A Pond for the Smallest Plot

You do not need half an acre and a hired digger to bring wildlife into your garden. A pond of a single square metre, sunk into a sunny corner, will be discovered within weeks by frogs, newts, damselflies and a dozen species of water beetle. In a country that has lost the great majority of its natural ponds over the past century, garden ponds have quietly become one of the most valuable habitats we can offer. Even a half-barrel lined with butyl will do more for local wildlife than a manicured lawn ever could.

The secret is to get a handful of details right from the outset. Sort the position and the lining properly, plant it with natives, and the pond will largely look after itself.

Choosing the Right Spot

Position is the mistake you will regret fastest, so give it proper thought before you lift a spade.

• Away from trees. This is the single most important rule. Falling leaves rot down and turn the water into a stagnant, nutrient-rich soup, and by autumn you will be netting it out every weekend. Tree roots will also push at the liner from below, and the shade cast by a mature canopy will stunt the flowering plants you need. Keep a good three or four metres clear of any established tree, and remember that roots travel further than you think.
• Sun for most of the day. Aim for at least five or six hours of direct light. Warm water teems with life; cold, shaded water sulks.
• Level, open ground. A gently sloping site is manageable, but a truly level patch saves you endless fiddling with the liner edge. Avoid the lowest point of the garden, where rainwater will flood the pond and wash in nutrients from the lawn.
• Somewhere you will see it. A pond visible from a kitchen window gets watched, and a watched pond gets cared for. It is also far easier to spot a heron before it makes off with your frogs.

Digging: Shape, Depth and That All-Important Slope

Mark out a curving, irregular shape with a length of hosepipe or a rope, then cut the turf and stack it to one side for re-use. Dig in stages rather than all at once. Leave a shallow shelf roughly twenty to twenty-five centimetres deep around part of the perimeter for marginal plants, then take the centre down to between sixty and seventy-five centimetres. That depth keeps the water cool in summer, stops it freezing solid in winter, and gives frogs and newts somewhere to overwinter in the silt.

The detail most people miss is access. A pond with sheer sides is a death trap for hedgehogs, voles and any small creature that wanders in for a drink. Leave one section with a gentle slope, no steeper than about thirty degrees, running from the water's edge down to the shelf. If your design will not allow it, build a ramp instead: a run of evenly spaced stones, a piece of roughened timber, or a bundle of twigs secured at the edge. Anything a small animal can grip will do.

Finally, check every part of the hole with a spirit level and a straight edge, and remove any sharp stones, glass or jagged roots.

Lining with Butyl

Forget cheap polythene, which perishes in a season or two, and think twice about rigid pre-formed moulds, which crack and offer a poor shape. Butyl rubber liner is the material to buy. It is flexible, frost-proof, resistant to ultraviolet light and, in a garden pond, will comfortably last thirty years or more.

To work out the size you need, take the maximum length, add twice the maximum depth, then add a further half a metre for an overlap around the edge. Do the same for the width. Order the next size up rather than cutting it fine.

Underneath the liner, lay a protective underlay. Old carpet with the hessian backing, thick cardboard and purpose-made geotextile all work well, and it is worth the extra effort: a single sharp flint pressed against butyl for a decade will eventually find its way through. Line the hole, press the butyl into the shelves and corners rather than forcing it, and allow it to settle before you trim anything.

Planting with Native Oxygenators

Fill the pond with rainwater from a butt rather than the tap, which carries phosphates and nitrates that encourage algae. Once it has stood for a week, plant up. Use aquatic baskets lined with hessian and filled with low-nutrient loam rather than multipurpose compost, which will feed the algae rather than the plants.

• Oxygenators: hornwort, water starwort and spiked water milfoil. These live below the surface, absorb nutrients directly from the water and keep it clear. Half a dozen bunches is ample in a small pond.
• Marginals: marsh marigold, water mint, purple loosestrife and lesser spearwort will clothe the shelf and give insects somewhere to climb out.
• A floating plant or two: white water lily in a modest variety, or frogbit. Do not let them cover more than a third of the surface.

Resist the temptation to add fish. They eat spawn, stir up silt and turn clear water green.

Filling, Settling and Aftercare

Dress the overlap with turf and paving, leaving one low edge for visitors to approach. Then leave the pond alone for a fortnight or so before expecting much; new ponds look raw, and they cloud over briefly while bacteria establish. Within a month you should see pond skaters and the first damselflies. Keep the leaves out in autumn, top up with rainwater in dry spells, and cut back dead growth in early spring rather than autumn, so that any creature sheltering in the stems has moved on. A single afternoon's work, and years of interest.