He took a new role at the RHS last year but remains in charge at its showpiece garden. His expanded role involves providing support and advice to the curatorial teams at the four RHS gardens, along with advising the charity on horticultural standards. He will retain overall responsibility for the horticultural development of Wisley.
He says: "You have to have individualism at each garden. It's important to have an overview." He will not manage staff at the other gardens.
Staffing at Wisley has been an issue during the recent restructuring — more than expected took voluntary redundancy leading to 30 jobs needing to be filled. But Gardiner says there are three good applicants for every job going at Wisley.
He sees the loss of staff, mostly to voluntary redundancy, in the last few months of last year as a chance for new blood to make its mark in horticulture. What is more, Gardiner says those who have left are hot property in the horticulture market, in a large part because they have received such good training and gained such top-quality experience at Wisley.
"Why do you want to stand in people's way if they want to move on?" he asks. "No-one has stood in my way in the past. These are people with great talent. We have trained them extremely well and they have become highly-desirable horticulturists in the marketplace."
The restructure aims to cut seven layers of curatorial management. There will be three new garden managers, 12 new team leaders and four specialist roles.
Ninety staff look after the garden, which is currently hosting a butterfly festival in its 2007 bicentenary glasshouse. Last year the 1,300 butterflies (hatched from chrysalises from Stratford Butterfly Farm) brought in 130,000 visitors in six weeks. Wisley signed up 11,000 new members in 2009 - a good result in a tough year.
Gardiner says: "The glasshouse was value for money and was a huge success. It has really improved visitor numbers and has given us great opportunities to display plants that require tender and tropical environments that you don't really see anywhere."
He says 80 suppliers link in with the displays to provide plants for sale in the Wisley plant shop. "Linking the plant centre and suppliers and displays is very important."
One of Gardiner's triumphs is the Oudolf border, planted in the 1990s before Piet Oudolf became the complete star of perennial planting that he is today. The 140m double border "caused a few ripples" among members at the time, Gardiner admits.
With gardens by Oudolf, Tom Stuart-Smith and James Hitchmough nearby, the glasshouse has opened up the 80ha site for more people to see "hidden gems" such as the arboretum and new and developing children's play area. Hal Moggridge's masterplan from almost 20 years ago identified the site for the garden - one of the beauties of the RHS is that it can call on the best in their fields, says Gardiner.
He likes the mix of the old and the new in the garden, which the masterplan helps to bring together. The rock garden is a century old in 2011. "The beauty of the garden is the mix of historical and good recent plantings as well."
On the horizon is Robert Myer's rose garden, which runs down in terraces from the 1960s Bowes Lyon pavilion. Growers Harkness and Austin are advising on which roses to plant. Gardiner says the gardens, paid for by Witan Investments, will have much in place by next winter. They will include a structure of yew and Gardiner's beloved magnolia and paths made from Bradstone stone.
After the rose garden, Gardiner wants a new edible garden on the 3,000sq m site of the former glasshouse, which has been demolished and cleared. This development counters committee members (see analysis, p14) who are concerned about vegetable trial numbers and staff being rundown this year. The garden will depend on outside funding, which the RHS has not yet found.
"The masterplan identified the edible garden as a big aim," he says. "The site has considerable potential."
Talking of edibles, in response to vegetable trial members concerns about cuts in numbers of plants trialled, Gardiner says: "We spend substantial sums of money - £500,000 a year - on trials. We're the only independent doing it - we're not behoved to a particular trade. We have the voice of authority when giving the Award of Garden Merit (AGM). Hand on heart, we say this is the best we can recommend."
He adds: "You have to have a strong back. Every organisation is going to get criticism but we want to achieve excellence. The difficulty in the past with trials is that sometimes we're putting AGMs back onto the trial fields again and again and again. There is a huge plethora wanting to be assessed. We want them all to have a fair crack of the whip but we don't have unlimited resource to do it."
1968-73 Trained at Askham Bryan College, York, University of Cambridge Botanic Garden and Savill & Valley Gardens, Windsor
1973-80 Garden supervisor, Royal Botanic Garden, Edinburgh - looked after scientfic collection and propogation unit
1980-84 Curator, City of Liverpool Botanic Garden
1984-88 Curator, Sir Harold Hillier Garden & Arboretum, Hampshire
1988-2009 Curator, RHS Wisley
2009-date Chief curator, RHS