Why are the blooms on my tomato plant dying and falling off?
"Blossom-Drop" is a condition suffered by tomatoes, peppers, snap beans, and some other fruiting vegetables where the plant blooms but fails to set fruit, the blooms die and fall off. It may be caused by the use of excess nitrogen fertilizers or dry windy conditions, but the most common cause is temperature extremes. Tomatoes, peppers and beans are especially picky about the air temps when it comes time to set fruit. If the night temps fall below 55 or rise above 75 or if the day temps are above 90, the pollen becomes tacky and non-viable. Pollination cannot occur. If the bloom isn't pollinated, the bloom dies and falls off.
Control: Water the plants deeply once a week, mulch heavily to maintain constant soil moisture levels, establish windbreaks as needed, avoid using excessive amounts of nitrogen fertilizers, and wait for temperatures to moderate and stabilize. Earlier timed planting can help attain fruit set prior to the on-set of high temps, and the use of protection can compensate for cool nights. Some recommend attempting hand-pollination with an artist brush or a gentle shaking of the plant/cage/support prior to the hottest part of the day will also help. Fruit set will resume when temperatures moderate. Hormone sprays, such as "Blossom Set", may prevent some blossom drop due to LOW temperatures. However, the resulting fruit are often misshapen. But studies prove that hormone sprays do not prevent blossom drop due to HIGH temperatures.