Meanwhile, RHS director general Inga Grimsey left her role last week ahead of schedule to have an operation on her foot. Grimsey resigned from the RHS in September but was expected to stay until Christmas. Deputy director general Gordon Seabright has taken over the running of the society.
Gardiner's expanded remit includes providing support and advice to the curatorial teams at the four RHS gardens, along with advising the charity on horticultural best practice in all its activities. He will retain overall responsibility for the horticultural development of Wisley.
RHS director of gardens and estates Jill Cherry said: "Jim has an international reputation as a leader in the world of horticulture, and this new role will enable the RHS to benefit more broadly from his expertise. The introduction of new team structures at our gardens means that Jim will be able to step back from some of his operational responsibilities to help hone the horticultural excellence and leadership that underpins everything we do."
Gardiner said: "I'm absolutely delighted to take on this wider role at a time when we have so many exciting developments at the RHS gardens. I look forward to working closely with my fellow curators and colleagues across the RHS to continue to build on the great horticultural heritage that is the bedrock of the RHS."
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