Why a small pond earns its keep

A pond is the single most valuable habitat you can add to a cottage garden or smallholding, and it does not need to be big. Per square metre, a wildlife pond supports more species than a border, a lawn or a hedge put together. Within a season you can expect pond skaters, water beetles, damselflies and at least one frog. Give it two or three years and newts will usually find it, followed by dragonflies.

There are practical rewards too. Frogs and their tadpoles eat slugs, snails and other garden pests by the hundred. Thirsty birds — especially in a dry July or a hard January frost when every other water source is frozen — will use a shallow pond daily. Hedgehogs, which lose a great deal of condition to dehydration, need a drink far more often than most of us realise. All of that from a hole in the ground roughly the size of a dining table.

Choose the right spot and the right shape

Aim for part sun and part shade. Six hours of sun keeps flowering plants happy and encourages dragonflies, but some afternoon shade keeps the water cooler and reduces the algae that thrives in warm, bright water. Avoid the lowest point in the garden, where run-off brings in nutrients, and avoid sitting the pond under trees — leaves rot down, and roots will find any liner.

Before you dig a spade in, check for buried cables, pipes and soakaways. Then think about shape. The two features that matter most are a gentle slope and varying depths:

• A deepest point of about 60–70cm. This stays liquid in a hard frost and gives frogs somewhere to overwinter.
• Wide shallow margins of 10–30cm. Most pond life lives here, and shallow water warms up quickly in spring.
• Sloped sides, never vertical. Anything that falls in must be able to climb out. A straight-sided pond becomes a death trap for hedgehogs and beetles.
• A pebble beach at one end. A gentle ramp of smooth stones gives birds and mammals a safe place to drink and bathe.

Digging and lining

Mark the outline with a length of rope or a hose, then dig in stages, keeping the topsoil on a sheet for reuse. Cut a shelf about 20cm down around the perimeter, then dig the deeper central section. Remove sharp stones and roots, and line the hole with 2–3cm of soft sand, or old carpet and underlay, to protect the liner from punctures.

Butyl or EPDM liner is the best choice — thick, flexible in cold weather and long-lasting. To work out how much you need, take the longest length plus twice the depth plus 60cm, and do the same for the width. Lay it loosely and let it settle into the contours rather than forcing it flat, then fill slowly. Rainwater from a water butt is ideal; tap water carries nutrients that feed algae. Leave the overhang for a fortnight before trimming, so the liner can stretch as the ground settles, then tuck it into a shallow trench and cover with turf, soil and stones. That hidden edge looks natural and gives amphibians a foothold.

Plant natives, and plant generously

Native plants do the heavy lifting: they oxygenate the water, shade out algae and provide cover and egg-laying sites. Aim for roughly half the surface covered by floating leaves, leaving open water for birds and hunting dragonflies.

• Oxygenators: hornwort, water starwort, curled pondweed.
• Floating: frogbit, water soldier, a small native water lily — not a vigorous cultivar.
• Marginals: marsh marigold, water forget-me-not, water mint, brooklime, ragged robin, lesser spearwort, purple loosestrife and yellow flag iris, which needs room.
• Around the edge: creeping jenny, meadowsweet, lady's smock and native grasses to soften the rim.

Never plant floating pennywort, water fern, parrot's feather or New Zealand pigmyweed. These are invasive and cause real harm if they escape. Never take plants from the wild either, and never move frogspawn between ponds — it spreads disease and hitchhiking invasives.

The three rules: no fish, no pump, no chemicals

Fish eat tadpoles, newt larvae and almost every insect that makes a pond interesting, and they foul the water. A wildlife pond should have none. Pumps and filters are equally unnecessary; frogs, newts and dragonfly nymphs all prefer still water. There is no need for chemical treatments or barley straw either.

Keep fertiliser, pesticides and slug pellets well away, and leave a buffer of rough grass around the pond so any run-off is filtered before it arrives. Resist topping up with tap water — collect rainwater instead.

Looking after it through the year

Leave the pond entirely alone over winter. Do any clearing in late autumn, while amphibians are still active and before hard frosts. Lift excess leaf litter with a net and leave it on the bank for a day so anything caught can crawl back. Keep about a third of the surface clear of plants so the water stays open. Top up with rainwater, and never empty or scrub the pond out — the murk is the ecosystem.

Pile logs and stones nearby as cover, and let the grass grow a little longer around the edge. Then be patient. The first spring will bring water beetles and pond skaters; frogs often arrive within a season; newts and dragonflies will follow. It is one of the few garden projects that gives more back each year than you put in.