A lot of questions and calls come in every year about tomatoes that look great and flower, but do not set a lot of fruit. Unfortunately, it is not a disease or an insect—those can be controlled. You can blame this problem on Mother Nature.
First, 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 the flower can still fail to set fruit. High temperatures are the main culprit.
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 have this problem, the best thing to do is to keep the plant healthy and fertilized. Try Bonnie Plants Herb & Vegetable Plant Food. The plant will start to produce again when the weather becomes favorable. 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). Talladega and Solar Fire are two of these varieties. For more heat-setting varieties, check out Bonnie Plants heat tolerant tomato varieties. Also be sure to consult our Bonnie Plants Learn & Grow Library if you have other questions about growing tomatoes.
If you’re still stumped, send your question in through our Ask an Expert page.