Why Tomatoes Bloom but There Is No Fruit

Pollination

• Tomato blossoms are self-fertile, which means that each flower has both male and female reproductive parts. Gentle winds that shake the plants and beating bee's wings that vibrate the flowers ordinarily provide the plant with enough stimulation for fertilization. In conditions where there is no wind, such as those found in a greenhouse or sheltered location, and when bees don't visit the garden, flowers can't fertilize themselves and drop from the plant without producing fruit. Giving the plant a gentle shake every two or three days improves the pollination.

Temperature

• Tomato plants set fruit when daytime temperatures are below 85 degrees F and nighttime temperatures are between 55 and 70 degrees F. They tolerate temperatures outside these ranges for a few days, but when unfavorable conditions persist they switch their focus from procreation to survival and drop their flowers. Tomato varieties labeled as heat set, heat tolerant or hot set tolerate high temperatures without dropping their flowers. These varieties are ideal for southern climates where temperatures soar early in the season. Heat-set varieties include "Sun Leaper", "Suncrest", "Mountain Crest", "Sunbeam" and "Sunmaster." Cherry types that set fruit during periods of high temperatures include "Legend," "Gold Nugget," "Oregon Star" and "Oregon Spring."

Humidity

• When humidity is high, the pollen sticks to the stamen, or male part of the flower. Since it can't drop onto the pistil, or female part, no fertilization takes place and the flower falls from the plant without producing fruit. When humidity is too low, the pollen loses all of its stickiness so that when it drops it can't adhere to the pistil. The ideal range for humidity 40 to 70 percent. In cases of low humidity, spray the flowers with water during the day to improve the chances of fertilization.

Other Causes

• Several other factors may prevent tomato plants from producing fruit. Tomato plants that receive less than six hours of sunlight per day are unlikely to produce fruit. Shallow watering causes stress that may prevent plants from blooming, and too much water or nitrogen fertilizer results in lush foliage at the expense of blossoms. Plants that don't get enough nitrogen are weak, spindly and unable to support a crop.