The King and Queen are to tour a “No Adults Allowed” garden at the Chelsea Flower Show on Monday.

Charles, the new patron of the Royal Horticultural Society (RHS), and Camilla are to go ahead with the annual royal visit as the King continues with a flurry of public duties while he undergoes treatment for cancer.

They will meet growers and horticulturalists and explore The RHS No Adults Allowed Garden – the first in the history of the show to be designed by children, for children.

But the King and Queen will have to make a special pledge to gain access, if they stick to the strict rules set by the pupils from Sulivan Primary School in Fulham, south-west London, who worked on the project with garden designer Harry Holding.

Initially there was only one rule for adults: they were not allowed to enter.

But Clare Matterson, director-general of the (RHS), said she had secured entry for grown-ups after some “tough negotiating”.

The children agreed adults can tour the garden if they pledge to do one of three things – either plant a tree, donate to RHS Campaign for School Gardening or find a flower that starts with the first letter of their name.

To gain access to the garden, the King and Queen are expected to have to share their pledge, receiving a sticker designed by the children in return, which permits them to enter.

The No Adults Allowed garden is described as a “joyful journey through a fantastical landscape where children can explore the magic of lush woodland, bountiful meadows and a wetland with heightened colour and fun oversized bog plants”.

The King and Queen will tour Chelsea, accompanied by the Duke and Duchess of Gloucester, the day before the annual horticultural celebration opens to the public.

Royal visits to Chelsea have been a regular fixture in the royal calendar for many years.

Charles and Camilla will also see the Addleshaw Goddard Junglette Balcony Garden, where hardy tropical planting has been used to mirror the structural layers of a jungle.

And they will visit the Moroto no IE Garden, by Kazuyuki Ishihara, which features vibrant acers and a tumbling waterfall to “blend the beauty of the natural world with the practicalities of family life”.

The King has succeeded his mother Queen Elizabeth II as the RHS’s patron, a role she held for 70 years, after a review of royal patronages following her death.

Charles is a passionate gardener, who spent more than 35 years transforming the garden at his Highgrove home in Gloucestershire.

Ms Matterson said: “It means the world to the RHS and our wider horticultural family of growers, nurseries, gardeners, designers and plantspeople that Their Majesties The King and Queen, accompanied by The Duke and Duchess of Gloucester are visiting RHS Chelsea again this year.”

She said she hoped they would enjoy the “spectacular displays” and “hopefully, as us gardeners love to do, sharing some top gardening tips and getting lots of inspiration along the way”.

The visit is the latest in a number of official appearances for Charles since his return to public duties after his cancer diagnosis.