Rebecca Trewin
Why a half barrel makes a brilliant small pond
Most British gardens have at least one corner that does very little: a strip of shade beside the shed, a paved area behind the bins, a patch of gravel that never quite became a seating area. A half barrel fits there perfectly, and a pond of around 100 to 150 litres will pull in a surprising amount of wildlife within a season or two. Frogs, smooth newts, damselflies, pond skaters and water boatmen all use small water bodies, and birds will drop in to drink and bathe.
What a barrel gives you is depth without a huge footprint: roughly 40 to 45cm of water, which is enough for plants, insects and amphibians to breed, but too shallow and too warm for fish to thrive. That is a good thing. Please don't add goldfish. They eat tadpoles and frogspawn, their waste feeds algae, and they turn clear water into green soup. A barrel pond is at its best as a fish-free wildlife habitat.
One word of caution before you start: a barrel pond at ground level is a genuine drowning risk for toddlers and small pets. If you have young children, either fence the pond off or fit a sturdy rigid mesh grid just below the water surface. It still lets plants and wildlife through, and it keeps little ones safe.
Choosing and preparing your barrel
Old oak barrels turn up at farm shops, reclamation yards and garden centres. Whisky, port and wine barrels are ideal; steer clear of anything that has held oil, chemicals or creosote, and avoid barrels with unknown varnish or heavy treatment inside.
- Check for a bung hole and seal it with a cork and silicone, or a rubber bung.
- New barrels leak until the staves swell. Soak a second-hand barrel for a few days first, then see whether it holds water.
- Even a sound barrel is safer lined. A butyl or food-grade pond liner inside stops leaks, protects the wood from constant saturation and gives you a clean, inert surface for wildlife.
- Sit the barrel on a level, solid base: paving slabs or concrete blocks set into the ground. A full barrel is heavy, and if it tips you lose everything.
- Drill a small overflow hole a few centimetres below the rim, angled downward, so heavy rain doesn't flood plants out onto the path.
Siting it and filling with the right water
Choose a spot with at least four hours of sun a day for flowering marginal plants, but with some afternoon shade, which keeps the water cooler and slows algae. Avoid sitting it directly under trees: falling leaves decompose and feed algae, and the shade is usually too deep.
Fill with rainwater from a water butt if you can. Tap water contains chlorine and, more importantly, phosphates and nitrates that fuel algae. Letting tap water stand for a day or two helps with chlorine but not with the nutrients, so rainwater is genuinely worth the extra effort. Fill slowly, pouring onto a saucer or a sheet of plastic so you don't churn up the compost later on.
Planting with native species
Aim for roughly two-thirds of the surface covered in plants. Plant into aquatic baskets using proper aquatic compost, then cap the surface with washed gravel to stop the compost drifting and blackbirds flicking it everywhere. Use a mix of three layers:
- Oxygenators: hornwort and water starwort. These live below the surface, mop up nutrients and shelter tadpoles and newt larvae.
- Marginals: water forget-me-not, brooklime, marsh marigold and water mint. These sit on a shelf of bricks around 10 to 15cm below the water surface and give emerging dragonflies somewhere to climb.
- Floating and surface: frogbit is native and looks lovely, though it multiplies quickly, so thin it out. Native water lilies grow far too large for a barrel, so give them a miss.
Avoid the invasive non-natives entirely: floating pennywort, parrot's feather, water hyacinth and New Zealand pygmyweed. Several are illegal to sell or plant in the UK, and all of them will swamp a barrel in a single summer.
Ramps, stones and a way out
This is the part most people forget, and it matters more than the planting. Frogs, hedgehogs and beetles will fall in, and if they can't climb out they drown. Give them a gentle ramp at roughly 30 to 45 degrees, made from a weathered plank wrapped in hessian, a slate tilted into the water, or a stack of rough stones built up to the rim. Hessian and rough stone give claws and damp skin something to grip.
Then add a few flat stones around the edge, just breaking the surface. These become basking spots for insects, perches for birds, and landing pads for frogs. A shallow tray of pebbles at one end, kept wet by the pond, gives bees and hoverflies a safe place to drink.
Looking after it through the year
Expect green water in the first spring. It almost always clears as the plants establish and outcompete the algae, so don't reach for chemicals. Twirl blanketweed out with a stick, leave it on the path for a day so anything caught in it can crawl back, then compost it.
Top up with rainwater through dry spells, thin greedy plants in midsummer, and skim fallen leaves in autumn with a small net. Do leave a little leaf litter and some dead stems in the bottom over winter; frogs and dragonfly larvae overwinter in the silt. Resist the temptation to move frogspawn in from elsewhere, as this can spread disease between ponds. If you build it and plant it well, the wildlife will find it on its own.
