Detailed Explanation of Four-Season High-Yield Cultivation Techniques for Celtuce

1. Variety selection: For overwintering celtuce and spring celtuce, choose varieties that are cold-resistant, highly adaptable, and slow to bolt, such as Cold-Resistant White Leaf Tip, Cold-Resistant Two-White-Skin, and Bitter Lettuce Leaf. For summer and autumn celtuce, choose heat-resistant early-maturing varieties, such as Heat-Resistant White Leaf Tip, Bitter Lettuce Leaf, Heat-Resistant Large Large Flower Leaf, Extra Heat-Resistant Two-White-Skin, and Oil Wheat Lettuce.
　　
2. Determining sowing dates: For spring celtuce, raise seedlings in greenhouses from December to March, and raise seedlings in open fields from mid-February to late March. For summer celtuce, cultivate in open fields from April to mid-to-early May, and from late May to July use shade net covering, with direct sowing or high-density planting. For autumn celtuce, sow from July to September under shade net covering, and raise seedlings for transplanting. For overwintering celtuce, raise seedlings in open fields from October to November.
　　
3. Raising strong seedlings:
3.1 Soil preparation. Choose a high, dry, well-drained plot 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 deep plow, 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 daily; they will germinate in 3-4 days. Another method 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 place them in a cool place, and they will germinate in 2-3 days.
3.3 Sowing. For spring celtuce, when sowing seedlings in greenhouses, 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, cover tightly with film, and add shade net or straw mat covering at night for insulation. For open-field seedling raising, add a small arch shed cover. Before the seedlings emerge, uncover late and cover early, do not ventilate, and raise the bed temperature. After the seedlings emerge, ventilate appropriately, maintaining the bed temperature at 12-20°C during the day and 5-8°C at night. Uncover the shade net early and cover it late. Thin seedlings once when there are 2-3 true leaves, with a seedling spacing of 4-5 cm. Increase ventilation to harden the seedlings 5-6 days before transplanting.
For summer celtuce, choose a cloudy day for sowing. From April to mid-to-early May, sow wet seeds and cover with film, then remove it after emergence. From late May to mid-to-early July, cover with a small arch shed or flat shed with shade net until emergence or 2 true leaves. On heavy rainy days, cover with shade net to prevent rain from washing away the soil. Sow 5-10 g per 10 sq m. Thin seedlings once before 2 true leaves, and 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 from transplanting, apply decomposed dilute manure water together with watering. On rainy days, clear the ditches and drain waterlogging. About 15 days before transplanting, apply 0.50% urea water once. About 25 days after final thinning or transplanting, tender plants can be harvested successively for market.
For autumn celtuce, 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 net, sowing germinated seeds or wet seeds. Before emergence, use double-layer floating covering on the seedbed soil; after emergence, cover with silver-gray shade net. Water and fertilize in the morning and evening, keep the bed soil moist, and timely weed and thin seedlings.
　　
4. Field planting and management:
When field planting, choose loam soil with good drainage, and apply 4000-5000 kg of decomposed organic fertilizer per mu. Deep plow and level, and make high beds 1.20-1.50 m wide. Before lifting seedlings, first water the seedbed.
For spring celtuce, field plant when the seedling age is 25-30 days and there are 5-6 leaves, with a plant and row spacing of 20 cm × 27 cm, and a depth suitable for burying to the base of the first leaf stalk, then water after planting to settle the roots. For leaf marketing, use a plant and row spacing of 15 cm × 20 cm. For plastic film mulching cultivation, apply enough base fertilizer at one time and cover the plastic film well, and drain water on rainy days to prevent waterlogging. For greenhouse and open-field cultivation, choose clear warm weather to cultivate 1-2 times, water and topdress in a timely manner, apply dilute manure frequently in the early stage, keep the bed surface moist, and when the plants basically close the rows, tender plants can be marketed. For stem production, apply 15 kg of urea per mu by watering 1-2 times.
Autumn celtuce. Field plant when the seedling age is 25 days, with a plant and row spacing of 25 cm × (30-35) cm; for tender plant marketing, use a plant and row spacing of 15 cm × 20 cm. After field planting on a cloudy day or in the afternoon, water promptly to settle the roots, and use a greenhouse, small arch shed, or flat shed covered with shade net, then remove it after the seedlings recover. Cultivate less and shallowly, apply dilute manure frequently, keep the soil moist, and around the row-closing stage, apply 3000-4000 kg of 30-40% decomposed human and livestock manure per mu or 15 kg of urea 2-3 times.
Overwintering celtuce. The base fertilizer in the seedbed should not be too abundant. When the seedling age is about 40 days, field plant with plastic film mulching, with a plant and row spacing of (30-35) cm × (30-40) cm. After survival, apply 1-2 times of dilute manure water as topdressing. If marketing as mature plants the following year, pay attention to hardening seedlings before overwintering, do not apply fertilizer and water too frequently, and prevent excessive vegetative growth during the seedling stage. Apply one heavy application of antifreeze fertilizer and water before freezing. The following spring, timely remove weeds, cultivate shallowly once, and increase topdressing concentration from low to high. After the stem base begins to expand, reduce the number and concentration of topdressing. For plastic film and greenhouse cultivation, apply enough base fertilizer and pay attention to ventilation management.
　　
5. Pest and disease control
For celtuce downy mildew, alternately spray 75% chlorothalonil wettable powder at 600-800 times, or 58% Ridomil at 500 times, or 40% phosethyl-Al wettable powder at 200 times, or 72.20% propamocarb aqueous solution at 800 times. For celtuce viral disease, timely control aphids with omethoate or pirimicarb. At the early stage of disease, spray 20% Virus A wettable powder at 500 times, or Antiviral Agent No. 1 aqueous solution at 300 times, or 83 resistance inducer at 100 times, using them in rotation. For celtuce sclerotinia rot, use 70% thiophanate-methyl wettable powder at 700 times, 50% procymidone wettable powder at 1500 times, and 50% iprodione wettable powder at 1000 times in rotation. For celtuce black spot, spray 50% iprodione wettable powder at 1500 times, 40% captan wettable powder at 400 times, 70% fosetyl-Al · mancozeb wettable powder at 500 times, and 75% chlorothalonil wettable powder at 600 times.
　　
6. Harvesting and seed collection
Tender plants can be harvested for market at any time before the stem is fully thickened. When the top of the celtuce is level with the tip of the highest leaf, it is the suitable time to harvest the celtuce stem. For autumn celtuce, 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 spray 2500 mg/kg maleic hydrazide 2 times every 5 days when the base is thickening.
For celtuce seed collection, it is best to save seeds from overwintering spring celtuce. Keep seed plants isolated by about 1000 m between varieties. Select and retain plants that grow vigorously and have the characteristics of this 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 side branch growth. During flowering, appropriately remove some branches, insert support stakes to prevent lodging, and do not let the soil lack water during the flowering period. Reduce irrigation after the flowers fade. 20-25 days after flowering, when the leaves of the seed plants turn yellow normally, the seeds are brown or silver-gray, and white pappus appears, harvest promptly.