Alan was born in Ilkley Moor in Yorkshire, England. He has appeared in an advert for the Yorkshire Tourist Board in a series which included contributions from other Yorkshire-born celebrities including Brian Blessed, Melanie Brown, Darren Gough and Brian Turner.
After gaining a City and Guilds in Horticulture, Alan went on to study at Oaklands in Hertfordshire for the National Certificate in Horticulture. He then gained the Kew Diploma after training at the Royal Botanic Gardens, Kew. He worked as a horticultural journalist for a number of publications, including Amateur Gardening (magazine), where he was the deputy editor. He has written over 30 gardening books and four novels. His autobiography, Trowel and Error (ISBN 0340765429) was published in 2002.
Between 1996 and 2002, Alan hosted the popular show Gardeners' World. He presented Ground Force, a garden redesign program, between 1997 and 2002, where in one episode he worked on the garden of Nelson Mandela. He won his first Gold Medal at the Chelsea Flower Show in 1985 for a country kitchen garden design. His waxwork was added to Madame Tussauds in 2000.
Alan is married to Alison and has two daughters named Polly and Camilla.