When to Sow and Transplant the Diet-Friendly Vegetable Lettuce? A Detailed Guide to Growing Techniques

Lettuce, also known as stem lettuce and leaf lettuce, is a common annual or biennial herbaceous crop in the southeastern coastal regions. It is highly favored by consumers because it contains a variety of vitamins and minerals that the human body can absorb, and its planting area in China has been 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. At the same time, add 50 grams of urea and 500 grams of superphosphate per cubic meter of bed soil. After mixing evenly and sifting, spread it evenly on the seedling bed to a thickness of 5 cm (when pricking out seedlings, the seedling bed soil should be spread to a thickness of 10 cm).

II. Seedling Raising

1. Seed treatment and sowing time: Spring cultivation is generally from February to April, and seedlings are raised by sowing dry seeds directly. For summer and autumn cultivation, sowing is from June to August. When weather conditions make germination difficult, the seeds need to be soaked and then germinated at 15°C-22°C before sowing.

2. Sowing: Before sowing, water the seedling bed thoroughly. After the water seeps down, scatter a 0.5 cm layer of fine soil, and then sow. Generally, the sowing rate is 10 grams per square meter of seedling bed. After sowing, cover with 1 cm of fine moist soil and cover with plastic film to retain moisture. Remove the film after seedlings emerge in 3-5 days. For summer and autumn seedling raising, pay attention to rain protection and shading to cool down. Keep the seedling bed temperature at 18°C-20°C. When the nighttime temperature exceeds 15°C, seedling growth is adversely affected. When the seedlings grow one true leaf, prick out seedlings at a spacing of 6-8 cm between plants and rows, with the pricking-out bed soil 10 cm thick. Throughout the seedling stage, prevent spindly, leggy seedlings caused by high temperatures and stiff 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 5,000 kg of decomposed high-quality farmyard manure and 20 kg of compound fertilizer per mu. After broadcasting, plow 15-20 cm deep, then make raised beds 1 m wide and 10-15 cm high. In winter and spring, to increase soil temperature, cover with film 15 days in advance to warm the ground. When the soil temperature stabilizes at 8°C, seedlings can be transplanted.

When transplanting, leaf lettuce can be planted somewhat densely, with a row spacing of 20-25 cm. For head lettuce, the row spacing is 30-40 cm. Transplant with a soil ball. The planting 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. For head lettuce, appropriately restrain growth for 5-7 days, then carry out topdressing and watering. Apply 10 kg of urea per mu, applying fertilizer with irrigation water, and keep the soil moist. In addition, for head lettuce, at the early stage of heart leaf curling, 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, ventilate to cool down or take shading measures. At the same time, lettuce is also afraid of waterlogging, so water must not accumulate in the beds, and drain promptly after rain. After hot summer rain, it must be irrigated with cold water in time.

In the middle and late stages of lettuce growth, to keep the rosette leaves from declining and allow the head leaves to rapidly close and grow 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

Harvest when the leaves have fully grown, are green, thick, crisp, and tender; at this time, yield and commercial value are high. For head lettuce, harvest when the head feels somewhat firm under pressure and the head density is moderate. Harvesting methods: For leaf lettuce, you can break off large leaves and leave small ones, tie the harvested leaves into bundles for market, or cut the whole plant. For head lettuce, cut it off at the ground surface, remove the outer old leaves, and leave 3-4 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 light yellow spots. When humid, white mold grows on the underside of the leaves. In the later stage, the spots merge into patches. When dry, the leaves turn yellow-brown and wither.

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-20°C, with cloudy, rainy, and humid conditions and a water layer or water droplets on the plant surface, it is extremely susceptible to infection.

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

(2) Stem rot

① Symptoms: It damages leaves and petioles. Leaves and heads show wet rot and net-like mycelium. Petioles near the ground have brown necrotic spots. 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% procymidone (trade name: procymidone) wettable powder at 1500 times dilution.

2. 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 drench with 90% trichlorfon at 800 times dilution.