The blossoms on your tomatoes are not pollinating for some reason, there are a variety of things that can cause this. Temperature can be a contributing factor, extreme temperatures can cause the blossoms to drop. Make sure that you plant tomatoes that are developed to tolerate hot weather. Humidity can also affect pollination. During real high temperatures and low humidity, it's a good idea to water the actual plant during the afternoon or evening. You need to thoroughly water every 3-4 days to promote root growth soak soil 3-4 feet around plant. Please call me at (254) 559-2313 for additional information and a brochure on tomato gardening.