Growing Watermelon

Watermelons (Citrullus lanatus) are a delightful addition to gardens in Missouri’s Zone 6b-7a, offering refreshing fruit during the hot summer months. To ensure a successful watermelon harvest, consider the following guidelines:

1. Choosing the Right Variety
   • Recommended Varieties for Missouri:
     • Seedless Varieties: ‘Vanessa Mini Seedless’ produces small, sweet fruits with dark rinds. 
     • Seeded Varieties: ‘Allsweet’ and ‘Crimson Sweet’ are popular choices known for their flavor and size.
   • Considerations:
     • Seedless watermelons require specific pollination conditions; planting both seedless and seeded varieties together can improve fruit set.
     • Choose varieties with resistance to common diseases like Fusarium wilt and powdery mildew.
2. Planting Time
   • Indoor Sowing:
     • Start seeds indoors 4-6 weeks before the last expected frost, typically in late March to early April.
   • Transplanting Outdoors:
     • After the last frost date, when soil temperatures reach 70°F (21°C), usually mid-May in Missouri.
   • Direct Sowing:
     • Not recommended; transplanting provides better control over growth conditions.
   • Regional Planting Dates:
     • North Missouri: Mid-May to early June.
     • Central Missouri: Early to mid-May.
     • South Missouri: Late April to early May.
   • extension.missouri.edu
3. Site Selection & Soil Preparation
   • Sunlight Requirements:
     • Full sun exposure (8-10 hours daily) is optimal for vigorous growth and fruit production.
   • Soil Requirements:
     • Well-drained, sandy loam with a pH of 6.0 to 6.8.
     • Incorporate organic matter to enhance fertility and soil structure.
   • Soil Testing:
     • Conduct a soil test to determine nutrient levels and amend soil accordingly.
   • extension.missouri.edu
4. Planting Instructions
   • Spacing:
     • Space plants 36-42 inches apart in rows, with rows 6-8 feet apart to accommodate vine growth.
   • How to Plant:
     • Create mounds or hills 4-6 feet apart, each with a diameter of 12-18 inches.
     • Plant 4-5 seeds per mound, covering with 1 inch of soil.
     • Thin to the 2-3 healthiest plants per mound after germination.
   • extension.missouri.edu
5. Watering & Maintenance
   • Watering Needs:
     • Maintain consistent soil moisture, especially during flowering and fruit development.
     • Drip irrigation is recommended to keep foliage dry and reduce disease risk.
   • Fertilization:
     • Apply a balanced fertilizer at planting and side-dress with nitrogen during vine growth.
   • Mulching:
     • Use mulch to conserve moisture, suppress weeds, and prevent soil-borne diseases from splashing onto plants.
6. Companion Planting Benefits
   • Good Companions:
     • Corn and peas can provide natural support and shade, benefiting watermelon vines.
   • Avoid Planting Near:
     • Potatoes and other nightshades, as they share common pests and diseases.
7. Pests & Diseases
   • Common Pests:
     • Cucumber Beetles: Can transmit bacterial wilt; use insect exclusion screens and monitor with yellow sticky traps. extension.missouri.edu
     • Squash Bugs: Remove by hand or use appropriate insecticides.
   • Common Diseases:
     • Powdery Mildew: Ensure proper spacing for air circulation and apply fungicides as needed.
     • Fusarium Wilt: Rotate crops and select resistant varieties.
8. Harvesting & Uses
   • Harvesting:
     • Fruits are ready when the underside turns from white to yellow, and the tendril nearest the fruit dries.
     • A hollow sound when tapped also indicates ripeness.
   • Uses:
     • Enjoy fresh, in salads, or as juice.
     • Store in a cool, dry place; harvested fruits can last several weeks.
9. Winter Protection & Overwintering
   • Watermelon vines are annuals and do not survive Missouri winters.
   • Seed Saving:
     • Collect seeds from mature fruits before the first frost.
     • Clean, dry, and store in a cool, dry place for planting the following season.
10. Missouri-Specific Considerations
    • Heat Tolerance:
      • Watermelons thrive in heat but may require afternoon shade during extreme heat waves.
    • Humidity & Disease Risk:
      • High humidity can promote fungal diseases; ensure proper spacing and airflow.
    • High Tunnel Production:
      • Using high tunnels can extend the growing season and protect fruits from pests. 
11. Summary of Key Tips
    • Start seeds indoors in late March to early April.