Why a pond earns its place

If you do only one thing for wildlife in a small garden, make it a pond. A hole in the ground holding a metre and a half of water will out-perform a bird table, a bug hotel and a wildflower strip put together. Frogs and toads arrive to breed and then spend the summer eating slugs in your borders. Dragonflies and damselflies hunt midges over the surface. Blackbirds, robins and sparrows come to drink and bathe, and on warm evenings you may catch a bat skimming the water for insects.

It does not need to be big, and it does not need to be a project for a landscaper. If you can spare a weekend and a patch of lawn roughly the size of a dining table, you have room for a proper wildlife pond.

Choosing the spot

Aim for somewhere that gets sun for at least half the day. Sun warms the water, which brings on the insects that everything else feeds on, and it lets marginal plants flower properly. Full shade tends to produce a cold, lifeless pond.

• Keep clear of deciduous trees. Falling leaves rot down and turn the water sour, and roots can puncture a liner. A metre or two beyond the branch spread is ideal.
• Avoid the lowest corner of the garden. Runoff from paths and beds carries nutrients and, potentially, weedkiller. A pond fed by rich run-off will spend its life smothered in blanketweed.
• Think about cover. Frogs and newts feel far safer with a hedge, log pile or long grass nearby to retreat into.
• Check before you dig. Look at where drains, water pipes and cables run. If in doubt, dig a test hole by hand rather than going straight at it with a spade.
• Be honest about children. A shallow, gently sloping pond is far safer than a steep-sided one. If you have toddlers, either fence it or wait a year or two, and always supervise.

Digging and shaping

Mark the outline with a hosepipe or a length of string — an irregular, curvy shape settles into a garden far better than a rectangle. Then dig in stages rather than trying to hit the final depth in one go.

Build in two levels. A shallow shelf around the edge, about 10–15 cm deep and 25 cm wide, is where your marginal plants will sit. The centre should go down to 45–60 cm, which is deep enough to stay unfrozen at the bottom in a hard winter and gives frogs somewhere to shelter.

Most important of all: leave one side as a gentle ramp, sloping gradually from the water up to dry ground. Amphibians, hedgehogs and thirsty birds all need an easy way in and out. A steep-sided pond is a trap, and a frog that cannot climb out will drown.

Keep the turf you lift — stacked upside down it makes a decent edging. Remove sharp stones and any thick roots, and firm the sides as you go so they do not slump.

Lining and filling

For a small pond, a butyl or EPDM liner is the most forgiving option. Buy a sheet generously larger than you think you need — allow for the depth and at least 30 cm of overlap all round. Lay down a geotextile underlay, or a good layer of sand topped with old carpet, so nothing underneath can pierce it.

Run the liner into a shallow trench around the edge, fold it neatly and bury it. Hide the exposed edge with turf, stones or gravel, and let plants grow over it.

Fill with rainwater from a water butt if you can. Tap water contains nutrients and chlorine, which will give you an algae bloom in the first few weeks. If you must use tap water, let it stand for a few days before planting and expect a green phase — it passes.

Leave the water level 5–8 cm below the rim, so heavy rain does not wash everything out and so creatures can move in and out easily.

Planting it up

Plant in late spring or summer, when the water is warm. Stick to native species and avoid anything sold as vigorous or invasive — never introduce floating pennywort, New Zealand pygmyweed or parrot's feather.

• Marginals (on the shelf): marsh marigold, water forget-me-not, lesser spearwort, yellow flag iris, water mint.
• Oxygenators (submerged): hornwort and water starwort. These keep the water clear.
• Floating: a small native water lily such as Nymphaea pygmaea, or frogbit. Keep them to a third of the surface; too much shade and the pond goes dull.

Plant into baskets of loam-based soil, topped with gravel to stop it clouding the water. Add a few stones and a small log at the edge for shelter. Do not add fish to a small wildlife pond — they eat everything else.

Looking after it through the year

The first season will look alarmingly green. Leave it alone. As plants establish they take up the nutrients the algae are living on, and the water clears.

Cut back excess oxygenators in summer so that at least a third of the surface stays open. In autumn, do not tidy the pond to death: leave seed heads, hollow stems and a log pile nearby for overwintering insects, frogs and newts. Do your main cutting back in spring, not autumn.

Resist moving frogspawn from other ponds. Disease spreads easily that way, and a healthy garden pond colonises itself. Expect insects within weeks, frogs the following spring, and dragonflies within two or three years. Then simply sit back, mug in hand, and watch.