Why frogs make a pond work better

There is something deeply satisfying about the first clump of frogspawn appearing in a cold February corner of the garden. Common frogs are among the most rewarding creatures to welcome into a British pond, and they repay the favour generously: a single adult will take slugs, beetles, flies and other garden nuisances throughout the warmer months. Frogs are also a good sign of water quality. If they thrive, chances are the whole pond is in fine health.

The trick is to give them damp, sheltered, chemical-free conditions, then be patient. Frogs often find a new pond within a season or two, particularly if there are already damp corners and long grass nearby.

Design the pond with frogs in mind

Frogs need three things from the water itself: shallows to spawn in, deeper water to retreat to, and an easy way out. Aim for at least one gently sloping side or a shallow shelf around 10–20 cm deep, where adults can sit half-submerged. In the middle, a depth of 60 cm or more helps the pond stay unfrozen at the bottom in a sharp winter and keeps the water cooler in summer.

Edges matter as much as depth. Steep, hard-sided ponds trap wildlife, so build in a ramp: a length of rough timber, a slab of stone or a pebbled beach will do. Frogs will use it, and so will hedgehogs, birds and the occasional toad. Position the pond where it gets a mix of sun and shade — a few hours of sunshine helps plants and insects, while dappled shade over part of the surface keeps the water from overheating.

Size matters less than shape. A small, irregular pond with plenty of edge is better than a large, straight-sided one. Even a barrel or half-buried trough can work, provided it has a shallow lip and a way out.

Keep the water clean and chemical-free

This is the single most important rule. Frogs have permeable skin and absorb whatever is in the water, so anything designed to kill is bad news.

• Use rainwater from a butt rather than tap water wherever possible. If you must top up from a tap, let it stand or use a dechlorinator.
• Keep fertilisers, weedkillers and lawn treatments well away. Run-off from a treated lawn can wipe out a season's tadpoles.
• Never use slug pellets near a pond. Metaldehyde and similar poisons kill frogs, toads and hedgehogs.
• Avoid fish. Goldfish and other fish eat spawn and tadpoles, and their waste clouds the water. A wildlife pond should be fish-free.
• Take care with pumps and filters — fit guards so tadpoles are not drawn in.

Plants that do the heavy lifting

Native plants give adults cover, shade the water to keep algae in check, and offer surfaces for insects to land on. Around the margins, marsh marigold, water forget-me-not, water mint, brooklime and ragged robin all earn their place. In the water itself, try hornwort, water starwort and curled pondweed, with a native water lily if the pond is large enough. Avoid invasive non-natives such as parrot's feather or floating pennywort, which can swamp a small pond within a season.

Do not be too tidy. Leave fallen leaves in the bottom, leave some vegetation standing over winter, and if you must clear the pond, do it in late spring or autumn and leave the debris at the edge for a day so any creatures caught up in it can return to the water.

Shelter, shade and somewhere to overwinter

A pond alone is not enough. Frogs spend most of their lives out of the water and need cool, damp cover close by. Long grass, a wild corner, log piles, a stone heap, dense ground cover and compost heaps all make ideal refuges, as do gaps beneath sheds and thick shrubs.

Frogs have a habit of turning up in odd places — a window well, a dry drain, the bottom of a watering can. If you find one somewhere unsuitable, move it gently to damp cover nearby.

Looking after your frogs through the year

Frogs tend to return to the pond where they were born, so once you have a population, look after it. Spawning usually happens between late January and March, depending on where you are in the country. Tadpoles take around twelve to sixteen weeks to metamorphose, and froglets leave the water in summer, often on damp, rainy days. They are vulnerable until they find cover, so keep long grass and log piles right up to the pond edge.

In winter, keep part of the pond free of ice with a floating ball or a small pond heater, and never smash the ice — the shock waves can harm frogs resting in the mud below. Avoid moving spawn or frogs between ponds, as this spreads disease.

Then all you have to do is wait. A pond that is damp, shady, chemical-free and full of insects will not stay frogless for long — and the chorus on a mild evening in early spring is worth every bit of the effort.