This is the first time the RHS has worked with a partner to exhibit at every RHS show in a season, starting with RHS Show Cardiff at Bute Park from 20 to 22 April.
Design will showcase some of the most challenging urban environments where gardening and community work brought people together for social good, he said.
"The green space around us - where we live and work - has a fundamental effect on our emotions and behaviour," he said.
"Whatever the green need there is a solution and contrary to popular belief it doesn’t have to mean high cost - The Urban Oasis Gardens showcase design that can make a difference in people’s lives."
He explained the key message was to challenge people to think about how they could preserve a cherished green space or get stuck in and create their own oasis for the wider community.
Sue Biggs, RHS director general, said: "We are teaming-up with Groundwork to champion the benefits of gardening in urban communities.
"Community gardening is important to society and while regeneration of urban areas is transforming lives and livelihoods all over the country.
"We need to shout about this, and what better platform to do it from, than our magnificent flower shows."
Groundwork chief executive, Sir Tony Hawkhead, said: "Urban green spaces have become a powerful catalyst for change."
Richard Gillies, a director at Marks & Spencer, said: "This is a fitting way to mark Groundwork’s 30th year. We’ve worked with the charity for four years.
"Its employees and volunteers are often the unsung heroes of local communities. The work they do transforms urban green spaces.
"We’ll be encouraging as many of our customers and employees as possible to get down to the RHS shows."