As people become more nutrition conscious, salads become an essential part of a healthy meal, or even as the meal itself. Part of the reason for the popularity of salads is the freshness of the principal ingredients. For years, iceberg lettuce dominated the choice of salad greens, but today other lettuces are also popular. Greens from other botanical families are becoming frequent additions to fresh salads, as well. If iceberg is the only type of lettuce you eat, you are choosing the least nutritious member of a family of nutritional champions. Any other lettuce or leafy green vegetable would be a better choice. Most other greens are also good sources of vitamin C, beta-carotene, folate, and dietary fibre as well as some calcium.

As a general rule, the darker green the leaves, the more nutritious the salad green. For example, romaine or watercress have seven to eight times as much beta-carotene, and two to four times the calcium, and twice the amount of potassium as iceberg lettuce. By varying the greens in your salads, you can enhance the nutritional content as well as vary the tastes and textures.

Salad greens must be fresh and crisp. It is easy to spot wilted greens; watch out for limp, withered leaves that have brown or yellow edges, or dark or slimy spots. Once greens have passed their prime, there is no way to restore them to crisp freshness. Lettuce and other greens should be displayed under refrigeration, as they are very perishable vegetables.

Try to choose lettuce with healthy outer leaves; these are likely to be the most nutritious part of the green, containing much more beta-carotene and vitamin C than the pale inner leaves. Unfortunately, the outer leaves are usually the most damaged part of the head, but from a nutritional standpoint, it's best to salvage as many as you can.

Iceberg and other head lettuces should be symmetrically shaped. Choose a head with its dark green outer leaves intact and healthy looking. The stem end of a head of iceberg lettuce may look brown; this discolouration is the natural result of harvesting and does not indicate damage. If the head is not wrapped, sniff the stem end: It should smell slightly sweet, not bitter.

Iceberg lettuce should be compact and firm, yet springy: Very hard heads may be overmature and bitter. Avoid overly large heads of romaine, which may have tough, fibrous leaves.

Most lettuces and other greens keep best in a plastic bag in the refrigerator salad drawer. Soft leaved lettuces do not keep as well as firm greens, such as romaine or iceberg lettuce: Iceberg should keep for up to two weeks, romaine for about 10 days, and butterhead and leaf lettuces for about four days. Buy only enough for immediate use, or keep them for more than a day or two.

Don't store greens near fruits, such as apples or bananas, which give off ethylene gas as they ripen. Otherwise, the greens will develop brown spots and decay rapidly. For appetisingly crisp greens, and to minimise last minute preparation at mealtime, wash and dry them, then layer the leaves in clean paper towels and place in a plastic bag. Refrigerate in the salad drawer until serving time, but not more than a few hours, for optimal nutrient retention.

If you purchase a cellophane wrapped head of iceberg lettuce, leave it in the wrapper until you are ready to use it. Untie bunches of greens, such as watercress, and check them for insects. Greens sold with their roots intact keep best if you wrap the roots in damp paper towels, then place the whole bunch in a plastic bag. Greens with their roots attached can also be placed upright in a glass of water (like a bouquet of flowers), covered with a plastic bag, and refrigerated.

Greens must be washed, and in some cases trimmed before you put them in the salad bowl.

Since grit tends to collect at the stem end of looser-headed greens, it's important to twist off the stem and separate the leaves before washing them. (If you're not using the entire lettuce at one meal, just remove as many leaves as you need from the stem.)

To wash small leaved greens on stems, cut off the roots, hold the greens by the stems, and swish them around in a large bowl of cool water. Lift out the leaves, letting the sand and grit settle, then empty and refill the bowl and repeat the process.

A salad spinner greatly simplifies the preparation of greens by drying them quickly and thoroughly. Dry leaves are a must if the dressing is to adhere properly.

It's best to core iceberg first: Cut the head in half lengthwise and then remove the core with a stainless steel knife; or, rap the head, core-end down, then twist and lift the core out. If you're using the whole head, rinse it by running cold water into the cored end, then invert the lettuce to drain it well.

You can either tear greens into bite-sized pieces by hand or cut them with a knife; each method has its proponents. As long as you use a stainless steel blade (carbon steel can cause blackening and alter the flavour) and serve the salad soon after it's prepared, it's safe to cut most greens. However, delicate leaves, such as butterhead lettuce , are more appealing when torn (or left whole). Iceberg lettuce can be cut into thick slices ("rafts"), wedges, chunks, or shreds, or simply torn.

In addition to their use in salad, many salad greens can be briefly cooked and served as main-dish or side-dish vegetables. The firmer and more strongly flavoured greens, such as escarole or chicory, benefit the most from cooking by mellowing the taste. Even butterhead lettuce can be braised.