How to Grow Lettuce in a Greenhouse? The Latest Planting Technique Tutorial

Lettuce planted in late autumn generally comes to market in early March after the Spring Festival. At this time lettuce is in the middle of the concentrated vegetable harvest season, so prices are low and profits are poor. Growing winter lettuce in plastic greenhouses gives high yields and good quality, and when it comes to market during the Spring Festival the economic returns are remarkable. Now the editor will introduce greenhouse lettuce growing techniques to everyone.

Pre-planting Preparation for Lettuce

1. Field selection: Lettuce should not be grown continuously on the same land; rotation with gramineous crops is best, and paddy field soil is generally preferred. The field should be on high ground with convenient drainage and irrigation.

2. Variety selection: Choose cold-tolerant, frost-tolerant early-maturing varieties. Such lettuce varieties as Kexing No. 1, Zhongdu Cold-tolerant Erbaipi, Xuelisong, and Guasihong.

3. Timely sowing: Generally sow around September 10, give or take 2 days, using about 50g of seed per 1 mu; the seedling age is 30—50 days, and the transplanting period is before October 15.

Transplanting and Film Covering for Lettuce

1. Preparation before transplanting. One week in advance, plow deep and let the soil bake, and apply all the base fertilizer at once. Apply 2500—3000 kg of decomposed organic fertilizer and 150 kg of NPK compound fertilizer per 1 mu, then prepare the land and make beds, with a bed surface width of 4—8 chi.

2. Transplanting density: The row spacing for transplanting is 40 cm and the plant spacing is 35 cm, so about 5000 plants can be transplanted per 1 mu.

3. In mid-December, once the cold winter has set in, the plants grow slowly and are prone to low-temperature freezing damage, showing dry leaves, hard dry stems, and poor quality. In order to create a good environmental condition for the growth of lettuce plants, greenhouse film should be covered promptly to keep them warm.

Growing Management of Lettuce

1. Transplanting: Right after transplanting, water with 5% human and livestock manure water to settle the roots. 5—7 days later, apply once 10% human and livestock manure water plus 0.2% urea to promote seedling growth, and carry out one inter-row cultivation of the soil. When the small heart begins to form, the fertilizer requirement increases, so apply once every 7 days a mixed solution of livestock manure water plus 0.3% urea and 0.3% potassium chloride to promote early growth of the lettuce. At the early stage of stem expansion, make holes between the plants and apply 50g of a mixed fertilizer of NPK compound fertilizer and oil cake in a 7:3 ratio. After covering with film, attention should be paid to controlling fertilizer. From late December to January of the following year, apply a heavy stem-elongation fertilizer once, generally by watering with 30% human and livestock manure water plus 0.5% urea and 0.5% potassium chloride mixed solution.

2. Temperature and humidity control inside the greenhouse: Temperature and humidity management is the key technical measure for the success or failure of winter lettuce in greenhouses. According to the growth needs of the plants and climate changes, it is broadly divided into two stages of management: in the early stage, prevent high temperatures from causing spindly bolting growth. In the later stage, the main task is to keep warm and prevent freezing, while also paying attention to venting to remove moisture. Generally, after the film is covered, if the temperature is too high, the side film should be lifted to cool things down. As the temperature drops later, the side film is no longer lifted. Only the doors at both ends of the greenhouse are opened to vent and cool. In frost and snow weather, vent to remove moisture once every 1—2 days, and simply keep the air inside the greenhouse fresh.

3. Application of growth regulators: After transplanting and recovery from seedling stage, if the temperature is on the high side, the seedlings tend to bolt, so a 50mg/l solution of mepiquat chloride or paclobutrazol can be sprayed once to control internode elongation. When the small heart begins to form, spray with a 100mg/l aqueous solution of “481” to increase functional leaves and promote the formation of photosynthetic products. During the stem expansion period, spraying with 25mg/l “Shifengle” or 600-fold “Jintianbao” nutrient liquid fertilizer can further increase yield and improve quality.

Disease Control for Lettuce

Greenhouse lettuce, being under long periods of high humidity, is susceptible to downy mildew and sclerotial soft rot. In addition to strengthening management inside the greenhouse, microbial control and chemical control should be combined. Before infection, spray 500—600-fold “Yian Shenli” or “Yiyijiu” microbial liquid 2—3 times to improve the disease resistance of the plants. After infection, for downy mildew spray 70% mancozeb-plus 500-fold, and for sclerotial soft rot spray 50% carbendazim 400-fold plus 70% mancozeb 500-fold, or 50% thiophanate-methyl 800-fold plus 50% procymidone 1000-fold. Chlorothalonil smoke agents or procymidone smoke agents can also be used for control.