies need warmth to hunt and to lay eggs, and flowering marginals will sulk in deep shade. A little afternoon shade is a bonus, as it slows evaporation.
• Keep clear of trees and foundations. Fallen leaves feed algae, and roots will eventually find a liner. Leave at least two metres between the pond edge and any building.
• Think about sightlines. A pond you can see from the kitchen window or a favourite bench will be watched far more often, and you'll spot problems early.

Digging and Lining

Mark out a shape with a hosepipe, then dig in layers. Aim for a central depth of 60–70cm, which gives frogs somewhere to overwinter and keeps the water cooler in a hot spell. Around the edge, cut at least one shallow shelf 20–25cm deep and 30cm wide for marginal plants and for creatures to clamber in and out. Add a gently sloping "beach" at one end — a ramp of stones or gravel — so hedgehogs, birds and amphibians can drink without drowning.

Line the hole with a generous layer of soft sand or old carpet, then a proper geotextile underlay, before laying butyl or EPDM liner. Buy more than you think you need; coastal wind has a habit of whipping loose liner about. Tuck the edges into a shallow trench, overlap them and weight them with turfs or paving, leaving a lip so rainwater and runoff don't carry soil straight in.

Never use concrete or cement rendering in a small wildlife pond — it raises the pH sharply and can leach for years. If you want a hard edge, use reclaimed bricks laid dry, or simply let the planting soften the rim.

Filling and Planting

Fill from a water butt if you possibly can. Tap water in many coastal areas is hard and nutrient-rich, which is an open invitation to blanketweed and green soup. Rainwater is soft, free and exactly what the plants want. If you must use the hose, let the pond stand for a fortnight before planting.

Then plant in three zones:

• Marginals on the shelf: water forget-me-not, brooklime, marsh marigold, water mint, lesser spearwort and ragged robin. These give cover, colour and perching points.
• Oxygenators submerged in the deep section: hornwort or spiked water-milfoil. Use baskets of aquatic compost topped with grit to stop it clouding.
• Edge and bank plants that shrug off salt: sea thrift, sea campion, yarrow and wild carrot, which knit the pond into the rest of the garden.

Steer clear of invasive thugs such as floating pennywort, water fern, parrot's feather and New Zealand pygmyweed. They can escape a small pond in a single summer and are a nightmare to remove.

Encouraging Wildlife to Move In

New ponds are colonised surprisingly fast, but you can speed things along. Leave a few stones and a log pile at the edge for frogs and newts to shelter under. Resist the temptation to introduce fish — they eat everything worth watching. Don't stock with frogspawn either; amphibians will find you, and moving spawn between sites risks spreading disease.

Allow some untidiness. Seed heads left standing over winter feed birds, and stems poking from the water are essential for dragonfly nymphs to climb when they emerge. A small patch of long grass or a wildflower strip nearby will bring in the insects that everything else depends on.

Looking After It Through Coastal Weather

Top up with rainwater during dry, windy spells, when evaporation from a small surface can be startling. Keep a float in the pond in winter so you can check it hasn't frozen solid, and gently melt any ice by resting a pan of hot water on the surface rather than smashing it, which harms amphibians. In autumn, net or rake out fallen leaves but leave them beside the pond for a day so anything caught up can crawl back. Clear only a third of the blanketweed at a time, and do your main tidy-up in September rather than spring, when the pond is at its busiest. A little patience and a sheltered spot are all it takes — within two years, your small coastal pond will be the liveliest corner of the garden.