Unpollinated tomato blooms start to shrivel and fall from the plant.
A lot of questions and calls come in every year about tomato plants not setting fruit. They look great and flower, but nothing happens beyond that. Unfortunately, the problem is usually not a disease or an insect — those can be controlled. This particular issue can be blamed on Mother Nature.
Here's a brief horticultural lesson
Tomatoes are self-pollinating, meaning they have flowers that contain both the male and female parts, so more than one plant is not needed for reproduction. The pollen falls within the flower to pollinate itself. That doesn't mean insects and wind aren't important, though. They can help pollinate self-pollinating plants; for example, when bees light on the yellow flowers, the buzzing of their wings helps to shake the pollen off into the flower.
All of this can be perfect and you might still be faced with tomato plants not setting fruit. Here's why: high temperatures.
When temperatures rise above 85 to 90 degrees F (depending on humidity) during the day and 75 degrees F at night, pollen will become unviable. Humidity can also come into play. In the extreme humid regions of the U.S., pollen may become so sticky that it does not fall. On the other end of the spectrum, in the arid regions, pollen may become so dry that it does not stick to the female part of the flower. Many gardeners try to gently shake the plant to encourage pollination, but a lot of times it is just not going to work.
If you're faced with tomato plants not setting fruit, the best thing to do is to keep the plants healthy and fertilized with plant food, such as Miracle-Gro® Shake ‘n Feed® Tomato, Fruit & Vegetable Plant Food. The plants will start to produce again when the weather becomes favorable. Note, though, that heirloom tomatoes can be even fussier about temperatures than most hybrid tomatoes, and in some areas will wait until late summer or early fall to start setting fruit.
There are tomato varieties that will set more fruit than most in the heat (although extreme heat will inhibit most all of these plants from setting fruit). Heatmaster and Solar Fire are two of these varieties. For more, check out the full range of Bonnie Plants' heat tolerant tomato varieties. Also be sure to consult our tomatoes page for more info on planting, growing, and caring for tomato plants.
If you're still stumped about why your tomato plants won't set fruit — or have another question about growing tomatoes — visit our Ask an Expert page. Happy growing!