(1) Seedlings are typically started right after the beginning of autumn, with the latest planting date being no later than August 15. Delaying the nursery period can cause a delay in both planting and fruiting, which may affect the melon's maturity. Before sowing, watermelon seeds are first soaked to enhance germination, as the temperature is favorable at this time. After soaking, the seeds are covered with mulch, and a new plastic rainproof film and shade net are installed. On sunny mornings, the shade net is put up at 8 a.m., and removed at 4 p.m. However, it is not used on rainy days. Common seedling diseases include blight and damping-off. A mixture of chlorothalonil (600 times diluted) and mancozeb (1000 times diluted) can be sprayed every 5–7 days, sometimes even twice or three times. During the seedling stage, pests such as larvae, diamondback moths, and noctuid moths may appear. To control them, a 1500-fold dilution of dimethoate and thiodicarb can be applied. The seedlings are ready for transplanting after 20–25 days, when they have developed three leaves and one heart.
(2) Soil preparation is crucial for growing watermelons under greenhouse conditions. The soil should be plowed, leveled, and ridged, ensuring good drainage. The ridge width should be between 2.5 to 3.0 meters, with ditches 35 cm wide. A nutrient ditch, 50 cm wide and 40 cm deep, is prepared for applying decomposed organic fertilizer, such as pig manure, at a rate of 3,000 kg per 667 square meters. Additionally, 75 kg of NPK fertilizer is added and mixed into the soil before covering the ditch. Some fertilizer is also applied directly on the soil surface—about 1,500 kg per 667 m². This helps the adventitious roots on the watermelon vines absorb nutrients more effectively, supporting healthy plant growth.
(3) Autumn watermelon planting should take place at the end of August and early September. Approximately 800 rows are planted per 667 square meters, with each plant placed on the nutrient ridge. When planting, the seedlings are carefully removed from their containers, and the planting depth should be slightly deeper than the original soil level. After planting, the area is immediately watered, and a herbicide like Dore is sprayed on the surface at a rate of 100 ml per 667 square meters, mixed with 50 kg of water. The field is then covered with a plastic film. To prevent damage from heavy rain, the greenhouse top film is pulled over immediately after planting.
(4) The ideal temperature for post-planting watermelon management is between 25–30°C. If temperatures drop too low, growth slows down; if they rise too high, virus diseases may occur. Nighttime temperatures should not fall below 18°C, and daytime temperatures should not exceed 32°C. From late August to early September, nighttime temperatures begin to drop, so the greenhouse film is closed at night. On sunny mornings, the greenhouse vents are opened at 8 a.m., and closed again at 4 p.m. As temperatures continue to decrease, the morning vent opening time is gradually delayed, and the closing time in the afternoon is advanced. About a week after planting, the vines are trained, and two main vines are selected. Once the flowers appear, artificial pollination is necessary since there are no pollinators inside the greenhouse. Pollination should be done between 6 a.m. and 10 a.m., preferably on the second female flower. After pollination, the vine tip is pinched off to direct nutrients to the developing fruit. When the melon reaches about 1 kg, it is time to perform parallel fruit setting, fixing the shape and position of the melon. Watermelons usually mature in 6–7 weeks and are ready for harvest.
(5) Harvesting generally occurs 40 days after the fruit has ripened, which is about 10 days later than traditional open-field watermelons. Autumn watermelons are more suitable for storage. After picking, they can be stored at room temperature for 15–20 days without significant quality loss.
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