England's traditional front gardens are under threat, with a third already paved over in some regions, according to Natural England.
Paving front gardens 'reduces havens for wildlife'
The conservation body is urging businesses, councils and the public to help by leaving areas unpaved.
In London alone front gardens covering an area 22 times the size of Hyde Park are covered up reducing havens for wildlife, it says.
A manifesto is being signed by wildlife organisations later in London.
Research by MORI found that in north-east England 47% of front gardens were paved, 31% in south-west England, 30% in eastern England and 25% in the East Midlands and in north-west England.
The manifesto follows an ICM poll, commissioned by Natural England, in which 45% of 18-34 year olds said they were not well-informed about wildlife gardening.
The poll also found that 37% of 18-24 year-olds said they would like to do more but do not know how.
Sir Martin Doughty, chairman of Natural England, said: "The gardens of England are under threat.
"In London, front gardens with a total area 22 times the size of Hyde Park [12 square miles] are now paved over and lost, reducing havens for wildlife, increasing the impact of flash flooding and contributing to climate change.
"Through this manifesto, Natural England is calling on businesses, the public sector and the public to play their part and give gardens a future, for the benefit of our own health and the survival of declining species that live on our doorsteps."
Natural England said gardens acted as a "supermarket" for visiting and breeding animals and were the places where most children had their first contact with the natural world.
Joan Ruddock, minister for biodiversity, said: "This manifesto will help to improve gardening advice to encourage people to manage gardens in a way that benefits wildlife."
The manifesto is being signed at Roots and Shoots, in Lambeth, south London, a global community programme for young people interested in making a positive change in communities, for animals and the environment.