Improper Nutrition

• Although tomatoes are easy to grow, a nutrition imbalance makes it difficult for tomatoes to produce fruit. Nitrogen is usually the nutrient in question. An inadequate supply of nitrogen makes it difficult for tomatoes to produce, but an oversupply of nitrogen creates the same problem. Fertilizers not formulated specifically for tomatoes can provide too much nitrogen for tomato plants.
  
  

Inclement Weather

• Conditions, such as temperature and humidity, make it difficult for tomato fruit to set. High humidity prevents pollen from fertilizing the flower properly. Tomatoes have a difficult time producing fruit when overnight temperatures remain above 70 degrees F, or when daytime temperatures are consistently above 90 degrees F. Temperatures below 60 degrees F during the day are also detrimental to fruit production.
  
  

Insufficient Light

• Tomato plants thrive on direct sunlight and need at least eight hours of direct sunlight daily to produce a good crop. If your plants are in the shade for more than three hours a day, especially in the afternoon, your tomato plants may have trouble setting fruit. If you live in an area where temperatures regularly rise above 90 degrees F during the summer, provide some shade or select more heat-resistant tomato varieties.
  
  

Other Potential Explanations

• Tomato flowers exposed to consistently windy conditions die before they set fruit, since the wind can makes it difficult for the pollen to adhere and fertilize the flower. Insect problems, most commonly aphids or thrips, also distress the tomato plant enough that it will not set fruit. An inconsistent water supply inhibits proper fruit production on tomato plants.