A Detailed Explanation of Lettuce Cultivation Techniques and Management Key Points

Lettuce Growing Environment

Lettuce is sensitive to soil acidity and alkalinity, and is suitable for planting in slightly acidic soil.

Lettuce has a shallow root system, weak absorption capacity, and a relatively high demand for oxygen; sandy loam and loam are best for growing lettuce.

Lettuce Cultivation Techniques

1. Variety Selection

For overwintering lettuce and spring lettuce, choose varieties that are cold-tolerant, highly adaptable, and slow to bolt, such as cold-tolerant White Leaf Tip, cold-tolerant Erbaipi, and Ku Mai Ye (bitter lettuce leaf). For summer and autumn lettuce, choose heat-tolerant early-maturing varieties, such as heat-tolerant White Leaf Tip, Ku Mai Ye, heat-tolerant Large Large Flower Leaf, extra heat-tolerant Erbaipi, and oilseed lettuce.

2. Determining Sowing Time

Spring lettuce: raise seedlings in a greenhouse from December to March, or raise seedlings in open fields from mid-February to late March. Summer lettuce: cultivate in open fields from April to mid-May; from late May to July, use shade netting coverage and direct sowing or high-density planting. Autumn lettuce: from July to September, use shade netting coverage for sowing, then raise seedlings and transplant. Overwintering lettuce: raise seedlings in open fields from October to November.

3. Raising Strong Seedlings

3.1 Soil preparation:

Choose a plot with high, dry terrain and good drainage as the seedbed. Apply 4000-5000 kg of decomposed organic fertilizer or 500 kg of compound fertilizer per mu as base fertilizer 5-7 days before sowing. Apply before land preparation, then plow deeply, level and finely rake, and cover with plastic film while waiting to sow.

3.2 Seed treatment:

For sowing from May to September, because of the hot high temperatures, seeds germinate with difficulty, so low-temperature germination promotion is needed before sowing. Soak the seeds in cool water for 6-7 hours, then wrap them in a wet cloth and keep them at 20-25°C to promote germination until 80% of the seeds show white sprouts. Alternatively, soak the seeds in cool water for 1-2 hours, wrap them in a wet cloth, place them 30 cm below the water surface in a well, and sprinkle water 1-2 times a day; they will germinate in 3-4 days. Another option is to soak the seeds for 24 hours, wrap them in a wet cloth, place them in a refrigerator or freezer at -3 to -5°C for 24 hours, then keep them in a cool place, and they will germinate in 2-3 days.

3.3 Sowing:

For spring lettuce, when raising seedlings in a greenhouse, first uncover the film on the seedling bed, water thoroughly, and after the water seeps down, mix the seeds with a small amount of fine sand or fine soil, stir evenly, and broadcast sow. Sow 25-30 g of seeds per 10 sq m of seedbed. After sowing, cover with 0.30-0.50 cm of soil, seal the film tightly, and add shade netting or straw mats at night for insulation. For open-field seedling raising, add a small arch shed. Before the seedlings emerge, uncover the coverings late and cover early, and do not ventilate, to raise the bed temperature. After the seedlings emerge, ventilate appropriately, keeping the bed temperature at 12-20°C during the day and 5-8°C at night. Uncover the shade netting early and cover it late. Thin once when there are 2-3 true leaves, with a seedling spacing of 4-5 cm. 5-6 days before transplanting, increase ventilation to harden the seedlings.

For summer lettuce, choose an overcast day for sowing. From April to mid-May, sow wet seeds and cover with film, then remove it after emergence. From late May to mid-July, cover with shade netting using a small arch shed or flat shed until emergence or 2 true leaves. On heavy rainy days, cover with shade netting to prevent rain from washing them away. Sow 5-10 g per 10 sq m. Thin once before 2 true leaves, and thin once at 4-5 true leaves, with a seedling spacing of 10 cm. Strong seedlings can also be planted at high density with a plant and row spacing of about 10 cm. After each thinning, final thinning, and recovery after transplanting, apply decomposed dilute manure water together with watering. On rainy days, clean ditches to drain waterlogging, and about 15 days before planting, water once with 0.50% urea solution. About 25 days after final thinning or transplanting, young plants can be harvested successively for market.

For autumn lettuce, before sowing, first water the bed until wet and thoroughly soaked. After sowing, pour on a layer of decomposed pig manure residue at 30-40% concentration and cover with a thin layer of rice straw, or cover with black shade netting, and sow germinated seeds or wet seeds. Before emergence, use double-layer floating coverage on the seedbed soil; after emergence, cover with silver-gray shade netting. Water with liquid fertilizer morning and evening, keep the seedbed soil moist, and weed and thin in time.

4. Planting and Management

When planting, choose loam with good drainage and apply 4000-5000 kg of decomposed organic fertilizer per mu. Plow deeply and level, and make high beds 1.20-1.50 m wide. Before lifting the seedlings, first water the seedbed.

For spring lettuce, plant when the seedlings are 25-30 days old and have 5-6 leaves, with a plant and row spacing of 20 cm × 27 cm, and a depth that buries up to the base of the first leaf stalk; after planting, water to settle the roots. For marketing as leaves, use a plant and row spacing of 15 cm × 20 cm. For plastic film mulching cultivation, apply enough base fertilizer at one time, cover the plastic film well, and drain water on rainy days to prevent waterlogging. For greenhouse and open-field cultivation, choose warm, clear weather to cultivate 1-2 times, water and topdress in good time, and in the early stage apply dilute manure frequently to keep the bed surface moist; when the plants basically close the rows, they can be marketed as young plants. For those grown for the stem, apply 15 kg of urea per mu 1-2 times.

For autumn lettuce, plant when the seedlings are 25 days old, with a plant and row spacing of 25 cm × (30-35) cm; for marketing as young plants, use a plant and row spacing of 15 cm × 20 cm. Choose an overcast day or the afternoon for planting, then water in time to settle the roots, and use a greenhouse, small arch shed, or flat shed covered with shade netting, removing it after the seedlings recover. Cultivate less and shallowly, apply dilute manure frequently, and keep the soil moist. Around the period when the plants close the rows, apply 3000-4000 kg of 30-40% decomposed human and animal manure per mu or 15 kg of urea 2-3 times.

For overwintering lettuce, the seedbed base fertilizer should not be too abundant. When the seedlings are about 40 days old, plant with plastic film mulching, with a plant and row spacing of (30-35) cm × (30-40) cm. After survival, topdress 1-2 times with dilute manure water. If marketing as mature plants the following year, attention should be paid to hardening the seedlings before overwintering; fertilizer and water should not be applied too frequently, to prevent excessive growth during the seedling stage, and before freezing, apply a heavy application of antifreeze fertilizer water once. In the following spring, remove weeds in time, cultivate shallowly once, and increase topdressing concentration from low to high. After the stem base begins to expand, reduce the number of topdressings and lower the concentration. For cultivation with plastic film and greenhouses, apply enough base fertilizer and pay attention to ventilation management.

5. Harvesting and Seed Production

Before the stem is fully enlarged, young plants can be harvested at any time for market. When the top of the lettuce is level with the tip of the highest leaf, it is the suitable time to harvest the lettuce stem. For autumn lettuce, in order to extend the marketing period and delay harvest, you can pinch off the growing point and flower buds by hand on a sunny day, or starting from the rosette stage, spray 350-500 mg/kg chlormequat 2-3 times every 5-7 days, or when the base is enlarging, spray 2500 mg/kg maleic hydrazide 2 times every 5 days.

For lettuce seed production, it is best to save seed from overwintering spring lettuce, and seed plants should be isolated by about 1000 m between varieties. Select and keep plants that grow robustly and have the characteristics of the variety; after thinning, maintain a plant and row spacing of more than 33 cm square, remove old leaves, increase fertilizer and water, and earth up to promote lateral branch growth. During flowering, appropriately remove some branches, insert support stakes to prevent lodging, and do not let the plants lack water during the flowering period; after the flowers fade, reduce irrigation. 20-25 days after flowering, when the leaves of the seed plant turn yellow normally and the seeds are brown or silver-gray with white pappus, harvest in time.