The Gardening Against The Odds Awards were given out at Syon House in London 22 April.
The judges, who included David Bellamy, Christopher Woodward and Tim Richardson, wrote: "Waverley Terrace Allotments is now a thriving community resource helping offenders, socially excluded adults and those with mental illness to make a contribution to their community by gardening in these productive allotments and sensory gardens."
Organiser Conservation Foundation founder David Shreeve said: "This is a community garden in the true sense of the words."
The awards, founder in memory of the late gardening writer Elspeth Thompson, are open to individual gardeners and community groups all over the country who garden against the odds to create beautiful spaces that enrich their own life and the lives of those around them.
Meanwhile, the Conservation Foundation presented a yew tree propagated as part of an HLF-funded We Love Yew project, to the Duchess of Northumberland.
The project launches in May 2015 to commemorate the 800th anniversary of the signing of the Magna Carta at the Ankerwyke Yew at Runnymede. Yews propagated from ancient trees will be distributed as part of the project.
Hayloft Plants and Carbon Gold are among backers of the awards.