Why frogs and toads need a helping hand

By late October, most of the frogs and toads in a British garden have disappeared from view. They are not gone — they are tucked away somewhere cool, damp and frost-free, waiting out the winter in a state of torpor. Their body temperature drops close to that of the surrounding air, their heartbeat slows, and they live off the fat reserves they built up over the summer. Get it wrong and they freeze; get it too warm and they burn through those reserves before spring arrives.

In the wild, amphibians would use mammal burrows, cracks in old stumps, dense log piles and the deep litter at the base of hedgerows. Modern gardens are tidier than that. A hibernaculum — simply a mound of logs, stones, twigs and leaves — puts that habitat back, and it takes an afternoon to build.

Choosing the right spot

Frogs and toads are particular about where they settle. Pick a spot that catches sun for part of the day, ideally facing south or west, and is sheltered from the worst of the wind by a hedge, fence or shrub. Ground that sits wet all winter is a poor choice; amphibians want damp, not waterlogged. A gentle slope or slightly raised bed drains better and stays a degree or two warmer.

• Put it within a few metres of a pond, but never in the pond itself — common frogs often overwinter in mud at the bottom, where oxygen can run short, so a land-based refuge is the safer bet.
• Leave rough grass, leaf litter and tussocks around it, so animals can approach without crossing open ground.
• Keep it well away from the bonfire pile, any compost heap you turn regularly, and paths you use in winter.
• Once built, treat it as permanent. An amphibian woken from torpor in January uses up energy it cannot easily replace.

What you will need

You should not need to buy anything. A hibernaculum is a deliberate mess, built from whatever the garden already produces.

• Logs, thick branches and sections of trunk, ideally with the bark still on.
• Rubble, broken bricks, stone and gravel for drainage.
• Twigs, prunings, dead herbaceous stems and hedge trimmings.
• Leaf litter, grass cuttings and a little moss.
• The soil you dig out of the hole.
• Optional: a short length of pipe, or a few flat stones, to make an entrance tunnel.

Building it, step by step

1. Dig a shallow saucer. Mark out a patch roughly 1.5 to 2 metres across and dig a bowl 30 to 40 centimetres deep. Keep the soil to one side on a tarpaulin.

2. Add drainage. Spread a 10-centimetre layer of rubble, gravel or broken bricks across the base. This keeps the interior from flooding.

3. Build the tangle. Lay logs across the rubble in a loose criss-cross, leaving plenty of gaps. Fill the spaces with stones, twigs and a scattering of soil. The aim is a labyrinth of damp crevices at different levels, not a solid stack.

4. Create an entrance. Angle a short piece of pipe, 10 to 15 centimetres in diameter, from the outside down into the middle, or leave a tunnel of stacked stones. Toads in particular like a walk-in burrow.

5. Cap it with litter. Pile leaves, grass cuttings and moss over the top, then cover the mound with 15 to 20 centimetres of soil, leaving the entrance clear.

6. Firm and water. Press gently, water it in well so everything settles, and scatter a few more leaves on top. A little bugle or wild strawberry around the edge will knit it into the border.

Looking after it

The mound will sink as the material inside rots, which is exactly what you want; decaying wood and leaves generate a little warmth and help keep the interior above freezing. Top it up with a fresh layer of leaves each autumn. Avoid cutting it back, strimming near it or forking it over at any point between October and March.

In summer the same structure works all over again: slow worms, beetles, centipedes and the occasional grass snake will use it for basking and shelter. After five to seven years, when it has collapsed into a low mound of leaf mould, rebuild it in late spring — once the last amphibian has moved on.

If you are short of space

A small garden can still do its bit. Sink a sturdy crate or a large pot with drainage holes into a quiet corner, fill it with logs, stones and leaves, and leave a pipe entrance at the side. Stack a few logs against a hedge, pile leaves around the base, and leave them there rather than tidying them away. Even a modest log pile, a stone wall with gaps in it, or an undisturbed patch of long grass gives a toad somewhere to spend the winter — and a toad in the garden is worth its weight in slugs come June.