Temperature Concerns

• Watermelons cannot tolerate frost and develop slowly in cool temperatures. Plant the melons outside only after spring frost danger has passed and after daytime temperatures rise above 70 degrees Fahrenheit. In areas with short summer growing seasons, cover the bed with black plastic mulch. The mulch helps the soil warm earlier and traps in the heat during short periods of cooler temperatures. Keeping the soil constantly warm improves the chances that the watermelons develop well and quickly.
  
  

Pollination Problems

• Seedless watermelon varieties are sterile, so the plants cannot inter-pollinate with themselves. This inability to pollinate results in no fruit development unless you provide a pollinator. Plant some seeded watermelon varieties interspersed with the seedless types. The seeded varieties will pollinate the seedless melons, which results in the development of seedless watermelons. Choose a seeded variety that looks different than the seedless variety or mark the plants well so you can determine which melons are seedless and which aren't when harvesting.
  
  

Water Stress

• The deep roots of watermelons help them survive dry weather periods, but they still require some irrigation to fruit well. Using a plastic mulch helps conserve soil moisture and minimizes the irrigation needs of the plants. Water the melons during extended drought periods, providing approximately 1 inch of water weekly, so the soil doesn't dry out completely. Over-watering can also result in poor fruit development as the plants are more prone to root rots and fungal diseases in soggy soil.
  
  

Pests

• Severe insect infestations can stunt the growth of the plants or cause fruits to develop poorly. The prime pest of watermelons is the cucumber beetle. The beetles feed on the watermelon foliage. The damaged foliage cannot absorb sunlight efficiently, which results in poor growth and development. Fungal diseases can also attack watermelons and cause poor growth. Planting disease-resistant watermelon varieties helps alleviate disease concerns.