What to Eat: Food that’s good for your health, pocket and plate. Joanna Blythman

To obtain a good emulsion, combine the vinegar with a little smooth mustard, sea salt and pepper before whisking in the oil. If you like a sweeter taste, add a drop of honey to the mustard and vinegar mix.

      • Sweat watercress in butter with some onion and potato and/or peas, add stock and liquidize to make a verdant, punchy, easy soup.

      • Braise halved Little Gem or baby Cos lettuce in butter and chicken stock until soft and juicy, adding a little cream to finish off.

      • Heads of chicory or crunchy lettuce hearts, either blanched or steamed, make an unusual winter gratin when wrapped in thin slices of ham and baked in a béchamel sauce.

      Are lettuce and salad leaves good for me?

      Leafy salads are sometimes dismissed as being mainly water, which is true up to a point, but also misleading since they also provide valuable levels of antioxidant vitamins, minerals and trace elements that we particularly benefit from because we eat them raw. Lettuce has also figured in traditional medicine for centuries as a sleep-promoting food.

      Levels of micronutrients vary from one type of salad leaf to another. Cos lettuce, for instance, is packed with vitamin C. Watercress stands out as a nutritional treasure trove. It is loaded with vitamins C and E, and beta-carotene which help neutralize the damage done by harmful free radicals that can predispose the body to disease; folate, which helps prevent birth defects; and zinc, which supports the immune system. All salad leaves contain these, but at lower levels. Watercress has a time-honoured place in traditional medicine as a tonic, purifying food and as a remedy for skin problems.

      The nutritional value of salad leaves starts to diminish as soon as they are picked so it is important to eat them as fresh as possible. Research suggests that bagged salads sold in puffy ‘pillow’ packs filled with modified atmosphere have fewer vitamins and folate than the freshly cut equivalent. This could be because although the modified atmosphere keeps the leaves looking fresh and green beyond their natural shelf-life, some nutrients are depleted by the storage process. This deterioration is likely to be even more rapid in bags that contain leaves that have been torn and cut.

      Bags of salad leaves that are sold as ready-to-eat will have been washed in water. Unless they are organic, this water usually contains chlorine, an oxidizing disinfectant, which may also reduce their micronutrients. Some retailers now have their salad leaves washed in spring or ozonated water instead to improve the taste and reduce the chance of chlorine by-products lingering on the leaves. But unless your salad bag label says otherwise, assume that chlorinated water has been used. It is always a good idea to wash bagged salad leaves even if they are ready-to-eat as an extra precaution, both against food poisoning bugs that might have colonized the packs during processing, and to rinse off any lingering chlorinated water.

      Due to their open leafy shape, lettuces and salad leaves are particularly likely to trap pesticides. Since the early 1990s government testing of UK-grown salad leaves has revealed an ongoing problem with pesticide residues, so much so that the government now checks them on a regular basis. This residue problem has been most evident in lettuces, both UK-grown and imported, that have been cultivated in glasshouses and in polytunnels, rather than the open field, because they get particularly heavy fungicide treatments. The protected environment creates the perfect climate for the development of rot and the carry-over of disease from one crop to the next.

      Follow-up action taken by the authorities against growers producing lettuces with unacceptable levels of pesticides has reduced the incidence of residues somewhat, but lettuces are still routinely found that have multiple residues of various pesticides. Illegal use of pesticides not approved for use in the UK is often also detected. If you want to reduce your exposure to pesticide residues, there is a strong case to be made for buying organic salad leaves. Hardly any pesticides are approved for use in organic growing and no pesticide residues have been found in recent years in organic salad leaves.

      How are lettuces and salad leaves grown?

      Lettuces and salad leaves were traditionally grown outdoors in open fields, but nowadays many of the lettuces and leaves we eat, whether home-grown or imported, are cultivated in polytunnels or glasshouses. Growing salad leaves under some sort of cover allows growers to extend the growing season because it keeps the crops warmer and protects them from weather damage. In recent years there has been a technological revolution in growing some salads under cover in a temperature-controlled environment using soil substitutes (see PEPPERS/How are peppers grown?).

      British watercress is grown in a different way to other salad leaves. Traditionally foraged from streams, these days it is cultivated in shallow, gravel-lined concrete beds in a gentle flow of water from natural springs and underground bore-holes. In the UK, the key watercress-growing areas are Hampshire, Dorset and Wiltshire. As the cress grows in water, it doesn’t freeze in winter as tender, soil-grown green leaves would do. This means that although watercress used to be considered a late spring and summer crop, we now have year-round watercress production.

      Are lettuces and salad leaves green choices?

      From an environmental perspective, it makes no sense to eat lettuces and salad leaves that have been imported from abroad. These have to be trucked long distances in refrigerated vehicles, which uses up a depleting resource – oil – and contributes to climate change in the form of vehicle emissions. As a wide variety of lettuces and salad leaves can be grown in the UK for the best part of the year, there is no need for environmentally destructive imports. Watercress is a ‘green’ choice in more than one respect: watercress beds provide a particularly attractive natural environment for kingfishers, warblers and other rare birds and encourage otters to set up home in nearby rivers. In wintertime, when the availability of UK-grown leaves and lettuces is more limited, a more environmentally aware approach is to ring the changes with native seasonal vegetables.

      Where and when should I buy lettuces and salad leaves?

      Salad leaves used to be thought of as a summertime food. Now we tend to think of them as something we can eat year round. If you want to eat UK-grown salad leaves and lettuces, then the selection will change throughout the year and be smaller, but still worthwhile, in the winter. When buying salad leaves, use your common sense and think seasonally. As a rule of thumb, the more bitter-tasting leaves such as chicory will continue to grow in Britain in winter and many other types, such as landcress, watercress and lamb’s lettuce, make excellent winter salads. More tender leaves and lettuces don’t naturally thrive outdoors in the UK except from early summer until autumn. Supermarkets offer a year-round availability of salad leaves and lettuces. In the winter months they will be imported, usually grown in glasshouses and polytunnels in North Africa and southern Europe.

      If you feel daunted or bored at the thought of getting through a whole head of lettuce, check out the fresh mixed leaves selections on farmers’ markets stalls, from box schemes, farm shops and natural food stores which usually offer a more interesting array than the supermarket equivalent. Another way to transform your supply is to grow your own ‘cut-and-come-again’ salad mix, sometimes called ‘misticanza’ or ‘saladini’ in a container (on a patio, balcony or windowsill) or in the garden. Even the smallest space will give you a varied summertime crop that you can snip away at, enlivening other more humdrum lettuces and leaves.

      Will lettuces and salad leaves break the bank?

      Weight for weight, it is much cheaper to buy a whole lettuce and wash it yourself rather than just stumping up for a bag of salad leaves. At a glance, the contents of these bags might look quite adventurous, but on closer inspection, you will probably find that they are padded out with cheaper substitutes – red cabbage instead of radicchio, for instance – which makes them unexciting and poor value for money. There is no point in paying more for ready-washed salad leaves because it is best to wash them yourself at home as a health precaution.

      If you think you can’t get through a whole lettuce at a time, simply strip off a few leaves and return the heart to the salad compartment of the fridge. If you want to use a mix of leaves, but can’t see how you can use them all at once, you can wash them all together, take what you want for that meal, then keep the rest inside a plastic salad spinner with a lid on in the fridge where, if truly fresh to start with, they should keep for a couple of