Part of a Worthing car park will be closed for around 23 weeks, the borough council has confirmed.
Contractors are moving in on Monday to start a £1million project and space is needed for the workers and their equipment.
One half of the Highdown Hill car park, the area nearest to Highdown Gardens, will have to be closed as part of the programme.
The work, paid for by the National Lottery Heritage Fund, will help preserve the world-famous gardens for future generations.
A spokesman for Worthing Borough Council said: “We realise this might be an inconvenience for walkers on the hill but it should not be for long and, of course, the prize will be the re-opening of the gardens in late summer with new facilities like the visitors’ centre and a sensory garden, and more facilities to manage the fragile plant collection.
“We hope everyone will see that the temporary closure will be for the benefit of these beautiful gardens.”
The closed area of the car park will allow work offices and building equipment to be safely housed. When ground conditions allow, the overflow car park will be open to deal with extra capacity.
The gardens themselves, and the public toilet block, are already closed for the project.
Work includes building a greenhouse to help the propagation and preservation of extremely rare plants from around the world, building a visitors’ centre, exploring and digitising the archive and creating new accessible walkways.
The 8.5acre gardens are internationally important as they are home to hundreds of rare plants and trees uniquely grown on chalk soil.
The aim of the project is to preserve the gardens, which were planted by Sir Frederick Stern and have been cared for over the past 50 years by Worthing Borough Council, as sole trustee of the Highdown Tower Garden and Pleasure Ground charitable trust.