Now that your tomatoes are bursting with growth and flowers and you are waiting for the fruit to ripen, you find flowers dropping or withering on the plant. Why is that happening? The problem is called blossom drop. The main reason is that the flowers are not getting pollinated. Tomatoes have perfect flowers, meaning both male and female flower parts are in the same flower. The pollen is moved from the male part (stamen) to the female part (pistil) by wind movement of the plant or by vibration of the flower by bumble bees or other pollinators.
So what are the causes of lack of pollination?
One of the main causes is from daytime temperatures exceeding 85°F or nighttime temps rising above 70°F or dropping below 55°F. You can put up some shade cloth (30% should be enough) over your tomatoes, positioned so it is shading your plants during the hottest time of the day. To learn more about other causes of flower drop, you can read the blog Why are My Tomato Flowers Falling Off and Not Making Fruit?