Tomato flowers are the necessary starting point for the fruit. The transformation process involves successful fertilization, leading to what is known as fruit set. Tomatoes are largely self-pollinating, as a single flower contains both the male and female reproductive parts required for this process. Successful fruit set depends entirely on effective pollination under favorable conditions.
The Journey from Flower to Fruit Set
The tomato plant produces a “perfect” flower, containing both the male stamens and the female pistil within the same structure. The male parts, called anthers, are fused into a cone surrounding the female stigma and style. This arrangement facilitates self-pollination, requiring only a short transfer distance for the pollen.
For pollination to occur, the pollen must be dislodged from the anther cone and fall onto the receptive stigma. Since tomato pollen is heavy and sticky, this transfer requires mechanical vibration, usually provided by wind or the “buzzing” action of certain bees. Once on the stigma, the pollen germinates and grows a tube into the ovary, where fertilization of the ovules occurs.
Fertilization triggers hormonal changes within the flower’s ovary. Plant hormones, such as auxin, initiate cell division and expansion in the ovary tissue. The ovary begins to swell and enlarge, developing into the fleshy fruit we recognize as a tomato. Since the fruit develops from the flower’s matured ovary, the tomato is technically defined as a berry.
Why Tomato Flowers Sometimes Fail to Produce Fruit
When tomato flowers shrivel and drop off, known as “blossom drop,” it indicates a failure in the fertilization process. This failure is often caused by environmental stress that makes the pollen nonviable or interferes with its transfer. Temperature extremes are a frequent culprit; pollen can become sterile when daytime temperatures exceed 90°F (32°C) or when nighttime temperatures drop below 55°F (13°C).
Humidity levels also affect successful pollination. If the air is too humid, the pollen becomes sticky and clumps together, preventing it from shaking loose from the anthers. Conversely, very low humidity can dry out the pollen or the stigma, inhibiting adherence. In either case, pollen transfer is inhibited, and the flower is aborted.
Nutrient imbalances, particularly an excess of nitrogen, can also lead to failure. High-nitrogen fertilizers encourage the plant to produce lush foliage at the expense of flower and fruit development. Another element is insufficient mechanical vibration from wind or insects, which results in poor pollination because the heavy pollen remains trapped within the anther cone. Without this aid, the self-pollination process cannot be completed, and the flower withers.
Practical Steps for Ensuring a Good Harvest
Gardeners can take proactive steps to mitigate environmental stresses and encourage successful fruit set. Managing the temperature and humidity around the plants, especially in protected spaces like greenhouses, is important. Ensuring good air circulation by opening vents or using fans prevents pollen from becoming too sticky in high humidity.
When natural vibration is lacking, such as in calm or indoor growing conditions, manual assistance is required. You can mimic wind or bees by gently tapping or shaking the flower clusters once a day during midday hours. Using an electric toothbrush to briefly vibrate the base of the flower cluster provides effective “buzz pollination” that maximizes pollen release.
Consistent water management is also necessary, as inconsistent watering stresses the plant and contributes to flower drop. Aim for steady soil moisture, avoid overwatering, and consider using mulch to regulate soil temperature and retain moisture. Once the plants begin to flower, switch from high-nitrogen feeds to fertilizers higher in phosphorus and potassium to support fruit development.