Forest gardens: Trunk call

They are the latest horticultural must-haves. But how to get one? <b>Anna Pavord</b> drops in on an expert

The forest garden is an attractive prospect, an edible landscape where the gardener can roam, collecting spiritual refreshment along with dinner. Those two strands were equally important to Robert Hart, whose smallholding at Wenlock Edge in Shropshire became a place of pilgrimage for his disciples. His book Forest Gardening (1996), written four years before he died, explored different and more holistic methods of producing crops. Why labour at digging the earth, planting fresh seed each year, when you could copy nature's way of providing a harvest?

Working in his own orchard, Hart developed a forest-garden model built up from seven different layers of planting. At the top is the canopy provided by mature fruit trees and under that a lower layer of smaller fruit and nut trees. Shrubs such as currants make up a third layer, with a herbaceous layer of perennial vegetables under that. Any remaining bare earth is covered with horizontal mats of herbs, or sprawling crops such as cranberry (if the soil is sufficiently acid). Hart built into his system an underground dimension of edible tubers and rhizomes and a final flurry of vines and other climbers that could pull their way up into the trees. It's the kind of mix you find in many English woodlands, though the plants there will not necessarily be edible.

Now, if you want to learn about the forest garden, your pilgrimage will take you west, to Martin Crawford and the Agroforestry Research Trust, based in a two-acre plot at Dartington in Devon. In fact, Crawford has plots scattered in several places round here, because he can scarcely keep up with demand for the plants he grows and the courses he runs each year. What is the draw, I asked, as we cowered in a polytunnel, waiting for the worst of the rain to pass. "A bit of it is the back-to-nature stuff," he replied. "And a lot of people now lead very busy lives. They think of the forest garden as a low input system."

Which it is. But only up to a point. "There's no such thing as a do-nothing garden," says Crawford robustly. "You can't just plant up a forest garden and walk away." Shelter is critically important, particularly if you aim to grow the more unusual plants that for some devotees is the whole point of the forest garden: blue honeysuckle, Szechuan pepper, tuberous nasturtium, plum yew. Most new converts want to get straight on with planting their crops. But, says Crawford, the shelter belt must come first.

Hart made his forest garden within an already established orchard. Crawford thinks it's simpler to begin with open ground, as he did at Dartington where he took over a piece of unused pasture. Getting the trees in is the easy bit, he says. It's the underlayers that need some thought. He used thick plastic sheets (Terram) to kill off the grass between the trees, gradually planting up one area at a time. Shade lovers will be more at home than plants that need sun. In Crawford's plot, apple mint romps away very successfully in what Hart might have called the fifth dimension, with Solomon's seal spearing up between.

I've never eaten Solomon's seal, but Crawford says the young shoots are excellent, gathered and cooked like asparagus. I've never eaten lime leaves either, but Crawford coppices his limes hard to get plenty of young growth and uses the leaves in salads. It's one of his best crops, he says, though it'd be a brave greengrocer who tried to sell them. Raspberries are a great success, because they can wander where they want, rather than being constrained to grow in the strip of ground to which we gardeners usually confine them. Crawford's canes were enormous. And his Solomon's seal hadn't been stripped by caterpillars, as mine always are.

Diversity, said Crawford. That's the secret. He reckons he's got at least 500 different kinds of plant growing in his Dartington plot. And because one plant muddles into the next in an amiable way, it's not so obvious which is what to a pest such as the Solomon's seal sawfly (Phymatocera aterrima). But if self-sufficiency is your aim, you'd be hard-pressed, even with these 500 plants, to feed yourself adequately. Hart was a vegan and lived mostly on raw food. But on a cold winter's evening, I'd be looking for something a little more comforting.

And a forest garden can't provide much carbohydrate, apart from sweet chestnuts which make a superb flour. I always buy it when we go to see my brother in France as, over here, it's absurdly expensive (£6.99 for 500g). Crawford mills his own which he gathers from the trees he planted when he first took on this plot, 20 years ago. This year there's a heavy crop and the squirrels leave them alone because they don't like the prickles.

Hart saw the sustainable forest garden as the ideal way to transform city wastelands, reconnecting the urban with the natural. Would I plant a forest garden, if I were starting afresh in our plot? No, but that's chiefly because I live surrounded by the spiritual refreshment of the real thing. There are hazelnuts in every hedgerow. Sweet chestnuts, too. Sloes and bullaces are abundant; so are elders and nettles and we use them all. This year, there's been an astonishing crop of parasol mushrooms in the fields around. And the irony is that, while people queue up to learn about the forest garden, I've not seen a single person out brambling, though luscious blackberries are bursting out all over.

Agroforestry Research Trust, 46 Hunters Moon, Dartington, Totnes, Devon TQ9 6JT. Send 4 x 1st class stamps (or visit agroforestry.co.uk) for a copy of Martin Crawford's excellent catalogue of fruit and nut trees as well as unusual vegetables and spices. Weekend (non-residential) courses in forest gardening cost £160. 2012 dates will be announced on the website. Meanwhile you can subscribe to 'Agroforestry News' for £21 a year (4 issues). Look out for Martin Crawford's book 'Unusual Vegetables', to be published next spring by Green Books (£14.95)

Five fabulous plants for a forest garden

Szechuan pepper (Zanthoxylum schinifolium) An intensely aromatic small tree or large shrub growing to 3m (10ft) with bunches of small, hard, red fruit that provide the pepper. The leaves can be used as flavouring. Hardy to -20C. £8.

Mashua (Tropaeolum tuberosum) A scrambling plant with very pretty, slightly glaucous leaves, peppery in taste like the garden nasturtium. Grown for its tubers, a staple in the Andes, unstarchy but nutritious. Two tubers for £4.

Turkish rocket (Bunias orientalis) A deep-rooted perennial brassica that comes into growth early in the year. Cook young new leaves like cabbage and the flowerheads – they come later – like broccoli. They have a mustardy flavour. £6.

Umbrella pine (Pinus pinea) All pines produce pine nuts but some are easier to get at than others. This is the best species to plant for nuts, eventually growing to 15m (50ft). £12.

Chinese mountain yam (Dioscorea batatas) The Crawford children's favourite vegetable, the yams produced like little potatoes all the way up a twining stem that can get to 3-4m. They do best in fertile soil. £5.