Based on the color of the leaves, lettuce is divided into two types: green lettuce and purple lettuce. According to the growth status of the leaves, there are two types: loose leaf lettuce and head lettuce. The leaves of the former are scattered, while the leaves of the latter are fused into a ball. If further subdivided, there are three types of head lettuce. One is butter lettuce with obovate leaves, smooth leaves, soft texture, and slightly corrugated leaf edges; the other has obovate leaves with wrinkled leaves. Crisp leaf lettuce with a crisp texture and serrated edges. The latter is more commonly cultivated; the other is bitter-leaf lettuce with thick, oblong leaves, whole leaves, and semi-spherical shape. This kind of lettuce is rarely cultivated.

Heading lettuce likes cool climates, and the suitable growth temperature is 15-20°C. It is most suitable for environments with large temperature differences between day and night and low night temperatures. The suitable temperature for bulbing is 10-16°C. If the temperature exceeds 25°C, the high temperature inside the leaf bulb will cause necrosis and rot of the heart leaves and poor growth. The seed germination temperature is 15-20°C. If it is higher than 25°C, the seed coat will be blocked from absorbing water, resulting in poor germination. Lettuce needs to be treated at low temperature when sowing in summer. After soaking the seeds, put them in the cold room of the refrigerator to accelerate germination. Wait until the buds turn white before sowing. Loose leaf lettuce is relatively heat-tolerant, but it also grows poorly during high-temperature seasons. Lettuce prefers slightly acidic soil (pH 6-6.3 is best), and is best cultivated in sandy loam or clay loam soil with strong water retention and good drainage. Lettuce needs more nitrogen fertilizer, so more organic fertilizer should be applied as base fertilizer before planting, and no organic fertilizer should be applied during the growth process. There must be no lack of water during the growth period, especially during the head-setting period of lettuce. It needs sufficient water. If there is a lack of water early in the dry period, not only will the leaf heads be small, but the leaves will taste bitter and be of poor quality. However, the water should not be too much, otherwise the leaf balls will fall apart, affecting the appearance and quality, and may easily lead to the occurrence of soft rot and sclerotinia. Only with proper water and fertilizer management can we obtain high yield and high quality lettuce.

Lettuce is the common name for leaf lettuce, which belongs to the genus Lactuca of the Asteraceae family. It is an annual or biennial herbaceous crop and is also a popular vegetable in Europe and the United States. It is deeply loved by people.