The sitters in the order they appear on the montage:

Bunny Guinness Garden designer, author and panelist on Gardeners' Question Time
Nigel Colborn Gardening expert, author, journalist, broadcaster and blogger
Bob Flowerdew Organic gardening expert, author, panelist on Gardeners' Question Time
Emma Townshend Author, journalist, lecturer and blogger
Joe Swift Garden desiger, author, journalist and TV presenter on Gardeners' World
Adam Pasco Garden expert, journalist, editor of Gardeners' World Magazine
Cleve West Award winning garden designer, gardening expert, author, broadcaster, blogger
Rosie Atkins Curator at Chelsea Physic Garden, author, journalist
Stephen Lacey Broadcaster, author, journalist, garden designer
James Alexander-Sinclair Broadcaster, author, journalist, garden designer, blogger
John Cushnie Garden designer, author, journalist, panelist on Gardeners' Question Time
Arabella Lennox-Boyd Award winning garden designer
Alan Titchmarsh Television presenter, gardening expert, garden desiger, author, journalist
Beth Chatto One of the foremost gardening experts in the UK, author
Rachel de Thame Garden desiger, author, journalist and television presenter
Matthew Wilson RHS Garden designer, gardening expert, author, TV presenter
Matthew Biggs Gardening expert, author, journalist, panelist on Gardeners' Question Time
Barbara Collecott RHS archivist, Librarian for RHS Gardens
Jim Gardiner Curator of the RHS Garden at Wisley
Jim Arbury Fruit Superintendent at RHS Wisley, gardening expert
Guy Barter Head of Horticultural Advice at the RHS
Andrew Lawson Garden photographer, author
Dan Pearson Award winning garden designer, author, TV presenter
Juliet Roberts Author, journalist, editor Gardens Illustrated Magazine
Mary Keen Author, journalist, garden designer
Tania Compton Author, journalist, garden designer
Pippa Greenwood Garden expert, author journalist panelist on Gardeners' Question Time
Professor Stephen Hopper Director, Royal Botanic Gardens, Kew
Dr Nigel Taylor Head of Horticulture, Kew
Tony Kirkham Head of the Arboretum at Royal Botanic Gardens, Kew
Chris Beardshaw Award winning garden desiger, author, journalist and TV presenter
Jekka McVicar Organic gardening expert, nurserywoman, author, journalist and broadcaster
Carol Klein Gardening expert, nurserywoman, author, TV presenter on Gardeners' World
Roy Lancaster Foremost plantsman in the UK, plant hunter, TV presenter, author, journalist
Alys Fowler BBC gardener, journalist and TV presenter on Gardeners' World
Toby Buckland Gardening expert, author, presenter on Gardeners' World
Fergus Garrett Plant expert, author, journalist, lecturer and Head Gardener at Great Dixter
Andy Sturgeon Award winning garden designer, gardening expert, author, broadcaster
John Brookes One of the foremost garden designers in the UK
Marina Christopher Plant expert, nurserywoman, lecturer, author, journalist
Judy Medhurst Expert nurserywoman
Peter Catt Expert nurseryman
Ann-Marie Powell Garden desiger, author, journalist and TV presenter