Friends in high places: How New York's High Line founders raised $100m

How to get $100m, that's the question. People claiming to be top Nigerian businessmen take one well-known route. There's also, of course, Euromillions. You never know your luck. Or finally, like Joshua David and Robert Hammond – who quite fancied building a completely new public park in the centre of some of the most expensive real estate on the planet – you could just, um, start asking.

Yep. Ask. Bizarre. And now, factor in that New York City neighbours David and Hammond didn't even know each other. They met for the first time at a community planning meeting in 1999 about whether to demolish the long-abandoned High Line, an elevated railway which ran through their Chelsea neighbourhood. Rising 30ft above the ground, the railroad closed in 1980, leaving, basically, an elevated mess.

The High Line had delivered freight, from Animal Crackers to cigars to a final farewell load of turkeys, but it was something more elegant that David and Hammond had in mind when they came up with the frankly bonkers idea of putting a park on top of it. Of course, the French had done it first. Promenade Plantée in Paris makes its way along an abandoned viaduct on the old Vincennes railway line in the 12th arrondissement: roses and hydrangeas feature heavily, among formal ironwork columns. But in Manhattan, the High Line had already grown wild in the 20 years since trains last ran on its tracks: Virginia creeper, smoke bush, black cherry and Queen Anne's Lace. From the start, the Friends of the High Line decided that the wildness should stay.

A little more than a decade on, you can see the results for yourself: On the High Line, Exploring New York's Most Original Urban Park, by Annik La Farge (Thames & Hudson, £19.95) is packed with photos expressing exactly how much High Line Park has contributed to city life. Pretty girls dozing, bendy people doing yoga, kids splashing in water, grown-ups making full use of the built-in sun loungers: here are the citizens of the city, making the most of a brand-new public space. The first section opened in 2009, the second in 2011, and the third is still in planning – awaiting a little bit more of High Line's fundraising genius.

While we wait, the book captures exactly the delightful design and planting. New York landscapers Diller Scofidio + Renfro and internationally celebrated plantsman Piet Oudolf put together a plan which means no two sections are alike, and if you keep walking, you keep seeing new things: a field of wild carrot with the shores of New Jersey in view; a stretch of grassy lawn overlooking 23rd Street. New York City's watertowers and warehouses, its hotels and billboards, its bridges and its fire escapes: they're all visible, at odd angles you'd never expect. The book captures the spirit of each little section of the park – the whole thing a mile-and-a-half long but just 40ft wide. It has the gentle reader reaching for the internet to start looking for plane tickets.

But as for how they got together that huge pile of funding: buy a ticket for the autumn seminar on the High Line at the Garden Museum, London SE1, where the afternoon session on 5 October should hold the answers. Both the High Line's founders will be there, as will current chief Melissa Fisher, to explain how they wheedle huge donations out of corporate donors (from Tiffany to Diane von Furstenberg), run a massive "friends" programme and chivvy cash from nearby property developments. Its title? "How to raise $100m".

The High Line Symposium runs over three days and will also include a session by Piet Oudolf, who designed the planting. See gardenmuseum.org.uk for details

High Line planting: Piet Oudolf favourites

Achillea 'Cloth of Gold'

Bright yellow platters planted among prairie grasses with seed heads standing till winter. £5.99

Eryngium yuccifolium

A huge sea holly, growing to almost 2m high with fantastic white foliage and structural leaves. £7.99

Echinacea 'Elton Knight'

A key Oudolf element, this one flowers late in September to spectacular effect. £9.99.

All plants from crocus.co.uk