Originally cultivated in the temperate parts of Kurdistan, Kashmir, and Siberia; the Romans grew a pointed, narrow-leafed Cos, like the Rabbit’s Ear lettuce we grow today.
The leaves are widely eaten raw, especially in tossed salads and sandwiches. Lettuce also is boiled as a potherb, pickled, braised, sauteed, fried, pureed, or used in soups and stews. Sprouted seeds can be used in salads and sandwiches.
Lettuce thrives under cool, moist conditions and can survive a light frost. Long, hot days generally prompt plants to bolt (send up a flowerstalk); the sap in the leaves turns unpalatably bitter, and the harvest ends. To reduce hot weather stress, water regularly, keep the ground cool by using an organic mulch, and provide partial shade. Lettuces welcome shade from taller crops. In return, Lettuce helps keep the weeds in check and the soil cool.
Soaking Lettuce seeds in a 10% bleach solution for a couple of hours can markedly improve their germination rates at high temperatures (30-35o C/85-95o F); follow with a thorough rinsing with distilled water. To sow Lettuce seeds directly, thoroughly moisten the soil and sow seeds in clusters spaced 20-30 cm (9-12 in) apart each way. A rich, loose soil with a pH between 6.0 and 7.0 is ideal. After germination, eliminate all but the strongest plant at each station.
Seed may be sown every two or three weeks at the end of the rainy season, through the cold season, and until the very beginning of hot season.
Harvesting and Seed Production
Lettuce is harvested any time after its true leaves form. Some gardeners cut entire plants to within 5 cm (2 in) of the soil (the plants produce more leaves in about a month); others harvest only the mature outer leaves.
Saving Lettuce seed is simple; if you leave Lettuce unattended; it will bolt, flower, and in a short time self-seed. The seed stalks of head Lettuce varieties can more easily push up through the heads if you slit or twist the top of the head. Lettuces are self-pollinating, but a very small amount of natural cross-pollination occurs-from one to six percent-when two varieties are grown side by side. A barrier crop between different varieties flowering at the same time should reduce crossing to zero. Early bolters are not usually kept for seed unless they are all you have; the habitual selection of these early-bolting plants will produce a variety which will tend to give smaller heads for a shorter period. To obtain the maximum amount of seed, plants should be harvested daily by shaking the seed heads into a large sack. If maximum yield is not essential, when two-thirds of the flowers are turning fluffy white, the plant can be cut and put out to dry on a large sheet of paper. The first seeds to ripen are the best fed, plumpest, and most suitable for seed stock. In wet climates, seeds may have to be harvested between rains. The whole plant can be harvested and hung upside down; the seeds will ripen as the thick stem continues to supply the necessary nutrients. After a complete drying, seed heads are rubbed between the hands. Three quarters of the mass you obtain will be chaff and white "feathers." Sieving with a small-gauged mesh will give reasonably clean seed. Please note: our heat-resistant Lettuce varieties, with the exception of Queensland Lettuce, are purchased from Sieger’s Seed Co., 8265 Felch Street, Zeeland, MI 49464 USA Phone: (616)772-4999 or 800-962-4999 FAX: (616)772-0333. If you need pure seed or seed in large quantity, you may wish to contact the company directly.
Pests and Diseases
If aphids infest your Lettuce, you may want to spray with an insecticidal soap. However, apply the soap to the plant only when it is young and stop applying it six weeks before harvest. For slug control, lay a board in the path beside the Lettuce in the evening. This will attract slugs the following morning as they look for a hiding place. Simply toss the board into the poultry yard or crush the slugs with your foot. Cutworms may be thwarted by surrounding seedlings with loose collars of stiff paper buried ½ inch into the soil, with one inch or more above ground to act as a barricade.
Cooking and Nutrition
Lettuce has a high water content and also contains vitamins A, C, and K, folacin, iron, calcium, fiber, potassium, and copper. Generally, the darker green the leaf is, the more vitamin A it contains.
- 莴 苣