The seed quest: Tim Marshall's South American plant-hunting expedition could change the face of your garden

"Bring plants from some of the world's rarest habitats into your garden," the advert proclaimed, "and let someone else do the travelling." In true 19th-century style, the little ad in Euphorbia World magazine offered the opportunity to invest in a plant-hunting expedition to South America, in return for a share of seeds from new plants collected. If only I'd been in my club at the time, sipping port and reading a paper while the fire crackled.

In fact, what I did was to immediately reach for my computer and go to the expedition's web page, www.scampston.co.uk. "Become a £25 subscriber to the expedition, and you'll receive 10 packets of seed with field notes and cultivation tips," the expedition co-ordinator Anne told me. "And you'll be able to see photos on the website of your plants growing in their native habitat."

Anne will be co-ordinating the expedition's back-up, but it is Tim Marshall who is the intrepid explorer. Plant-hunting has changed dramatically in the past 15 years, as the long contracts on profit-sharing drawn up by teams of lawyers bear witness. Marshall's answer is to collect only seeds, which is a much simpler process legally. "I'm going to Bolivia and Chile and will be collecting only seeds permitted under international treaties," he explains.

Marshall spends most of his year overseeing the celebrated Scampston Walled Garden in North Yorkshire, which scores a hard-to-come-by two stars in The Good Gardens Guide. Garden writers can get awfully excited when talking about Scampston, throwing out phrases such as "a historic garden of the future". First worked on by Charles Bridgeman, the darling landscape architect of the Queen Anne period, it was then given a good going-over by Capability Brown.

The reason for the current interest is that the present Sir and Lady Legard, the owners of Scampston Hall, have tried to continue family tradition while looking to the future, so in 1998 they commissioned the Dutch founder of "new wave planting" Piet Oudolf to rejuvenate their ancient walled garden in his "prairie" style.

"I started working at Scampston as a placement on my horticultural course," Marshall says. "When I started to train, I wanted to grow succulents for a living, but working here changed my mind." In his private time, Marshall has retained his verging-on-obsessive interest in cacti and succulents, which developed when he was a boy: "I was 10, and I'd joined the British Cactus and Succulent Society. This chap, Brian Bates, gave a talk with slides about plant-collecting in Bolivia. It inspired me, and I said, 'When I'm old enough, I want to come with you.'"

For 13 years, Marshall has been making annual journeys to South America to collect seeds for Scampston's plant collections, and this year he's particularly seeking plants that we could grow in our gardens – he plans to stay at high altitudes to ensure what he collects has a chance in the British climate: his wish list includes fuchsias, salvias, begonias, passion flowers and my favourite, euphorbias. "We'll just have to see what's there," he says. "There's an amazing range of climatic zones in Bolivia; it only takes a day to get from the Andes to the Amazon."

It's not a money-making exercise – though Scampston hopes you will visit when the garden re-opens on 22 March. It's more about getting a share of the excitement and feeling the thrill of the traveller, without ever having to take off your slippers.

Seed shares are still available; see the website for details or call 01944 759 111

Read Emma Townshend's new column at http://blogs.independent.co.uk/independent/a_nice_green_leaf/