Characteristics lettuce can be divided into green lettuce and purple lettuce according to the color of leaves. According to the growth state of leaves, there are two kinds of lettuce, lettuce and lettuce. The former leaves are scattered, while the latter leaves are spherical. If subdivided, there are three types of lettuce. One is butter lettuce with inverted oval leaves, smooth leaves, soft texture and slightly corrugated leaf edges; Another kind of crisp lettuce with inverted oval leaves, shriveled leaves, crisp texture and serrated leaves. The latter cultivation is more common; There is also a kind of bitter-leaf lettuce with thick, oval leaves, full leaves and semi-spherical shape, which is rarely cultivated.
The head lettuce enjoys a cool climate, and the suitable growth temperature is15-20℃, which is most suitable for the environment with large temperature difference between day and night and low temperature at night. The optimum temperature of nodulation is10-16℃, and when the temperature exceeds 25℃, the heart leaves will be necrotic and rotten due to high temperature inside the leaf bulb, and the growth will be poor. The germination temperature of seeds is15-20℃, which is higher than 25℃. Because the seed coat is blocked from absorbing water, the germination is poor. Lettuce should be treated at low temperature when sowing in summer. After soaking, it should be put in the refrigerator to accelerate germination, and then sowing should be carried out after the buds are white. Loose-leaf lettuce is more heat-tolerant, but it also grows poorly in high temperature season. The soil with slightly acidic lettuce (pH 6-6.3 is the best) is cultivated in sandy loam or clay loam with strong water retention and good drainage. Lettuce needs more nitrogen fertilizer, so organic fertilizer should be applied to the base fertilizer before planting, and no organic fertilizer should be applied during growth. Water shortage is not allowed during the growth period, especially during the heading period of lettuce, which requires sufficient water. If water shortage occurs early, not only the leaves are small, but also the leaves taste bitter and the quality is poor. However, there should not be too much water, otherwise the bulb will crack, which will affect the appearance quality and easily lead to soft rot and Sclerotinia sclerotiorum. Only proper water and fertilizer management can obtain high-yield and high-quality lettuce.
Key points of cultivation: Lailai is a cold vegetable, and its cultivation in the open field is mainly in spring and autumn. If it is to be supplied all year round, it should be produced in a combination of open field and protected field, which can basically meet the annual demand. In Shanghai, when cultivated in spring, seedlings are usually raised in cold beds from the end of/kloc-0 to the first ten days of February, and then planted in the first ten days of March. If the seedlings are raised in the open field in spring, they should be sown in early March and planted in early April. The spacing between rows and plants is generally 30 cm square, and 5000-6000 seedlings are planted every 666.7 square meters. Lettuce seeds are small, and generally 666.7 square meters can be planted by sowing 25 grams. Depending on the maturity of varieties, it takes 30-50 days from planting to harvesting. Autumn cultivation is often carried out in August, when sowing is in the hot season in Shanghai, the seeds must be soaked for 3-4 hours to make them fully absorb water, then wrapped in cloth and put into the freezer to accelerate germination. The temperature is generally controlled within the range of 5-10℃. After 4-5 days, 70-80% of the seeds can be sown when white buds are exposed. The seedbed should be fully watered and covered with wheat straw after sowing. If there is a sunshade net, it is more ideal to set up a shed for shade. When 60%-70% of the seedlings are unearthed, it is necessary to remove the wheat straw in time, but it is still necessary to shade it to prevent the seedlings from dying under high temperature. Sowing in autumn, because of the high temperature and large evaporation, the soil must be kept moist throughout the seedling stage, otherwise the seedling is not ideal. Lettuce grows fast and has a short growth period. Some varieties can be harvested more than a month after planting. The single plant weight of loose-leaf lettuce is 250-500g, and the growth period of head lettuce is longer than that of loose-leaf lettuce, and the single plant weight is generally 400-750g, and the late-maturing varieties with long growth period can reach more than1000g. The yield of 666.7 square meters of lettuce varies with varieties, usually1000-3000 kg.
Nutrition and Edible Lettuce is rich in water, and the water content per100g edible part is as high as 94%-96%, so raw food is crisp and refreshing, especially fresh and tender. Every100g of edible part also contains protein1-1.4g, carbohydrate1.8-3.2g, vitamin c10-15mg and some minerals. Lettuce also contains lettuce element, which has the functions of clearing away heat, diminishing inflammation and hypnosis. Lettuce is low in calories, and it is loved by people in today's world where slim body is advocated. The main eating method of lettuce is raw food, which is the main dish of western vegetable salad. The washed lettuce leaves are placed in a cold dish, and then served with other brightly colored vegetables or meat and seafood, which is a salad with good color, fragrance and taste. Wrapping steak, pork chop or fried rice with lard with leaves is also a widely used eating method. In addition, meat, poultry and other meat-based thick soups can be regarded as excellent soups when lettuce is put into the table and boiled immediately. In a word, lettuce can be eaten in various ways, so you can cook it according to your own taste.
Lettuce contains dietary fiber and vitamin C, which can eliminate excess fat, so it is also called slimming lettuce.
2, because its stems and leaves contain lettuce, it tastes slightly bitter, and has the effects of analgesia and hypnosis, lowering cholesterol, and adjuvant treatment of neurasthenia;
3. Lettuce contains active ingredients such as mannitol, which has diuretic and blood circulation promoting effects;