A hedgehog's night rarely ends at your fence. An adult can walk a kilometre or more between dusk and dawn, hunting beetles, earthworms, caterpillars and slugs as it goes. To find enough food — and, in spring and summer, to find a mate — it needs to roam across a patch of ground far bigger than a single back garden. In the countryside that means hedgerows and field margins. In towns and suburbs it means the network of gardens, allotments, churchyards and scraps of waste ground that we collectively own.

The trouble is that this network is broken. Solid fencing, gravel boards, brick walls and decking edges turn what should be a continuous habitat into thousands of small islands. A hedgehog that meets a barrier will often walk along it, sometimes for hundreds of metres, until it finds a way through — and that walk frequently takes it onto a road. Giving it a small, deliberate opening is one of the simplest and most effective things any gardener can do.

Why a Hedgehog Needs More Than One Garden

A single well-planted garden can be a wonderful place for a hedgehog, but it is rarely enough on its own. Hedgehogs are restless, wide-ranging animals, and a population only stays healthy if individuals can meet, mix and breed across a larger area. Isolated gardens slowly lose their hedgehogs and never gain new ones.

Connected gardens behave quite differently. A run of half a dozen joined-up plots — with a mix of long grass, borders, shrubs, log piles and a pond between them — can support several hedgehogs, and the animals move between them naturally, using fences and hedges as cover rather than crossing open tarmac. Numbers have fallen sharply in recent decades, so every link in the chain matters.

The Magic Measurement: Thirteen Centimetres

The gap you need is a square roughly 13 centimetres by 13 centimetres — about the size of a CD case, or a little wider than your outstretched hand. Hedgehogs are surprisingly flexible and can squeeze through smaller spaces, but 13 centimetres is the widely recommended size because it lets a well-fed adult through comfortably while still being too small for most dogs, cats and foxes to use as a thoroughfare.

There are several ways to create one:

• Cut a square notch out of the bottom corner of a fence panel with a saw or drill, then sand the edges smooth.
• Lift or shorten one gravel board at the base of a panel, leaving the gap underneath.
• Cut the bottom corner off a wooden gate, or leave a small opening beside a gate post.
• Remove a single brick at the base of a low garden wall, or leave a channel where a wall meets the ground.
• Where a fence sits on a concrete plinth, cut a notch through the concrete as well as the timber.

Whatever method you choose, make sure the hole goes all the way through, with no lip or step at the bottom that a hedgehog has to climb. A flat, clear passage at ground level is what you are aiming for.

Choosing the Right Spot for Your Gap

Hedgehogs prefer to travel along edges — the base of a fence, the line of a hedge, the foot of a wall — rather than crossing open lawn. Put your gap where it joins naturally onto cover, not in the middle of a bare boundary with nothing on either side.

Check what is on the other side before you cut. A gap that leads into a neighbour's patio, a driveway, or a garden with a pond with sheer vertical sides is less useful than one that opens onto a border, a rough grass edge or a compost heap. If you can, site two or three gaps in different boundaries so the route continues onwards rather than dead-ending.

Keep the approach clear once the gap is made. Trim back long grass or ivy that might block it, and check it after storms or heavy leaf fall. A quick yearly tidy in early spring, before the breeding season gets going, is plenty.

Linking Your Gap to Water and Shelter

Hedgehogs need water, especially in hot, dry spells when natural sources dry up. A shallow dish of fresh water at ground level is a lifeline, and it also makes your garden a more attractive stopping point on the route. If you have a pond, give it at least one gently sloping edge, a pebble beach, or a ramp of stone or rough timber so that any hedgehog that falls in can climb out. Steep-sided ponds and butyl-lined edges are a genuine hazard, and a few carefully placed stones can make all the difference.

Shelter matters just as much. A log pile in a quiet corner, a patch of long grass left uncut over winter, a leaf heap, or a purpose-built hedgehog house all give an animal somewhere to sleep, nest or hibernate. The best hedgehog gardens are slightly untidy ones — a little rough ground, some fallen leaves, and a few places where nothing much happens.

Keeping the Route Safe

A connected garden is only useful if it is also a safe one. Before you strim, mow or cut back a border, walk the area first and look for the distinctive rustle of a curled hedgehog. Check bonfire piles on the day you plan to light them, moving the material to a fresh spot if anything is nesting inside. Cover drains, and make sure nets and fruit cages are pegged down at ground level rather than left loose.

Food matters too. If you feed visiting hedgehogs, offer tinned meaty cat or dog food, or dry cat biscuits, and never bread and milk — hedgehogs are lactose intolerant and it makes them ill. Mealworms are best kept as an occasional treat rather than a staple.

Turning One Gap Into a Neighbourhood Highway

One gap is a start, but the real prize is a chain of them. Talk to your immediate neighbours, then the gardens beyond, and suggest each household cuts a 13-centimetre opening in a shared boundary. Six or eight linked gardens quickly becomes a genuine corridor, and a small sign or marker at each gap helps everyone remember why it is there.

Maps of hedgehog highways are now common in many neighbourhoods, and local wildlife groups are often happy to help spread the word. Even a single new gap this weekend is a step in the right direction — a small, quiet, thirteen-centimetre act of reconnection that a hedgehog will use tonight.