Hydroponic
Lettuce is a fairly hardy, cool-weather vegetable that thrives when the average daily temperature is between 60 and 70°F. It should be planted in early spring or late summer. At high temperatures, growth is stunted, the leaves may be bitter and the seedstalk forms and elongates rapidly. Some types and varieties of lettuce withstand heat better than others.

There are five distinct types of lettuce: leaf (also called loose-leaf lettuce), Cos or romaine, crisphead, butterhead and stem (also called asparagus lettuce).
Butterhead lettuce produces high-quality greens that mature slightly earlier than crisp-head varieties, but are less tolerant of warm weather. They include the Boston and Bibb types, characterized by undulating leaves with a soft buttery texture and a mild, sweet flavor.
Loose-leaf lettuce matures quickly and is easy to grow. Try heat-resistant varieties such as Oak Leaf or Salad Bowl for July and August harvest.
Pound for pound, the crisp, green leaves of Romaine lettuce are among the best nutrition bargains. Romaine, or cos, type of lettuce produces an elongated head of stiff, upright leaves ready about 60 days from planting.

Spinach adds a punch of color and nutrition to the salad. It grows best under cool temperatures and shorter days, so it should be planted very early in the spring and again in the fall as temperatures cool.

Endive is in the same family as lettuce, but with lots more flavor than many types of lettuce. Curly endive, sometimes called chicory, has curly-edged green leaves. Escarole, another relative of chicory, has broad, wavy green leaves with a pleasant slightly bitter flavor.

Lettuce leaves should be free of wilt, rot and rust. Harvest crisp green leaves. Wrap fresh, unwashed leaves in plastic wrap and store in the refrigerator for a few days if necessary. Cooler temperature will keep lettuce fresh longer. The coolest part of most refrigerators is usually on the first shelf against the rear wall.

Avoid storing lettuce with apples, pears or bananas. These fruits release ethylene gas, a natural ripening agent, that will cause the lettuce to develop brown spots and decay quickly. Toss lettuce that looks slimy or has black spots. The slime is the residue of bacterial decomposition and the black spots are usually mold.

Nutritional Value & Health Benefits The nutritional value of lettuce varies with the variety. Lettuce in general provides small amounts of dietary fiber, some carbohydrates, a little protein and a trace of fat. Its most important nutrients are vitamin A and potassium. The vitamin A comes from beta carotene, whose yellow-orange is hidden by green chlorophyll pigments. Beta carotene, of course, is converted to vitamin A in the human body. The darker green, the more beta carotene.

According to the American Cancer Institute and the American Cancer Society, foods rich in vitamin A and C (antioxidants) offer protection against some forms of cancer. Along with other phytochemical, antioxidants reduce the risk of cancer of the respiratory system and intestinal tract.

Lettuce, except iceberg, is also a moderately good source of vitamin C, calcium, iron and copper. The spine and ribs provide dietary fiber, while vitamins and minerals are concentrated in the delicate leaf portion.

 
Preparation & Serving Rinse lettuce just before serving in very cold water. Pat dry with a clean towel. Limp leaves can be revived by immersing in ice water for a few minutes. Tear lettuce leaves into pieces. If practical, do not cut or sliced lettuce leaves in advance. Damaged cut lettuce leaves release an ascorbic acid oxidase, which destroys vitamin C. Cut edges also discolor quickly.

Dry leaves before serving. Salad dressing will cling to dry lettuce leaves instead of sinking to the bottom of the salad bowl. Toss with your favorite dressing just before serving (or serve dressing on the side) Lettuce leaves covered with dressing will quickly wilt.