The five-year project redesigned and replanted the Centenary Border originally planted by Sir Harold Hillier in 1964 to celebrate 100 years of his family business.
Head of collections at the gardens David Jewell said: "This is our most ambitious project, which will help lead the gardens into the next 25-50 years."
Hillier Gardens has replaced 80 per cent of overgrown plants with new design combinations that it hopes will inspire visitors and provide ideas for their own gardens.
"As well as traditional perennial or woody plantings, there also are plenty of surprises including many plants that are new on the scene," Jewell added.
The border now has white granite paving for all-weather access and diagonal paths leading visitors to explore more of the world-renowned temperate plant collection.
The project involved landscape designer Julia Fogg Associates as well as the gardens' horticultural team and many of their 150 volunteers.
The Sir Harold Hillier Gardens is a charitable trust with remit in horticulture, conservation, education and recreation. The 180-acre site is managed and operated by Hampshire County Council.