To modernize the traditional method of bitter gourd cultivation, it's essential to select varieties that are resistant to cold and not overly sensitive to high temperatures, which can pose challenges in winter greenhouse production. In recent years, some regions have successfully adopted grafting techniques to grow bitter gourd in solar greenhouses. This method enhances disease resistance, ensures safe growth during winter, and allows for earlier harvests. The yield per acre can reach around 3,000 kilograms, leading to higher economic returns. Below are the detailed cultivation techniques.
The Blue Mountain Bitter Gourd variety was chosen, and black-seeded pumpkin was used as a rootstock due to its good compatibility, strong cold tolerance, and high yield.
**1. Seed Treatment:**
Bitter gourd seeds were sown in early October. They were soaked in 50–55°C hot water for 15–20 minutes while continuously stirring and adding hot water to maintain the temperature. After cooling to room temperature, they were soaked for 12 hours. Germination occurred at 30–35°C. Pumpkin seeds were soaked for 6–8 hours and germinated at 25–30°C. The pumpkin was sown one or two days later, with most seeds sown when exposed. When the pumpkin had developed true leaves, it was time to graft the bitter gourd.
**2. Grafting Method:**
Grafting should be done using the planting method. Immediately after grafting, the small arch cover is placed over the plants, and the temperature is raised to 30–32°C during the day and about 20°C at night, with humidity above 95%. For the first three days, shading is required all day, except on cloudy days. From day 3 to 6, shading is applied from 10:00 AM to 3:00 PM, and light is allowed otherwise. Survival typically occurs within 10 days, after which the roots are cut. The temperature is then maintained at 25°C during the day and 15°C at night. Before planting, the nighttime temperature can be reduced to about 10°C for low-temperature hardening. Planting usually takes place in early December.
**Soil Preparation and Planting:**
Before planting, deep soil preparation is carried out. Per acre, 10,000 kg of high-quality organic fertilizer, 100–150 kg of cooked cake, and 25 kg of diammonium are applied. The plant spacing is 80 cm between rows and 30 cm between plants, totaling 2,800 plants per acre. Mulching is also used to cover the planting area.
**Temperature Management:**
After planting, it’s crucial to keep the greenhouse closed to raise the temperature and promote seedling growth. During sunny days, the temperature can reach 30–35°C, and at night, it should not drop below 12–15°C. Once the seedlings are established, the temperature is gradually lowered to normal levels—daytime 20–25°C and nighttime 15°C. These principles are similar to those used for cucumbers.
**Fertilizer and Water Management:**
Once the seedlings are stable, watering is done along the ditches. During the winter and spring, 1–2 times of irrigation are carried out. After the seedlings recover, a single irrigation is done, followed by a period of warming to promote root development. Fertilization is controlled before this stage to ensure steady growth. The first fertilizer application occurs after the male flowers open, followed by another application after fruiting, with increasing amounts of water and fertilizer. Watering is done every 3–4 days, and fertilizing every 7–8 days. A total of 15–20 kg of compound fertilizer is used per acre. When the weather warms up in spring, 2–3 times of flushing with human excrement is done, using 1000–1500 kg per acre.
**Vine Training and Plant Adjustment:**
When the vines reach about 30 cm, trellises are inserted to guide the vines upward. Vines are trained in an S-shaped manner. The main vine is dominant, and side branches below 50 cm from the ground should be removed promptly. If side branches become too dense, they should be pruned. Ensuring the main vine grows strongly is key. Once the main vine reaches the top of the trellis, it is pinched back. 3–5 side vines are left at the lower part, with 1–2 fruits per side. Some growers also take two strong side vines when the main vine is about 1 meter long. Tendrils and male flowers must be removed during vine training. Vines should be adjusted for direction and position, and old, weak, or dense vines should be cut to reduce shading.
**Pollination and Harvesting:**
Male flowers that open on the second day in the afternoon are collected and kept in a dry environment at around 25°C. On the next morning, the male flowers are gently opened, and the stigma is pollinated. One male flower can pollinate 3 female flowers without damaging the stigma. Bitter gourd is harvested when the fruit is tender, typically 12–15 days after flowering. The fruit should have swollen strips and knobs, a smooth and shiny top, and a bright green, glossy skin.
**Pest and Disease Control:**
Prevention and control should follow the principle of “prevention first, comprehensive measures, accurate diagnosis, and targeted treatment.†Common diseases include fusarium wilt, bacterial blight, downy mildew, and pests like fruit flies and aphids.
- **Fusarium Wilt:** Symptoms include wilting at the base, with vascular browning. Prevention includes avoiding continuous cropping, using healthy seedlings, and applying seed coating agents like “2.5% Shiloji†suspension.
- **Bacterial Blight:** Leaves show water-soaked spots and V-shaped lesions. Treatments include using bactericides like “Shigao†at 1000–1500 times dilution.
- **Downy Mildew:** Causes yellowing and brown spots on leaves. Prevention involves proper drainage, adequate fertilization, and using fungicides like “Jin Lei Duo Mier.â€
- **Fruit Fly:** Adults lay eggs in fruits, causing rot. Control methods include trapping with yellow boards, insecticide spraying (e.g., “Kung Fuâ€), and bagging fruits.
- **Aphids:** Suck sap from young shoots, causing curling and yellowing. Use 25% Aktai water dispersible granules at 5000–10000 times dilution.
- **Thrips:** Feed on leaves, causing damage. Use 50% Coulomb at 1000 times or 2.5% Kung Fu at 1500 times.
By implementing these advanced techniques, farmers can significantly improve the quality, yield, and profitability of bitter gourd cultivation in greenhouses.
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