Arnold, who was recently discovered to have small traces of "active cells" on his nose, said gardeners are high-risk because of working outside in summer. "But the spring is a vulnerable time too because there's lots of ultraviolet light around."
He added: "I'm the biggest coward in the world when it comes to going to the doctor but I'd say don't be a coward."
Gardeners should apply a high-factor sun cream, particularly on exposed areas such as ears and noses, he advised. They should also wear a hat and get moles checked, he added.
After 40 years as a gardener, Arnold has seen attitudes change to skin cancer. "Twenty years ago the only people who used sun cream were people who went on holiday to Spain. It was not macho to worry about the sun in those days."
New cases of malignant melanoma diagnosed in the UK in 2008 - almost 99,000
Non-melanoma skin cancers were also registered - 11,700