Strange fruit: The secrets of the River Cottage garden

As head gardener at River Cottage HQ, Mark Diacono grows all kinds of things you can eat. But it's in his own backyard that he really branches out, as Anna Pavord discovers.

(George Wright)

"There are no mistakes," says Mark Diacono boldly, "just experiences you probably shouldn't repeat." If you are a River Cottage fan, you'll already know all about Diacono, head gardener at Hugh Fearlessly Eats-it-all's HQ near Axminster, Devon. But a little further west, Diacono has his own HQ – 17 acres of smallholding that he bought on a whim five years ago.

There, he's been whipping quite fast through experiences he probably shouldn't repeat to emerge, triumphantly, with his land covered in plantations of strange crops: Sichuan pepper, blue honeysuckle (for the fruit), pecans, Egyptian walking onion and goji berries. He's planted swathes of walnuts and chestnuts, quinces and medlars. But he's also watched his apricots die of canker and his olive trees, 120 of them, shiver to a standstill in the -14C winter that we've just been through. Olives aren't generally expected to cope with temperatures below -10C.

"I just got the wrong olives," says Diacono, who views these disasters with a cheerfulness I don't think I could ever muster. Physically, it's fantastically hard work planting orchards in untilled ground. But already, he's acquired a hundred new baby olive trees (the right kind) that are flowering their heads off in pots in his polytunnels. Some time soon, he'll be planting a new olive orchard, pinning his faith on the Catalan strain that is apparently behind all the new commercial plantings going on in Argentina and California.

"I'll set them out next year," he says. "I'll grow them like vines. Much closer together. Like a hedge. They'll work like that much better. I'm really excited about my new olives." And that is what makes Diacono so engaging. He doesn't moan on about how much he's lost on the first doomed olive venture. He doesn't give up after this initial, quite major setback. He doesn't think that there's a good reason why the UK is not full of the silvery gleam of olive leaves. As far as he's concerned, the wheel can be reinvented.

And he does love a project. He recognises this as a trait in his personality which sits, not always comfortably, alongside another aspect – a tendency to sit down and do nothing. "There's not much in the middle," he says disarmingly. He did nothing for quite a long while after he arrived with his wife, Candida, at the smallholding. The epiphany came in the bath, reading Jane Grigson's fruit book. "Mulberries," he thought.

In fact it turned out not to be mulberries that he planted first, but walnuts and sweet chestnuts. Only after he'd planted out 30 of each did he realise that he'd used up most of his ground on trees that took up a lot of room and would take years to crop. So he dug them all up, set them out in the hedges round his land and waited for another brainwave. "You see," he says, by way of explanation, "when I took this place on, I genuinely had no idea what I wanted to do with it. I got it because although life was OK, it was a bit aimless. And when I finally got the land, I realised I would never want to grow a crop just because it would be good business. I've got to love it."

He's a quick learner though, and the success last year of his River Cottage Handbook: Veg Patch (Bloomsbury £14.99) led quickly on to a new idea – a book about things he loves to eat, but which are still strangers to most of our gardens: Chilean guava, kai-lan, oca, yacon, Carolina allspice. They are all there out on his smallholding, many of them growing either in the patch he calls his perennial allotment, or in what will one day be a forest garden.

Both ideas depend on the same notion – that ground does not have to be turned over and replanted each year. Food crops once put in, stay in. The gardener becomes a kind of referee, occasionally wading in to restrain alpine strawberries or lift the canopy of a tree. The idea is to replicate, with more complicated ingredients, what nature does for herself in any hedgerow in the West Country, providing hazelnuts, hips for jelly, blackberries, elderflower for cordial, hops for beer, sloes for gin. If plants like the same growing conditions, they can share the same space.

Diacono is very keen on the idea of the self-sustaining perennial allotment. Don't waste space on potatoes and onions that you can buy easily and cheaply, is the message. Grow stuff you can't buy, that will add a buzz to your cooking. So the perennial allotment is planted with oca (a tender kind of oxalis that produces a tuber tasting like a salad potato), edible honeysuckle and fuchsia. Like rabbits on a spree, we nibbled on tree spinach and musk strawberry, day lily flowers (the yellow kinds are the sweetest) and vegetable oyster (Mertensia maritima), a glaucous-leaved plant with blue flowers.

Diacono is 43 and impatient now for the various bits of puzzle he's put on his smallholding to make a full picture. "I'm new to gardening and late to it. If I'd started at 20, I'd have planted windbreaks before I did the rest of the stuff." I bet he wouldn't, though. Tedious things windbreaks. And orchards of Sichuan pepper (Zanthoxylum schinifolium), which grow not from a vine like black pepper but on a shrubby kind of bush. It's a staple of Chinese cooking and Diacono reckons that once his 200 bushes start cropping in earnest, restaurants will snap up everything he's got.

So the future is rosy with dreams of pepper harvests. And of organic wine. The latest wheeze is several acres of vineyard, planted half with disease-resistant Seyval Blanc, and half with a mixture of Pinot Noir, Gewurztraminer and Sauvignon Blanc. In his mind's eye, he can already see 20,000 bottles of English wine lined up in a cellar. For smallholding, read terroir. Unreservedly, I admire his energy. And his optimism.

Mark Diacono's new book 'A Taste of the Unexpected' (Quadrille £20) will be published in September. For more information about making a forest garden, go to edibleforestgardens.com, or contact the Agroforestry Research Trust at agroforestry.co.uk. To buy a wide range of unusual edible plants (including yacon and oca) go to Edulis at edulis.co.uk