A very large bronze tree has sprouted in Waverley Station. Created for the Edinburgh Art Festival, which opens this weekend, it is called Tree No 5, is made from bronze and acrylic, and is only the first yield from what would could be a fantastical garden to be created by Scottish artist Charles Avery.

Avery’s work, five metres high, is one of seven commissions at this year’s EAF, which is now, its director Sorcha Carey says, the biggest visual arts festival in the UK. The tree is the first solid vegetation from a larger ongoing project, The Islanders, which Avery – who was born in Oban in 1973 but grew up on Mull – has been working on, with drawings, sculptures, installations, texts, paintings and moving images, since 2004.

This fictional Island takes another step from the fantastical to the real with the tree, which the artist says is both an experiment in form and the precursor to something larger – the garden of Jadindagadendar – and also, more practically, an architectural addition to Edinburgh's famous old train station. It also serves as a towering addition to his larger show at the nearby Ingleby Gallery: The People And Things Of Onomatopoeia.

“I was installing an exhibition in Paris in 2010, eating a sandwich in a beautiful garden nearby, and I thought 'I want to make a municipal park for the Island',” says the artist, who is now London-based. “I thought it should be called Jardin or Garden, I was messing around with the words, so I hit upon the word Jadindagadendar. I was thinking about how the Islanders think about nature, and they kind of refute nature really, so they have created this mathematical garden – rather like how a Cargo Cult would look at trees. They would see what their characteristics were and try and imitate them. This is just one specimen from what I hope to achieve, which is a whole garden.”

Where would that garden be, I wonder?

“I think it would be modular, so it could grow to occupy different sizes of space. Trees could be telescopic elements, but there would be a central eponymous tree, the massive Jadindagadendar tree, which would have boughs to extend to all corners of the garden. That would be illuminated. It would be the tree or life or knowledge. I can imagine that garden being a place where you could perform monologues or single-act plays, maybe on a philosophical nature. It could be the Socratic dialogues or George Bernard Shaw’s Back To Methuselah [from 1922] so I can imagine it being a stage or a forum for other people’s activities.”

Avery says that that stage or forum is how he views his whole The Islanders project. “It is place where other people can embed their own ideas, where they can have their own reasoning of political or philosophical issues.”

The tree itself will be in place at Platform 2 of the station for the duration of the festival, and then it will be shown at the Parasol Unit in London.

“I want it to be quite light, I am not pushing it as art,” Avery insists. “On the Island it would be something that might happen in little circuses in the town. People might sit and have their sandwiches there, tie their shoelaces, a dog might lift his leg on it. I don’t want it to be in-your-face – I want it to be more architectural. But who knows? It’s an experiment.”

And The Island itself? When will Avery be able to leave his own creation? He says that ideally he can condense the information into a series of books or encyclopaedias.

“There will be a time when it reaches critical mass,” he says. “For the first ten years I have been working out how to do it, what is important and what is not important. You can never finish it, but you can stop doing it.”

The Edinburgh Art Festival spans 40 exhibitions across 30 galleries, museums and spaces from July 30 to August 30, www.edinburghartfestival.com