When to Sow and Transplant Weight-Loss Lettuce? A Detailed Guide to Growing Techniques

Lettuce, also known as wosun (celtuce) and leaf lettuce, is a common annual or biennial herbaceous crop in the coastal areas of Southeast China. It is favored by consumers because it contains a variety of vitamins and minerals that are readily absorbed by the human body. At present, its planting area in China is increasing year by year. So in what season is lettuce sown? When is it transplanted? What are the growing techniques?

I. Soil Selection

For seedling raising, beds can be made and sown directly in the production field. The seedling bed soil consists of 50% garden soil and 50% decomposed farmyard manure, and for each cubic meter of bed soil, add 50 g of urea and 500 g of superphosphate. After mixing and sieving, spread it evenly on the seedbed to a thickness of 5 cm (when pricking out seedlings, the seedbed soil should be spread to a thickness of 10 cm).

II. Seedling Raising

1. Seed treatment and sowing time: For spring cultivation, it is generally from February to April, and dry seeds are sown directly for seedling raising. For summer and autumn cultivation, sowing is from June to August. When the weather makes germination difficult, the seeds need to be soaked and then germinated at 15°C to 22°C before sowing.

2. Sowing: Before sowing, water the seedbed thoroughly to provide bottom moisture. After the water seeps down, scatter a 0.5 cm thick layer of fine soil, and then sow. Generally, the sowing rate is 10 g per square meter of seedbed. After sowing, cover with 1 cm of fine moist soil and cover with plastic film to retain moisture. After seedlings emerge in 3 to 5 days, remove the plastic film. For summer and autumn seedling raising, pay attention to rain protection and shading to lower the temperature. The seedbed temperature should be controlled at 18°C to 20°C; when the nighttime temperature exceeds 15°C, seedling growth is unfavorable. When the seedlings grow one true leaf, prick out the seedlings at a plant-to-row spacing of 6 to 8 cm, and the soil thickness of the pricking-out bed should be 10 cm. Throughout the seedling stage, prevent thin, tall, leggy seedlings caused by high temperatures and stiffened seedlings with small cotyledons and short hypocotyls formed under drought conditions.

III. Transplanting

Lettuce has a shallow root system and absorbs nutrients through fibrous roots, so it requires soil with good permeability. Before transplanting, first prepare the land and apply fertilizer. Apply 5000 kg of decomposed high-quality farmyard manure and 20 kg of compound fertilizer per mu. After broadcasting, plow 15 to 20 cm deep, then make raised beds 1 m wide with a bed height of 10 to 15 cm. In winter and spring, to raise the ground temperature, cover with plastic film 15 days in advance to warm the soil. When the ground temperature stabilizes at 8°C, the seedlings can be transplanted.

When transplanting, loose-leaf lettuce can be planted somewhat densely, with a row-to-plant spacing of 20 to 25 cm, while head lettuce has a row-to-plant spacing of 30 to 40 cm. Transplant with a soil ball. The transplanting depth should be such that the soil ball is level with the ground surface. After planting, water thoroughly in time to promote rapid recovery. Generally, the seedlings recover and survive 6 days after planting.

IV. Field Management

After the seedlings recover, topdressing and watering can begin. Head lettuce can be given a controlled seedling treatment for 5 to 7 days, and then topdressing and watering can be carried out, applying 10 kg of urea per mu with the irrigation water to keep the soil moist. In addition, for head lettuce, in the early stage when the heart leaves curl inward, spray the leaves with 0.2% urea and 0.2% monopotassium phosphate.

Lettuce is not tolerant of high temperature and high humidity. When the temperature exceeds 25°C, ventilation should be provided to lower the temperature or shading measures should be taken. At the same time, lettuce is also afraid of waterlogging, so water must not accumulate in the beds, and drainage should be carried out promptly after rain. After hot summer rain, it must be irrigated promptly with cold water.

In the middle and late stages of lettuce growth, in order to keep the rosette leaves from aging and allow the head leaves to close and grow rapidly to form firm heads, continuous and even water supply is needed to avoid head cracking or open growth during heading. In potassium-deficient plots, pay attention to applying potassium fertilizer during this period. Stop watering 5 days before harvest.

V. Timely Harvest

When the leaves have fully grown, are green, thick, and crisp-tender, harvesting at this time gives high yield and good commercial value. For head lettuce, if the head feels somewhat resistant when pressed firmly and the head firmness is moderate, it can be harvested. The harvesting method is: for loose-leaf lettuce, large leaves can be broken off while small leaves are left, and the harvested leaves can be tied in bundles for market, or the whole plant can be cut off. For head lettuce at harvest, cut it off at the ground surface, remove the outer old leaves, and keep 3 to 4 outer leaves around the head before packaging for market.

VI. Pest and Disease Control

1. Diseases:

(1) Downy mildew

① Symptoms: It damages leaves. Diseased leaves have pale yellow spots, and white mold grows on the underside of the leaves when humid. In the later stage, the spots merge, and when dry, the leaves turn yellow-brown and dry up.

② Transmission route and conditions for onset: It is a fungal disease. Seeds and diseased plant residues can carry the pathogen, and the pathogen spreads through wind and rain. The pathogen can directly invade the plant body through the epidermis or stomata. When the temperature is 15°C to 20°C, with cloudy and rainy, humid conditions and a water layer or water droplets on the plant surface, infection is extremely likely.

③ Control measures: Implement crop rotation of more than two years, select disease-resistant varieties, prevent high humidity in the field, use 50% carbendazim wettable powder at 800 times dilution for prevention, and at the early stage of disease, 50% metalaxyl wettable powder has a relatively good effect.

(2) Stem rot

① Symptoms: It damages leaves and leaf stalks. The leaves and heads show wet rot and have a net-like mycelium. The leaf stalks near the ground have brown necrotic spots, and when humid, brown juice oozes out. When dry, they become brown sunken spots, sometimes with brown sclerotia.

② Transmission route and conditions for onset: It is a fungal disease. Diseased plants, seeds, and soil can carry the pathogen, and the pathogen spreads through rainwater, irrigation water, and field operations. It is prone to occur in fields with temperatures above 20°C, high air humidity, or standing water.

③ Control measures: Select disease-resistant varieties, use 10% salt water to select seeds, strengthen field management, prevent high humidity and excessive nitrogen, and spray 50% Sumilex (trade name procymidone) wettable powder at 1500 times dilution.

2. Insect pests

Lettuce pests include aphids, thrips, and cutworms. For aphids, 2.5% imidacloprid has a relatively good control effect; for thrips, 75% dimethoate emulsifiable concentrate at 1000 times dilution can be used; for cutworms, grass piles can be used for trapping and killing, or irrigation with 90% trichlorfon at 800 times dilution can be used.