This is why your Fruit Set Fails

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This is why your Fruit Set Fails

Fruit development begins with fruit set and ends with maturity. While this stage can last anywhere from 1 to 7 months depending on species, many factors contribute to the success or failure of this stage and therefore determine the outcome of the season. Fruit set is a transition phase of the ovary from the flower to the developing fruit, and takes place a few days after the floral opening. The ovary begins its development after pollination and fertilization or, in its absence, through parthenocarpy.

In the case of tomatoes, flower buds can form under different environmental conditions. However, for fruit set to take place successfully, special conditions are to be met. In the absence of the latter, flowers are lost shortly after they open.

Nutritional Balance

Fruit-bearing depends on the accumulation of new quantities of carbohydrates that exceed the need for vegetative growth. The concentration of carbohydrates in the plant depends on the balance between their manufacture and use in breathing and in building new tissues.

Water Balance

Flowers fall in the event of exposure to dry winds with low relative humidity and a lack of ground moisture, as the continued lack of soil moisture leads to the petals becoming pale yellow and the flowers falling without setting.

Temperature and Light Intensity

High and low temperatures have a bad effect on the fruit set. The appropriate thermal range is between 15-22 degrees Celsius, as fruit set decreases significantly if the temperature at night drops to 13 degrees, and increases during the day to more than 32 degrees.

Intense lighting increases the harmful effects of high temperatures on the fruit set process. In this context, high temperatures cause:

  • Decreased level of carbohydrates and their inefficient transfer within the plant.
  • Lack of pollen production and disruption of the process of their formation.
  • Poor vitality and germination of pollen.
  • Protrusion from the obturator tube.
  • Drying up and browning of stigmas.

Therefore, if you are in a region with high temperatures in the summer, you should choose varieties that are tolerant of high temperatures, otherwise, fruit set will fail and production will decrease.


One of the complications affecting the quality of the pollination of tomatoes is the high or low air humidity. Too high a humidity can cling pollen to the flower, so it is unable to fall off and pollinate while in very dry climates the flowers may become so dry that the pollen doesn’t stick and roll right off it. In this case, regular watering may help raise the humidity around the plants enough to improve conditions and pollination.


The first thing to consider to get a good crop is how easily pollinating insects can get to your tomato flowers. Although tomato flowers are self-fertilizing, meaning that each flower can pollinate itself, the presence of bees and/or wind greatly improves pollination by pushing the flowers just enough to help dislodge pollen from the stamens and into the pistils themselves or other flowers. Hence, a very large percentage of farms in many countries depend on bumblebees to pollinate flowers and to ensure a good yield of quantity and quality, as the bees shake the flowers to pollinate them. You can artificially pollinate tomato flowers by gently shaking the plants (by hand or with a vibrator) to mimic the hum of bees for pollination.

Genetic Structure of the Variety

Genetic Structure has a major role in the process of setting fruits, as the tomato variety SV 8320, for example, which bears environmental stresses and gives a successful crop and high yield in addition to yielding solid fruits that are tolerant to shipping and with high quality specifications. Therefore we direct its cultivation at the beginning of May to give good fruits in periods of extreme heat during the month of August.

Maryse Bou Zeid

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