Making a wildlife pond in a small garden

Why a small pond earns its space

Few garden features repay the effort as quickly as a pond. Within days of filling, water boatmen and pond skaters appear as if from nowhere, and damselflies are often not far behind. Frogs, common frogs and smooth newts will find it within a season or two, and if you plant it generously, dragonflies such as the common darter and broad-bodied chaser may start breeding in it. Even a sunken basin no bigger than a large bath can become the busiest square metre in your garden.

The reason is simple: in much of the UK, standing fresh water has become scarce. Field ponds have gone, ditches are often dry or polluted, and garden ponds now form a genuine network of stepping stones for amphibians and insects. Your patch does not need to be grand. It needs to be wet, chemical-free, and easy for wildlife to get in and out of.

Choosing the right spot

Position matters more than size. Aim for somewhere that gets sun for perhaps five or six hours a day, with shade for part of it. Full sun all day encourages blanketweed, while deep shade discourages flowering plants and keeps the water cold and sluggish. A spot that is sunny in the morning and dappled in the afternoon is close to ideal.

Try to avoid:

• Overhanging trees. Leaves and fruit rot down and feed algae, and roots can puncture a liner.
• The lowest point in the garden. Runoff carries soil, fertiliser, and any weedkiller you have used, all of which will harm pond life.
• Right beside a boundary fence if you can help it, so you can reach all sides for planting and maintenance.

Also think about children and pets. A pond is a wonderful thing for a family, but a shallow shelf and a firm, visible edge are sensible precautions. If you have toddlers, consider a raised or half-barrel pond with a sturdy planted margin instead of a ground-level one.

Digging and lining the basin

A useful shape is a simple oval, roughly 1.5 metres by 1 metre, with a gentle slope down one side and a deeper section of about 45 to 60 centimetres. That depth keeps part of the pond unfrozen in a hard winter, giving frogs somewhere to overwinter. Anything deeper is unnecessary in a small garden; anything much shallower risks drying out in a hot July.

Mark the outline with string or sand, then dig in layers, creating a shelf about 20 centimetres deep around much of the edge. This shelf is where your marginal plants will sit, in baskets or straight into the soil-free substrate.

Once dug, remove sharp stones, line the hole with a 5 centimetre layer of soft sand, and lay a protective fleece over that. A butyl liner is the most durable choice, but a decent preformed shell is quicker and easier if your shape is straightforward. Let the liner rest for a day, then fill slowly with rainwater — the weight of the water will settle it neatly into every contour. Trim the excess, leaving 20 to 30 centimetres to tuck beneath stones or turf at the edge.

Planting a native pond

Plants do three jobs: they oxygenate the water, shelter invertebrates, and shade the surface so algae cannot take over. Work in layers.

• Marginals for the shallow shelf: marsh marigold, water mint, water forget-me-not, lesser spearwort, ragged robin, bogbean.
• Oxygenators for the deeper water: hornwort and water starwort, both native and unfussy about shade.
• Floating plants for surface cover: frogbit or a small amount of water lily in a larger basin.

Two or three bunches of oxygenators and half a dozen marginals will fill a small pond surprisingly fast. Avoid yellow flag iris and bulrush, which are lovely but thuggish in a confined space, and never plant anything invasive such as parrot's feather or water fern.

Filling, and then leaving it alone

Rainwater from a butt is far better than mains water, which is nutrient-rich and can trigger an algae bloom. If you must use the tap, fill the pond and let it stand for about a week before planting. Please do not add fish. Goldfish and sticklebacks will eat tadpoles, larvae, and everything else that makes the pond interesting.

Then do almost nothing. A new pond often turns green for a few weeks before plants establish and grazers arrive. Do not empty it and scrub it clean. Leaf litter and a little sludge are habitat, not mess. If you ever need to clear it, do it in late September or in spring, and leave anything you scoop out on the edge for a day so creatures can crawl back.

Making it safe and easy for wildlife

The single most important detail is access. Frogs, newts, and hedgehogs can all drown in a steep-sided pond, so provide a way out. Pile stones or bricks into a shallow ramp at one end, or run a piece of roughened wood from the water to the surrounding soil. A shallow gravel beach on one side serves the same purpose and gives birds somewhere to bathe.

Around the edge, leave a wilder margin: a few clumps of long grass, a small log pile, and some stones. Adult frogs and newts spend most of the year on land and need damp cover nearby, while dragonfly larvae climb stems to emerge as adults. Resist the urge to tidy right up to the water's edge. A little untidiness is exactly what makes a small pond work.