Cultivation techniques of lettuce in summer

Lettuce is the common name of leaf lettuce, which belongs to the genus lettuce of Compositae. It is an annual or biennial herbaceous crop. It is also a popular vegetable in Europe and the United States. Lettuce is native to the Euro-Mediterranean coast and is domesticated from wild species. The ancient Greeks and Romans ate it first. Lettuce has been introduced into China for a long time, and it is widely cultivated along the southeast coast, especially in the suburbs of big cities and in Guangdong and Guangzhou, especially in Taiwan. In recent years, the cultivation area has expanded rapidly, and lettuce has also entered the table of ordinary people from hotels and restaurants.

Morphological characteristics of lettuce

Lettuce annual or biennial herbs, 25-100 cm tall. The root extends vertically. Stem erect, solitary, distal panicle branched, all stem branches white. Basal leaves and lower stems large, undivided, oblanceolate, elliptic or elliptic-oblanceolate, 6-15 cm long and 1.5-6.5 cm wide, apex acute, shortly acuminate or rounded, sessile, base cordate or arrowhead-shaped semi-clasping, margin undulate or serrulate, acuminate upward, homomorphic or lanceolate to basal leaves and lower stems, leaves on lower branches of panicles and leaves on panicles very small. Ovate-cordate, sessile, base cordate or arrowhead-clasping, margin entire, all leaves glabrous on both surfaces.

Inflorescences numerous or extremely numerous, arranged in panicles at the top of stem branches. Involucral bracts ovoid, 1.1 cm long, 6 mm wide; involucral bracts 5-layered, outermost layer broadly triangular, ca. 1 mm long, ca. 2 mm wide, outer triangular or lanceolate, 5-7 mm long, ca. 2 mm wide, middle layer lanceolate to ovate-lanceolate, ca. 9 mm long, 2-3 mm wide, inner layer linear-elliptic, 1 cm long, ca. 2 mm wide, apex acute of all involucral bracts, glabrous outside. There are about 15 ligulate florets. Achenes oblanceolate, 4 mm long and 1.3 mm wide, compressed, light brown, with 6-7 veinlets on each side, apex acute into a fine beak, beak filiform, ca. 4 mm, as long as achenes. Crown hairs 2-layered, slender, scaberulous. The flowering and fruiting period is from February to September.

Cultivation techniques of lettuce in summer

First, select a good variety

The varieties of Caesar, Emperor, Xialu and Green Lake, which are heat-resistant and not easy to bolting, should be selected for planting lettuce in May and June.

Second, cultivate strong seedlings

1. Soaking seeds to accelerate budding. The seed of lettuce is small, the direct seeding technology is difficult to master, and the emergence uniformity is poor, so it is generally used to raise seedlings and transfer load. The nursery bed should be leveled and raked fine, with 25 grams per mu and 10 square meters of seedbed area. Soak the seeds to accelerate germination before sowing. First, soak in 20 ℃ of water for 4 hours, then dry the seeds in gauze and accelerate germination under the condition of 15 ℃ ~ 20 ℃. It can also be suspended on the surface of the well to promote germination at low temperature, or placed in a refrigerator of 5 ℃ ~ 10 ℃ for 24 hours, and then put the seeds in a cool place to moisturize and germinate, and then sow after the seeds are white.

2. Sowing and raising seedlings. Before sowing, the seedling bed is watered with bottom water, and after the water seeps down, the seeds are mixed with fine sand and sown, covering 0.3 cm of fine soil, and covered with sunshade nets or Reed curtains. Generally, the seedling age is about 25 days, the soil should be kept moist at the seedling stage, the sunshade net should be removed when the seedlings spit out their hearts, and they should be watered once to prevent the young roots of the seedlings from flushing out, and a thin layer of fine soil should be covered after watering. The seedlings were fixed when two true leaves were used, weeds in the bed were pulled out at the same time, and water was watered once, and the seedlings were planted in time when the seedlings grew to 4 or 5 true leaves.

III. Field management

1. Ploughing. Three to five days after planting, the soil moisture was preserved by ploughing in time, and 1-2 times of shallow ploughing was generally carried out before ridge closure to promote early root development.

2. Watering. During the growing period, watering should be uniform, small water should be watered frequently, and the surface of the border should be kept moist and not too dry and wet.

3. Topdressing. Because lettuce is mainly raw food, topdressing does not apply human manure or chicken manure, mainly chemical fertilizer, generally topdressing 3 times 4 times, 15 days after slow seedling, rosette stage, heart stage, each mu of urea 5-8 kg, with water application, but not too much, to prevent lettuce dry heartburn. During the growing period, potassium dihydrogen phosphate can be properly sprayed on the leaves to improve disease resistance and edible quality.

Fourth, pest control. There are few diseases and insect pests in lettuce, only a few aphids, which can be controlled in time with high-efficiency and low-toxic pesticides.

5. Harvest in batches

Because the planting density of lettuce is relatively high and the staple food is crisp and tender leaves, the loose leaf balls can be harvested and listed one after another 30 days after planting.