Troubleshooting tomatoes

Tomatoes not setting fruit this year? With the number inquires received lately at local ISU Extension Offices, this is a problem being experienced by many folks in our area. Although the most popular and easiest to grow vegetable; tomatoes are warm season plants, with pollination and fruit set being highly sensitive to temperature extremes.

Tomato blossoms are a complete flower, as they contain both male and female parts, and for the most part, are self-pollinated by wind. But when mid-morning temperatures reach 90 degrees and above, any tomato flowers which opened earlier that morning can abort and drop off the plant. Mid-July temperatures over 90 degrees also can inhibit the red color development of the fruit and those tomatoes will remain a yellow-orange color.

Cool nights can also interfere with tomato fruit set. If evening temperatures fall below 55 degrees, pollen will fail to develop in the tomato flower and any blossoms that open in the morning will not set fruit.

Soils low in nitrogen will produce tomato plants with weak vines that cannot support a crop. However, do not over-apply fertilizer, as too much fertilizer high in nitrogen can cause blossom drop, with plants producing excessive foliage, rather than setting fruit.

Other potential causes of tomato blossom drop include fluctuation in soil moisture, so keep roots uniformly moist throughout the growing season. Excessive wind can knock blossoms off the plant. Low light levels also may be a cause, as tomatoes need 6 to 8 hours of sunlight to do well. Insect damage to the plant or disease also can have a negative effect on tomato fruit set.

Eggplant and peppers are both warm season plants that can also experience low fruit set. Remember to use mulch around your plants to help provide best possible growing conditions.

Did you know? For best eating quality and texture, store tomatoes at room temperature, not in the refrigerator. And for optimal flavor, allow tomatoes to become fully ripe on the vine and harvest before they begin to soften.

Want to learn more about horticulture through training and volunteer work with the ISU Master Gardener program? Contact Yvonne McCormick at for further information.