At this point in the growing season many tomato plants have started dropping flowers and not producing fruit. Before removing these plants from the vegetable garden, read this!
Blossom drop can be due to a lack of pollination. Tomato plants have complete flowers, meaning they contain both male and female parts within the same flower. The tomato flowers hang down in a cluster and are pollinated when shaken by movement such as wind. Insects are not necessary for tomato flowers to be pollinated. When the flowers are not properly pollinated, they die and drop off the plant.
Many factors can affect pollination. At this time of the year high temperatures or drought are usually the reason for blossom drop. The optimum daytime growing temperature range for tomatoes is between 70 and 85 F. Several days of nighttime temperatures above 70 F and or daytime temperatures above 85 F will cause the plants to abort flowers. Under these temperatures the pollen becomes tacky and nonviable, preventing proper pollination from taking place. When this happens, the flowers dry up and fall off. When temperatures get this high the best thing a gardener can do is keep the plants irrigated and wait for more favorable growing temperatures to arrive. NOTE: The same problem occurs when temperatures are too low. Nighttime temperatures below 55 F will prevent pollination from occurring as well. For more information on growing tomatoes see HGIC 1323, Tomato.