Making a simple wildlife pond from a half barrel

Why a half barrel makes a fine pond

A half barrel holds 90–110 litres, which sounds modest but is ample for a small colony of frogs, newts, water boatmen and damselflies. Because it stands above ground, there's no digging, no clay to barrow away and no risk of putting a fork through a buried liner. It suits a courtyard, a balcony with a solid floor, or the shady corner where nothing else will grow.

It is also forgiving. You can move a barrel if the position proves wrong, reach into it without wading, and start again if the first attempt fails. That makes it the ideal first pond.

Choosing and siting the barrel

Look for a genuine oak half barrel, the sort sold as a planter, around 60–70cm across at the top. Avoid anything that has held oil, chemicals or creosote, and give a newly made barrel the sniff test: if it reeks of preservative rather than wood, walk away. Untreated oak that once held whisky or sherry is perfect, because the staves have been soaked for years.

If the barrel has been standing dry, fill it with water and leave it for a fortnight so the wood swells and the hoops tighten. A little dribbling is normal at first, and most barrels continue to weep slightly even after swelling — one good reason to line it anyway.

Site it where it gets five or six hours of sun a day and where no tree will shower it with leaves. A little shade in the afternoon is a bonus, as it keeps the water cooler and holds back the algae.

Lining the barrel and building a way out

A one-metre square of butyl or EPDM liner is usually enough. Drape it loosely inside rather than stretching it, fold the excess neatly over the rim, and hide the edge behind the top hoop or a strip of half-round timber.

The ramp matters more than most people realise. A frog can climb a rough, wet surface, but nothing can scale a smooth vertical wall, and a hedgehog or a fledgling that tumbles in will drown without an exit. Set a piece of rough stone, a log or a small stack of bricks at a shallow angle from the bottom to just above the water line. Good options include:

• A weathered log weighted at the base
• A staircase of stones built up one side
• A coil of rough rope or hessian draped over the rim
• A shallow pebble shelf sitting just below the surface

Fill the barrel with rainwater from a butt if you can. Tap water will do at a push, but it carries nutrients and chlorine that feed algae.

Planting it with native species

Three or four plants will do more good than a crowded display. Aim for a mix of oxygenators, which grow submerged, and marginals, which sit in shallow water at the edges.

Reliable natives include marsh marigold for gold flowers in April, water forget-me-not for a long season of small blue blooms, and water mint for scent and late nectar. Ragged robin enjoys a damp margin too. Among oxygenators, hornwort and water starwort are unfussy and need no basket of mud at all.

Grow marginals in aquatic baskets lined with hessian, using proper aquatic compost rather than garden soil, and top each basket with grit so the soil doesn't cloud the water. Stand the baskets on bricks so the crown of each plant sits at the depth it likes — roots wet, leaves above the surface.

Two warnings. Never introduce floating pennywort, Australian swamp stonecrop or water fern: all are invasive and illegal to plant in the wild. And resist adding fish, which eat the tadpoles and larvae that make a pond worth having.

Keeping the water clear without chemicals

The first spring is always the worst. Expect pea-green water and a flush of blanketweed as the pond finds its balance, and don't panic. It usually settles by midsummer once the plants have grown and the microscopic life has caught up. Twirl blanketweed out with a cane and leave it on the edge for a day so any trapped creatures can crawl back in.

Never use algicides on a wildlife pond, and top up with rainwater rather than tap water. Clear fallen leaves promptly in autumn, before they sink and rot, and let the submerged oxygenators do the rest.

What turns up, and seeing it through winter

Be patient, then be surprised. Frogs often find a new barrel within weeks if there's a pond nearby; newts take longer. Damselflies and dragonflies arrive to lay eggs, pond skaters and water boatmen appear from nowhere, and bees and hoverflies use the wet edges to drink. Leave a stone breaking the surface and birds will use it as a bath.

In autumn, cut back only what flops into the water and leave the rest standing — hollow stems shelter insects through the cold, and seed heads feed birds. Never empty and scrub a pond as you would an aquarium. If the barrel freezes, float a ball on the surface to keep a hole open, and never smash the ice, which sends shock waves through the water.

Every two or three years the baskets will need dividing and a little silt removing in early spring, before the frogs get busy. Beyond that, a half barrel stocked with natives asks almost nothing of you — which is, on balance, the best thing about water in a small garden.