Environmental biologist Ross Cameron, from the University of Reading, said that gardens have a range of social, physical, environmental and even psychological benefits and should be given the same protection as virgin countryside.
He insists that UK gardens must be protected against a wave of "garden-grabbing" developers.
He added an estimated 32 sq km (7,900 acres) of gardens had been lost in London alone in the past five years as developers tried to build more homes on green spaces.
Cameron said studies with patients suffering mental health problems also showed that gardens helped to reduce stress.
He also warned that "garden-grabbing" could even "cost lives" if it exacerbates depression and other conditions.
"A recent report from Australia suggests gardening helps delay the onset of dementia in the elderly," Times Online quoted Cameron as saying.
"There is evidence from a study in Chicago that areas with greater greenery have less crime. The greatest reduction was in domestic violence, a stress-related crime," he added.
Green spaces could also help to cool cities as climate change warmed up our urban environments.