The competition, now in its third year, is open to designers and students aged 28 and under and three winners will build their gardens at the RHS Flower Show Tatton Park.
Show manager Kris Hulewicz said: "This gives young designers a platform to launch their career." The finalists will be announced at the RHS Chelsea Flower Show next May and receive a £12,000 grant.
SGD chair Annabel Downs said: "The competition is a fabulous opportunity for garden designers to compete alongside their future contemporaries."
The deadline for submissions is 6 January 2012.