Just 29 per cent of people taking part in this year's annual wildlife survey for BBC Gardener's World Magazine had seen a hedgehog in their garden in the last year, down from 32 per cent the previous year.
Only one in 10 (11 per cent) of the 2,348 of the people who took part in the survey said they saw the hedgehog regularly in their gardens and 48 per cent had never seen one.
Hedgehog populations are down 30 per cent since 2003 to less than a million in the UK - down from estimated populations of 36 million in the 1950s.
The survey suggests people are keen to save the species, immortalised by Beatrix Potter as Mrs Tiggy-Winkle and a friend to gardeners as it feeds on pests such as caterpillars and slugs.
More than half (52 per cent) said they wanted to save hedgehogs from extinction, beating other at-risk British species such as the sparrow, puffin, mistle thrush and hairy footed bumblebee.
And seven out of 10 people said they would be happy to cut a hole in their garden fences to allow hedgehogs to roam more freely to help halt their demise.
Lucy Hall, BBC Gardener's World editor, said: "The much-loved, humble hog is among gardeners' most appealing natural allies, but they're disappearing on our watch.
"And yet a few simple steps, from leaving out the right food, to opening up gaps in fences and creating secluded areas for nesting and hibernation, will help make our gardens the havens that hedgehogs have long enjoyed.
"If we act collectively now, we can still help save the species for future generations, but time is running out."
The magazine has drawn up a list of tips to help save hedgehogs, including planting hedges, cutting holes under fences, making ponds safe, not using slug pellets, leaving out dog or cat food but avoiding bread and milk which can kill hedgehogs, and checking bonfires before lighting them.