Tips on how to grow wasabi, cocktail kiwis and other exotic ingredients used by top restaurants in our own back gardens - plus, find out what else needs doing in the garden this week.

By Hannah Stephenson

Urban gardener and TV presenter James Wong doesn't have a greenhouse, propagators or teams of gardeners, yet through obsessive trials in his own back garden he has managed to grow a range of exotic fruit and veg worthy of any Michelin-starred restaurant.

He laments that we've become stuck in a 1940s timewarp during the 'grow your own' revolution, barely moving beyond spuds, sprouts and swedes.

"We don't eat the same stuff we did two generations ago, so why on earth should we be stuck growing it?" asks the Kew-trained botanist, who has fronted such TV programmes as the BBC's Grow Your Own Drugs and Countryfile.

"Ironically, the biggest mistake people make is trying to grow exotic crops in greenhouses when they simply don't need to."

Wasabi, also known as Japanese horseradish, which is used as a fiery accompaniment to popular dishes including sushi, is easier to grow than watercress, he insists.

Wasabi plants can't stand the sunshine, but thrive in cool, wet, overcast settings, which makes them perfect for growing in this country.

"They like semi aquatic settings, on the banks of bogs or shady forest areas," says Wong.

Plant out half a dozen small plants in a shady spot between early spring and early autumn, covering the area in a thick mulch of organic matter and place gravel around the plants to deter slugs and snails. Keep it in the shade in summer as they hate a lot of sun.

The edible part of wasabi is its partially buried stem, which takes up to two years to reach full size and flavour, but once you have an established clump, you'll have a succession of 'roots' for many years.

Harvest them when they reach around 10-15cm long - a third of this may be below ground - and grate them fresh at the table, because they will degrade within a few hours of being grated.

Wasabi works well in salad dressing and marinades for grilled chicken or fish, or whisked into mayonnaise. Currently plants are only available in a handful of mail order nurseries, but from next spring, Suttons will be supplying them.

Wong has also managed to grow cocktail kiwi, a pint-sized, fuzz-free version of the original, which he says is easier to grow than apples and pears, along with asparagus peas, dahlia yams and callaloo, a Caribbean 'spinach, on his urban plot. All are detailed in his latest book, James Wong's Homegrown Revolution.

The Inca berry, or cape gooseberry, imported from Colombia to supply the fancy fruit sections of certain supermarkets, was commonly grown in this country in Victorian times, says Wong.

"The plants can be grown like tomatoes but are not susceptible to blight, are more drought tolerant and you don't need to prune or train them."

Plant them against a sunny, south-facing wall in well-drained soil and cover their roots with a thick layer of mulch.

In late summer and early autumn the plants will produce a heavy crop of brown papery lanterns which fall off when they are ripe. The shiny golden berries within taste good as they are or as an interesting ingredient in smoothies, salads and salsas and have up to a three-month shelf life. The seeds are widely available.

Among Wong's favourites 'exotics' is the New Zealand yam, originally from Peru, which makes a much more interesting alternative to the potato.

Producing edible shamrock-like leaves with a flavour of Bramley apples followed by knobbly 'potatoes' in a variety of colours, they are also blight resistant.

"You cook and eat them in exactly the same way as potatoes, or you can eat them raw as a crudite In Mexico they dip them in sugar and chilli powder, which sounds awful but is really delicious," he enthuses.

Forming 30cm-high mounds, they make excellent ground cover under tall skinny crops such as sweetcorn or outdoor vine tomatoes.

They are grown like a regular spud, started off from seed tubers, increasingly available from specialist mail-order nurseries and from Thompson & Morgan. Plant them in small pots of compost on a sunny windowsill in late April.

They should soon spring up little shoots and will be ready to plant out in May after risk of frost has passed. They do best in rich, fertile soil packed with organic matter in full sun.

From July, earth up the rows to bury the trailing runners. They should be ready to harvest when the first frosts blacken their leaves in late November. Lift the tubers out of the ground carefully and hold a few back for planting in spring.

Even the world's most expensive spice, saffron, can be grown easily at home. Derived from a particular crocus, C. sativus, which has three distinct saffron threads in each flower, it was grown for more than 500 years in Saffron Walden in Essex, before Spanish imports became cheaper.

Corms, which are widely available, should be planted in late summer in free-draining soil in a sunny site and watered in well. Blooms should appear in as little as eight weeks and to harvest the saffron, pick the long red saffron threads out of the centre of each flower with a pair of tweezers, put them between two pieces of kitchen roll and dry them out on a hot radiator before transferring them to an airtight jar.

:: James Wong's Homegrown Revolution is published by Weidenfeld & Nicolson, priced £20. Available now.

Best of the bunch - Pennisetum (Fountain grass)

Fountain, or foxtail, grasses are among the most beautiful of deciduous ornamental glasses, their delicate-looking stems topped with long, narrow flowerheads in shades ranging from pinkish-brown to almost white.

The flowerheads are beautiful in their own right, particularly if grown in full sun when they look pink-tinged, and there are varieties which look lovely in beds and borders or in containers.

Try the dwarf variety P. alopecuroides 'Hameln' in containers or at the front of borders, as their compact flowerheads contrast well against other grasses with more diffuse flowers.

Other good varieties include P. orientale, which produces long, narrow, pinkish-white flowerheads, and P. setaceum 'Purpureum', an all-purple variety which can be treated as an annual or shortlived perennial. Pennisetums prefer full sun in light, well-drained soil.

Good enough to eat - Fruit tree preparation

If you've ordered bare-root trees from a specialist nursery, you'll need to prepare the ground now, choosing a mild, dry day to do it.

Dig over the whole area, adding plenty of organic matter such as compost or well-rotted manure to the soil. If you're only planting one or two trees, dig generous holes for each individual, which will accommodate the roots without cramming them in.

Loosen the subsoil at the bottom of the hole, then put plenty of compost in and work it into the bottom. It might be worth your while buying low stakes and tree ties now so that you have them to hand when planting.

If you haven't yet ordered your tree, take note of the rootstock - the top section of the tree which bears the fruit has been grafted at a very early stage on to the root of a different tree.

The chosen rootstock will affect the eventual size of your tree and the age at which it bears fruit. Good catalogues should give you plenty of information about the rootstocks they use and how big the trees will grow.

Three ways to... Control disease

1. Clean your knife when taking cuttings by wiping it with methylated spirit to prevent virus and other diseases being spread between plants.

2. Don't spray with fungicide in the evening when plants will be wet overnight - spray early in the morning on a dry day.

3. Pick off yellow, brown or damaged leaves and dead flowers to prevent fungal infection taking hold.

What to do this week

:: Take cuttings of roses and root them outdoors in a sheltered spot.

:: Fork over and clean up ground vacated by harvested vegetables.

:: Move evergreens and conifers growing in the wrong place.

:: Sow sweet peas outdoors in a sheltered spot.

:: Continue to harvest and store apples and pears.

:: Cut out blackberry canes when they have finished cropping and tie in new ones.

:: Continue to plant spring-flowering bulbs.

:: Make new lawns by sowing seed or laying turf.

:: Sow lettuces, spinach and turnips and plant out spring cabbages.

:: In the greenhouse, sow annuals in pots for a spring greenhouse display.

:: Dig up and store potatoes, carrots and beetroot.