Rare roses and stunning irises are usually among the most coveted items at the Chelsea flower show. But this year, the star attraction might be pink, sequined – and decorated by David Beckham.

The former England football captain is co-designing a garden at the May event with King Charles and as part of that effort he has been given a garden gnome to paint. It will be auctioned off for charity.

Such a stunt would not have been possible in previous years: garden gnomes have been frowned upon since 1927, deemed “tacky” and not in keeping with the high-end aspirations of the event.

This year, the show has made a one-off decision to lift the ban to raise funds for the Royal Horticultural Society’s campaign for school gardening, an initiative to get children involved in horticulture.

It is unclear whether Beckham’s fashion designer wife, Victoria, has had any input into the gnome’s decoration. But as the former Spice Girl’s designs are generally minimalist and tasteful, this does not appear to be the case.

Beckham nodded and grinned when told by the RHS that he was free to use as many sequins and as much glitter as he liked on his gnome.

Surveying the primary-coloured paints he was given, he told them: “I might have to get some pink.”

Sources at the RHS said Beckham had spent days painting it and had met the king and the gardener Alan Titchmarsh at the royal residence of Highgrove last week to discuss their plans for the garden. Charles is said to have been keen for the gnome ban to be lifted so some could be displayed in the feature garden; he is a fan of the fairytale characters and has one in the grounds of his Gloucestershire estate.

They decided at this meeting to host a beehive in the garden, inspired by their enthusiasm for beekeeping and producing honey. The garden will include an easel created by Eleanor Pickin, a graduate of the Snowdon School of Furniture who met those involved in the garden design at Highgrove.

The show will be more whimsical than usual this year, and will include a range of unusual attractions including a “sex garden” sponsored by a company that sells vibrators. Visitors may get hot under the collar when touring the Aphrodite-themed “pleasure garden” full of flowers and plants associated with love and sex.

The RHS is asking celebrities to decorate gnomes to feature in the king’s garden, and they will all be up for auction. Those who have signed up include the actor Cate Blanchett and the cook Mary Berry. The RHS has lifted the gnome ban once before, in 2013 to celebrate the centenary of the event.