Watermelons thrive in warm, dry, and sunny conditions. The ideal temperature for seedlings is 20-25°C, while flowering and pollination require around 25°C. During fruit development, temperatures should be below 30°C, with nighttime temperatures not dropping below 22°C. Watermelons are not frost-resistant and grow poorly at low temperatures. They also struggle in overly wet or dry conditions, and cloudy or rainy weather can negatively affect pollination. Therefore, it's best to avoid planting during cold or rainy seasons. Watermelons prefer well-drained sandy loam soil rich in organic matter with a pH between 5.0 and 7.0.
Cultivation techniques:
1. **Planting Period**: In southern China, sowing typically occurs from December to early February in spring and July to early September in autumn. For other regions, adjust based on local climate conditions.
2. **Seed Soaking and Germination**: Soak seeds for 6–8 hours, depending on the temperature. After soaking, wash the seeds thoroughly to remove any sticky residue. Dry them slightly so they don’t stick together. Wrap the seeds in a damp cloth and place them in a constant temperature of 28–30°C for 24–30 hours to promote germination.
3. **Sowing**: To ensure good germination and ease of management, use seedling trays filled with loose, nutrient-rich media. Soak the seedlings in water for 1–2 hours before sowing, and plant the seeds when the sprout is about 0.2 cm long. Place the seed with the bud facing down at a depth of approximately 0.4 cm.
4. **Seedling Management**: Once the seedlings emerge, gently remove the seed coat to prevent it from restricting light to the cotyledons. Maintain a temperature of 20–25°C, keep humidity moderate, and ensure good ventilation and light to prevent diseases.
5. **Land Preparation**:
- Choose a flat area with good drainage and access to irrigation.
- In southern China, use a deep trench system (3–4 meters wide) with spacing of 0.7–1.2 meters.
- Apply base fertilizer: 50 kg/mu of phosphate and 50 kg of compound fertilizer. Apply two rounds of fertilizer—first near the plants, then further away as the fruit develops.
- Use silver-black plastic mulch to suppress weeds, retain moisture, and reduce pests like aphids.
- Transplant seedlings when they have two true leaves, typically 25 days after sowing in spring and 12 days in autumn.
6. **Fertilizer Management**:
- 10 days after planting, apply a 0.3–0.5% urea solution to promote growth.
- Use a small amount of ternary compound fertilizer with irrigation to encourage vine growth, but avoid excessive nitrogen to prevent legginess.
- During flowering, control water and apply high-phosphorus, high-potassium foliar fertilizer to support female flower development.
- When fruits begin to grow, increase phosphorus and potassium application and ensure adequate watering.
7. **Pruning and Fruit Thinning**:
- Prune based on variety, climate, and spacing. A common method is to leave one main vine and two strong side vines.
- For smaller varieties, allow fruit to develop after the second female flower, but avoid over-thinning to prevent deformation.
8. **Pest and Disease Control**:
- **Seedling Blight**: Caused by high humidity and heat. Symptoms include water-soaked lesions and white mold. Treat with fungicides like Ridomil or Kocide.
- **Anthracnose**: Appears in hot, rainy weather. Early signs include yellow spots that turn into concentric rings. Prevent with copper-based sprays.
- **Downy Mildew**: Thrives in cool, humid conditions. Yellow spots appear on the underside of leaves. Use mancozeb or dimethomorph for prevention.
- **Fusarium Wilt**: Affects plants in continuous cropping areas. Symptoms include wilting and brown vascular tissue. Rotate crops and use resistant varieties.
- **Broom Disease**: Causes yellow, oily lesions and jelly-like exudates. Treat with copper or thiophanate-methyl.
- **Deformed Fruits**: Caused by low temperatures, poor pollination, or nutrient imbalances. Improve lighting, use compost, and perform artificial pollination.
Harvesting Tips:
1. **Estimate Harvest Time**: Small watermelons take about 35 days to mature, and this may be adjusted based on the season.
2. **Listen to the Sound**: Tap the middle of the melon. A hollow sound indicates maturity.
3. **Check the Stripe and Color**: Mature watermelons have distinct stripes and a bright green color.
4. **Look for Yellow Hairs**: A yellow, curly hair near the stem is a sign of ripeness.
If you have any questions or need further assistance, feel free to contact us directly. We're here to help you grow the best watermelons!
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