Sharing Experience in High-Efficiency Cultivation of Watermelon in Double Greenhouses

I. Selecting Good Varieties and Raising Strong Seedlings  In recent years, the high-quality gift watermelon varieties cultivated in coastal areas mainly include Zaochun Hongyu, Hong Xiaoyu, Huang Xiaoyu, Te Xiaofeng, Xiaolan, etc., paired with medium-fruit-type varieties Jingxin No. 1, Jingxin No. 2, and Zaojia (8424). Melon farmers in coastal areas generally carry out seed soaking and sprouting in early to mid-January, using electric heating wires (80-100 watts per sq m) and plug trays with light substrate for seedling raising in greenhouses. During the seedling stage, attention should be paid to regulating temperature and humidity, and timely spraying of 75% chlorothalonil wettable powder 800-fold solution + 70% thiophanate-methyl wettable powder 800-fold solution to prevent seedling diseases caused by low temperature and high humidity in early spring. Moderately harden the seedlings 5-7 days before transplanting. The seedling age is 30 days, with the 2-leaf-1-heart stage as the standard for transplanting seedlings.

II. Reasonable Close Planting and Multi-Layer Covering  Watermelon should preferably be cultivated in sandy loam soil where cucurbit crops have not been grown within 3 years and with no pollution sources. Build double greenhouses 30 days before planting and cover with drip-free film to increase soil temperature. The inner greenhouse is 4.5 m wide, with a 5 m wide top film and 1 m wide skirt film; the outer greenhouse is 5 m wide, with a 6 m wide top film and 1 m wide skirt film; the spacing between the top agricultural films of the inner and outer greenhouses is 20-25 cm, and the spacing between the bottom edge agricultural films is 15-20 cm. The greenhouse top height is 1.6-1.8 m, and the length is 50-150 m. Make beds in the greenhouse 10 days before planting and spray herbicide. The bed width is 2 m, and the central walkway is 0.5 m wide. Apply 100 ml of 72% Duer or 50 ml of 96% Jinduer or 100 ml of 48% butralin (dibutalin) per mu mixed with 40 kg of water and spray evenly on the bed surface to prevent weeds, then lay plastic film flat to preheat the soil. Using double greenhouses + small tunnels + plastic film mulching to cultivate watermelon, transplant in early to mid-February when the soil temperature at 10 cm underground in the greenhouse is above 12°C and the minimum temperature is above 8°C, planting 700-750 plants per mu, water sufficiently for seedling recovery, seal the planting holes well, cover with small tunnel film, and close the greenhouse to form 4-layer film covering. III. Applying Sufficient Base Fertilizer and Timely Topdressing  For pollution-free cultivation of high-quality watermelon, sufficient decomposed organic fertilizer should be applied and phosphorus and potassium fertilizers increased. For the base fertilizer, change the previous band application to full-layer fertilization. Before winter, combined with digging and turning frozen soil for land preparation, apply 1500-2000 kg of decomposed chicken manure and 200-250 kg of decomposed cottonseed cake or rapeseed cake per mu, turning them into the lower layer; the upper-layer fertilizer is 50 kg of superphosphate and 50 kg of 45% potassium sulfate compound fertilizer (potassium chloride is taboo). After pollination of the second female flower, when the young fruit begins to swell, apply 20 kg of urea and 10 kg of potassium sulfate per mu at a distance of about 60 cm from the melon roots. During the young fruit swelling period, if continuous drought weather occurs, pay attention to appropriate watering or drip irrigation under the film for drought resistance. After the first batch of melons is harvested, apply 15 kg of urea + 10 kg of diammonium phosphate per mu under the plastic film on the inner side of the greenhouse frame as a relay fertilizer to promote the growth of the second and third batches of melons. IV. Scientific Pruning and Artificial Pollination  Small watermelons have weak early growth and small fruit type, so it is suitable to keep multiple vines and set multiple fruits. There are usually two pruning methods: first, the main-vine retention pruning method, that is, in addition to retaining the main vine, select and retain 2-3 strong secondary vines at the base, remove the remaining secondary and tertiary vines, and finally retain 3-4 vines for pruning; second, the pinching pruning method, pinch the main vine at the 5-6 true leaf stage, and after secondary vines emerge, keep 4-5 secondary vines of similar growth growing in parallel, and remove all other secondary or tertiary vines. Medium-fruit-type watermelons adopt the one-main-one-secondary double-vine pruning method. In order to improve the commercial rate and fruit-setting rate of watermelon, artificial pollination is usually carried out on the second female flower, and marking should be done at the same time. It is worth noting that for large-scale cultivation of Zaochun Hongyu watermelon, it should be interplanted with striped watermelon varieties of similar growth period that can provide sufficient pollen. After fruit setting, attention should be paid to fruit thinning; generally, keep 1 fruit per plant for the first batch of melons.

V. Regulating Temperature  According to the growth progress of watermelon and weather changes, timely remove and cover films to regulate the temperature in the greenhouse. 5-7 days after watermelon seedlings are transplanted, maintain a daytime temperature of 28-30°C and a nighttime temperature of 16-18°C; after seedling recovery, during the vegetative growth stage, maintain a daytime temperature of 26-28°C, and during the flowering and fruiting stage, 30-32°C; during fruit development and ripening, the minimum temperature is 20°C and the maximum should not exceed 35°C. It should be noted that when the outside temperature is above 25°C, the skirt film can be removed, but the top film of the greenhouse should not be removed, so as to avoid fruit cracking caused by continuous rainy weather. VI. Disease and Pest Control  Select disease-resistant varieties, pay attention to crop rotation or grafting to replace roots, and timely apply 50% carbendazim wettable powder 800-fold solution or 65% Baiduoke wettable powder 500-fold solution or 12.5% Zhiweiling 200-fold solution for root irrigation, which can effectively prevent Fusarium wilt. During the fruit-setting period of watermelon, especially when continuous rainy weather occurs in April, use 45% chlorothalonil smoke agent or 250 g of 15% procymidone smoke agent per mu for fumigation to control sclerotinia rot and gray mold; spray 75% chlorothalonil wettable powder 800-fold solution + 70% thiophanate-methyl wettable powder 800-fold solution to control phytophthora blight and anthracnose. Once aphids and tobacco whiteflies are found causing damage, use 70% Baogui (imidacloprid) wettable powder 5000-fold solution + 0.5% Chongman Like (abamectin) emulsifiable concentrate 1000-fold solution for spraying and killing. VII. Timely Harvesting  For spring cultivation of watermelon, the first batch of melons generally matures 32-35 days after pollination, and the second batch matures about 25 days after pollination. After picking, grade in time, attach trademarks, bag, package, and market.