The weed that works wonders

What's green, grows in water and fights cancer? If we had more sense, we'd be eating the answer, says John Hurd, Britain's pioneering grower of organic watercress. For 46 years he has harvested this much-neglected power- food from watercress beds at Hill Deverill in Wiltshire. What upsets him is how quickly people have forgotten the benefits of this wonder weed.

What's green, grows in water and fights cancer? If we had more sense, we'd be eating the answer, says John Hurd, Britain's pioneering grower of organic watercress. For 46 years he has harvested this much-neglected power- food from watercress beds at Hill Deverill in Wiltshire. What upsets him is how quickly people have forgotten the benefits of this wonder weed.

"Throughout the war," he says, "the traditional Sunday-night tea was watercress and vinegar, with a bit of bread and butter if you could get it. It was a treat. Now we've forgotten all that."

Hurd's forerunners once nourished the capital's workforce. In 1851, Henry Mayhew wrote admiringly of the Farringdon watercress market and the network of nearly a thousand street-sellers who were on their rounds "in time for the mechanics' breakfast". Today, alas, few mechanics, or anyone else, scoff handfuls of the peppery leaves with their morning tea.

Relegated to the status of garnish, John Hurd's traditional bunches are hidden among "pillow packets" stuffed with lettuce leaves on supermarket shelves.

Nutritionally, watercress is loaded with goodies. Just a 100g of watercress (three-and-a-half ounces) supplies an adult's entire daily vitamin C requirement, 52 per cent of vitamin A needs, and just 23 calories. The stuff is a dieter's dream. Weight-for-weight, watercress delivers more iron than spinach and more calcium than milk. Yet as a nation, our consumption of watercress is pathetic: something like per person, one 130g packet per year.

Watercress is not just nutritionally rich; it is medicinal. Stashed within those heart-shaped leaves and sturdy stems is an armoury of anti-cancer agents. By all accounts, it is the mustard oils - the compounds that give watercress its peppery taste - that are the active anti-carcinogens. In particular, one compound, called phenylethyl isothiocyanate, has been shown to ward off cancers in three different ways.

First, the compound inhibits so-called phase one enzymes, responsible for activating carcinogens within the body. Secondly, it activates phase two enzymes, which help the body to detoxify and excrete potential carcinogens. Finally, the magic mustard oil can even induce cancerous cells to commit suicide - a process known as apoptosis.

Last year, Stephen Hecht at the University of Minnesota Cancer Center showed that smokers who agreed to eat 50g of watercress a day soon began to show an enhanced ability to rid their bodies of tobacco carcinogens through their urine. Richard Mithen, Peter Rose and Kathy Faulkner of the John Innes Centre in Norwich, working with Gary Williamson at the nearby Institute of Food Research, have found at least three other mustard oils that also powerfully induce phase two enzymes, which boost the body's ability to eject potential toxins.

"Watercress turns out to be a mixture of compounds that act in different ways but are all rather good for us," says Mithen. The plant itself probably manufactures these mustard oils to deter herbivorous aquatic shrimps, snails and the like.

Watercress's powers may even extend beyond prevention. Researchers are investigating watercress's potential as a therapeutic agent, following suggestions that a diet rich in watercress may slow the development of prostate tumours.

If watercress is the perfect indicator of a healthy diet, it was once a sign of a healthy watercourse, too, thanks to the unique way in which it grows. Alone among our vegetables, it renounces soil. Only clear running water will do. Once people could pick watercress from fast-running streams where it grew of its own accord. In the 19th century it began to be cultivated in many parts of southern England, wherever clean streams were plentiful - in Dorset, Wiltshire, Hampshire, and even Surrey.

By the turn of the century, according to local historian John Legh, almost every village in the Chilterns had its own watercress beds. Today, no working beds remain, though the Chiltern Society is attempting to restore beds at Ewelme as a record of the once-ubiquitous industry. Sadly, though, no cress will be sold for human consumption from the restored beds. "Water shortages and a greater concern with the purity of the water supply have taken their toll," says Legh.

John Hurd is therefore a rare survivor. His five acres of watercress beds rely on a daily dose of almost three million gallons of high-quality mineral water drawn up from the underground aquifers north of the White Sheet Downs. Once through the cress bed, the water flows into the river Wylye, ready to meet the many demands downstream all the way to Salisbury.

Grow watercress organically, and no toxic pesticides and fertilisers end up downstream. Wildlife benefits in other ways, too. The now-rare native crayfish as well as the water shrew may find a hospitable corner in a peaceful bed, where the crop is harvested and replanted infrequently. A few decades ago, the beds were an important habitat for nesting redshanks and over-wintering water pipits. But such wildlife riches are a rarity now, in the wake of an explosion of intensively managed watercress beds, with up to 10 croppings a year heavily dependent on fertilisers and pesticides.

"Compared to other salads, there is little chemical input to watercress," says Dr Steve Rothwell of Vitacress, Britain's leading watercress producer and part-funders of the Norwich anti-cancer research. Because watercress uniquely grows in fast-running water, it has far fewer pests than lettuce. All the same, whatever you do add to watercress inevitably ends up in the river, if only in trace amounts. Non-organic growers may dose their crop with extra fertilisers as well as organophosphate pesticides, such as malathion and dimethoate. These pesticides are classified as "suspected" or "possible human carcinogens" by the US Environmental Protection Agency, says David Biffin of the Pesticide Trust in London, which is about to launch a new report on pesticides in water.

The Environment Agency has the difficult task of policing the "effluent", ensuring that pollutants and suspended solids released when the beds are cleaned are kept within agreed limits. "Sometimes the growers whinge," says Malcolm Munroe of the agency, "but they have money to make." Meanwhile, intensification continues. "They're turning up the screws, producing more and more cress on the same acreage." Something has to suffer, and traditionally it's been our rivers.

But organic growing in Britain is on the increase. Today more than 75 per cent of Britain's watercress is controlled by just two commercial growers, Vitacress and the Watercress Company, and both are now putting a toe into the organic market. Vitacress, for instance, has organic beds at Dorchester, as well as four acres at Spetisbury, on the Stour.

John Hurd's new competitors come equipped with winter farms in Portugal and Florida - farms which, organic as they may be, do nothing to improve the quality of Britain's waterways. Hurd's organic beds cannot produce enough in winter to satisfy supermarkets, but he can continue to supply local organic veg- box schemes. The subterranean water is warm enough to keep the crop green and growing even in December frosts. It can't grow quickly, nor produce a massive yield, but that's not necessarily a bad thing. The slower the cress grows, and the more mature it becomes before harvest, the richer it is in cancer-busting mustard oils.

Growing organically means growing slowly, with less pollution and more nutrition. "You don't get the yields," says Rothwell, "and the premium doesn't cover the lower production." But eat organic watercress, patiently grown, and you promote the health of both humans and rivers. The product is living proof that we can make careful use of our natural waterways without degrading them.