Attracting Bats to a Mature Garden

Why Mature Trees Do the Heavy Lifting

If your garden has a mature oak, ash, beech or even a well-grown old apple, you already own the single most valuable bat habitat on the street. Old trees offer what tidy modern gardens rarely do: lifted bark, rot holes, storm cracks, dense ivy and standing deadwood. Pipistrelles, our commonest garden bats, will squeeze into a gap no wider than two fingers. Brown long-eared bats want something roomier, while noctules prefer the high canopy. Add a decent hedge, a pond and a patch of long grass and you have the makings of a genuinely good bat garden.

Everything that follows comes down to three things: somewhere to roost, darkness to travel through, and clean water to drink. Get those right and the evening shift will find you.

Putting Up a Bat Box That Actually Gets Used

A box on a mature tree is not a substitute for a natural roost, but it is often the quickest way to bring bats in close enough to watch from a kitchen window. Position matters far more than price.

• Height and clearance: fix it between three and five metres up, with a clear flight path in and out. Avoid branches that would snag a bat's approach, and keep it away from dense climbers.
• Aspect: a box facing south to south-west warms up early, which bats like in spring. But a south-facing box can overheat in a heatwave. Offer a cluster instead — two or three boxes on the same tree or neighbouring trees, facing different ways, so the colony can move with the weather.
• Materials: rough-sawn untreated timber or woodcrete, a durable mix of concrete and wood fibre. Never use treated timber, creosote or paint inside. A narrow crevice of 15–20mm suits pipistrelles; deeper, roomier chambers suit long-eared and Natterer's bats.
• Mounting: strap or bracket the box to the trunk rather than nailing into it. Nails open wounds in a tree you want to keep for decades, and the strap can be loosened as the trunk grows.
• Patience: bats are creatures of habit. A new box may sit empty for a season or two before it is found. Leave it where it is rather than shifting it about every few months.

Turning Down the Lights

Artificial light is the quiet killer of a good bat garden. A single dusk-to-dawn security light can delay emergence by an hour or more and make an entire commuting route unusable. Pipistrelles tolerate light better than most, but brown long-eared, Daubenton's, Natterer's and whiskered bats will simply avoid a lit garden altogether — and those are the species worth working for.

• Swap dusk-to-dawn lights for motion sensors with a short run time of a minute or two.
• Choose warm-white, low-output fittings of 2700K or lower, mounted low and pointing down.
• Fit hoods, shields and cowls so the beam stays on the path and does not spill into the canopy or across the pond.
• Light paths and patios only when they are in use. Leave the rest of the garden genuinely dark.
• Draw curtains after dusk — indoor light spills outdoors just as badly as a security lamp.

Water Is the Evening Draw

Bats drink on the wing, skimming low over open water, so a clean pond is one of the best investments you can make. Even a small raised barrel pond topped up with rainwater will do.

• Keep the approach over the water open and uncluttered. Don't ring the whole pond with tall marginal plants.
• Rake off thick duckweed and blanket weed. A dense green carpet makes drinking difficult; chemicals make it worse.
• Never use pesticides, fertilisers or algaecides near water. Run-off destroys the insect life bats depend on, and polluted water can harm them directly.
• Include gently sloping edges and a shallow shelf, so birds and hedgehogs can drink and bat pups can practise.
• Top up from a water butt rather than the tap, and let the pond find its own balance.

Planting for the Insects They Hunt

A single pipistrelle can take thousands of small insects in a night. Garden for moths, midges, caddisflies and beetles, and the bats will follow the food.

• Grow night-scented plants: honeysuckle, evening primrose, jasmine, common knapweed, ox-eye daisy, foxglove and teasel.
• Let a patch of lawn grow long through summer and cut narrow paths through it.
• Leave log piles, leaf litter and standing deadwood in quiet corners — perfect nurseries for beetles and caddisflies.
• Keep or plant a native hedge of hawthorn, blackthorn or hazel as a commuting corridor between roost and feeding ground.
• Avoid insecticides and slug pellets. A garden with fewer chemicals simply has more bats in it.

Watching, and Knowing Your Limits

The best evenings are warm, still and mild — above about 10°C — in the first hour after sunset. Sit with your back to the last of the light and watch the gaps between trees. A modest heterodyne bat detector will tell you a great deal: pipistrelles come through at around 45kHz, soprano pipistrelles at 55kHz, and the slow, low slap of a noctule is unmistakeable.

Do remember that in the UK all bats and their roosts are protected by law. It is an offence to disturb a bat or damage or obstruct a roost, and that includes a box you bought and screwed to your own tree. Once a box is occupied, leave it alone. Never open it, never shine a torch inside, and if any tree work is needed, speak to a licensed bat worker before anyone picks up a saw.

Beyond that, the whole trick is patience. Put up the box, put out the light, keep the water clean, and give it two or three seasons. Mature trees took a lifetime to get that way, and the bats will come when they are ready.