When do hedgehogs hibernate, and what to do in your garden now

Hedgehogs in the UK usually hibernate from around November to March or April, though some start in October and the exact dates depend on the weather. In a mild autumn they stay active into November and December, and through the winter they wake and move nests. So a hedgehog seen in January isn’t necessarily wrong, but one out in daylight is.

There is no fixed start date. Hedgehog Street puts it at “October/November through to March/April”. The Wildlife Trusts say “November to mid-March”. Both are describing the same thing. Hibernation follows the weather, not the calendar, and a mild autumn pushes it later.

They don’t sleep straight through

Hibernation isn’t one long sleep. Hedgehog Street says research shows each hedgehog “is likely to move nesting sites at least once” during the winter, and that during mild winters they “can remain active well into November and December”. Its autumn advice adds that hedgehogs “will wake from time to time during hibernation”.

In practice that means two things for a garden. A hedgehog might be using your log pile in December and someone else’s hedge bottom by February. And a mild night in the middle of winter can bring one out to look for food and water, which is why the food and water you put out in autumn is worth continuing in mild spells. A shallow dish of fresh water costs nothing, and Hedgehog Street’s line is that it “will be appreciated by any hog out and about”.

Waking up is expensive, though. Hedgehog Street warns: “Do not disturb hibernating hedgehogs as it may cause them to stir and use up valuable energy reserves.” The fat a hedgehog built up in summer and autumn has to last until spring. Every time it is disturbed, it uses up some of that.

Where they hibernate

A hedgehog doesn’t hibernate in the open. It builds a nest, called a hibernaculum, and the British Hedgehog Preservation Society (BHPS) describes it well. In autumn hedgehogs “collect dry leaves, grass, bracken, reeds etc.” and pack them into a nest that is “surprisingly waterproof and good insulation against the cold”. In the wild they build “at the bottom of hedgerows, fallen logs or piles of brushwood”. In a garden, the BHPS lists “gaps under sheds, compost heaps, shrubs and piles of leaves”.

The BHPS leaflet doesn’t mention bonfire piles, but its other guidance makes it clear that a hedgehog sees a heap of prunings the same way it sees a log pile: as shelter.

That is the whole case for leaving some of the garden untidy. Hedgehog Street’s A to Z puts it simply: “brambles, log piles, leaf piles and long grass or scrub are all perfect places for hedgehogs.” A hedgehog needs dry leaves to build a winter nest, and a garden that has been raked bare has none. More on that in leave the leaves, and if you want to give them a purpose-built home, see our guide to hedgehog houses.

What to leave alone this winter

Leaf piles, hedge bottoms and log piles. Rake leaves off the lawn if you need to, but pile them under a hedge or in a quiet corner rather than bagging them all. Whatever you don’t leave for hedgehogs can go into a leaf mould cage. Leave hedge bottoms and log piles alone until spring.

The compost heap. The BHPS says to “take care when turning the heap; one thrust of a fork can easily kill more than one baby hedgehog”. It gives “probably Oct/Nov” as the safest time to spread a heap, after most young have left their mothers and before adults start hibernating. By late November that window is closing. Our advice is that if you haven’t emptied the heap yet, leave the middle of it until spring, and take compost from the edge. The BHPS’s rule is “always check first”.

Bonfire piles. A pile built a week ago is a nest site by now. Build it on the day you light it, or move the whole pile to fresh ground first, and light it from one side only. The full check is in our bonfire hedgehog check. Better still, compost or shred the material and skip the bonfire altogether.

Long grass and wild corners. If you do a last cut, check by hand first. The BHPS poster’s rule is “Look before you cut.”

Sheds and garages. The BHPS lists gaps under sheds as nest sites, so leave that space alone. Keep shed and garage doors shut and anything poisonous out of reach.

If you uncover a nest by accident, the BHPS’s advice is to put the nesting material back over it and leave it alone. Don’t let anyone lift it again “for a peep”. If you’re worried, ring the BHPS on 01584 890801.

The small hedgehog in late autumn

Some hedgehogs are born late in the summer and never put on enough weight. The BHPS calls them “autumn juveniles”: “old enough to be away from their mothers but too small to hibernate successfully”. It says this season can start as early as September and is busiest through November.

The tier-1 sources do give weights, and they broadly agree:

• Hedgehog Street: hedgehogs “can successfully hibernate at a minimum weight of 450g, but are more likely to survive hibernation at 600g”.
• BHPS: from the end of October, a hedgehog under 450g “may need rescuing, depending on weather and other circumstances”; one under 250g in autumn is likely a genuine orphan and should be rescued straight away.
• RSPCA: if you can’t weigh it, compare it to fruit. Under about 300g is roughly apple-sized. Over 450g is bigger than a mango.

Two more things matter as much as the weight. The BHPS says a hedgehog out in the daytime in autumn or winter probably needs rescuing even if it seems lively, because it “can be days away from death”. The same goes for a cold, curled-up hedgehog found outside a proper nest.

Whether a particular hedgehog needs to be taken in is a call for a rescue, not for us, and not for a weight chart alone. If you see a small one, or any hedgehog out in daylight, ring the BHPS on 01584 890801 and they will put you in touch with a local carer. Our guide to a hedgehog out in the day covers the signs and who to call.

The honest bit

The broad picture is well established: hibernation from roughly late autumn to spring, with waking and nest-moving in between, in leaf nests in sheltered spots. The exact dates aren’t, because they depend on the weather and on the individual hedgehog, and the charities give slightly different months. The weights are the charities’ working thresholds from rescue experience. They are useful guides, not hard cut-offs, and the BHPS itself says the decision also depends on the weather and other circumstances. Our advice to leave the middle of the heap alone once winter sets in is our reading of the BHPS’s timing, not a direct quote. More on the animal itself is on our hedgehog profile.