Is it OK to run a robot mower at night?

Most robot mowers can mow in the dark, but in the UK you shouldn't let them. The main reason is hedgehogs.

Hedgehogs forage on lawns at night, and when threatened they curl up rather than run. Research led by Dr Sophie Lund Rasmussen found that robot mowers can injure them and that the mowers tested needed physical contact to detect one. Hedgehog Street, run by the British Hedgehog Preservation Society and People's Trust for Endangered Species, advises running robot mowers in daylight only. Frogs, toads and other small animals are also most active around dusk and after dark.

Cameras and LiDAR on newer mowers are aimed at obstacles such as toys, shoes and pets. No manufacturer we know of publishes independent evidence that its mower avoids hedgehogs, so a detection claim is not a reason to mow at night.

Two practical points follow:

• Set the schedule for daylight with a margin after sunrise and before dusk, and move it as the evenings draw in. Check that any rain-delay feature can't push a session into the evening.
• Size the mower so it doesn't need the night. If it can only keep up by running round the clock, it is too small for the lawn. A mower with a rated area comfortably above your lawn size will finish in daytime hours.

Daytime mowing is also kinder to neighbours, since some mowers are noticeably loud. Our hedgehog and wildlife guide covers schedules in more detail.