The new, accessible facility was made possible thanks to a £25,000 donation from the Morrisons Foundation.
Residents at Chailey Heritage Foundation joined Lewes MP Maria Caulfield, Chailey County Councillor Matthew Milligan and Community Champions from local Morrisons stores at the opening event.
Chailey Fundraising manager Will Folkes said: "This garden has been in need of a makeover for a while so we were so grateful to receive a grant from the Morrisons Foundation.
"We have transformed the area into a colourful and accessible new space which our residents can use to relax, socialise, and practice their wheelchair driving skills."
A section of concrete has been removed to make way for AstroTurf and a new canopy now covers much more of the area to provide shade. New planters have also been installed alongside sensory sculptures.
Maria Caulfield MP said: "I had a great afternoon visiting the new garden space at Chailey Heritage.
"It was great to see the young people having a lovely time with the new equipment, and I know that they and the staff are very happy with the new space.
"I want to pay tribute to the Morrisons Foundation who made this possible with their very generous grant and for all the work that the staff at Chailey Heritage do to support the young people."
Brighton Community Champion for Morrisons Louise Coffey said: "We are absolutely thrilled to be supporting Chailey Heritage Foundation, and the makeover looks amazing.
"Morrisons is committed to supporting the local community and important projects in each town and village."
David Scott, Morrisons Foundation Trustee said: "I'm delighted that we've been able to help Chailey Heritage Foundation develop this wonderful outdoor space which will provide many opportunities for young people with complex needs to enjoy outdoor activities for many years to come."
Chailey Heritage Foundation is a charity providing education, care and transition services to children and young adults with complex physical disabilities. Their mission is to give disabled children and young adults every opportunity to pursue their fullest potential.