Tomato plants produce yellow flowers, which are the precursors to the fruit. The appearance of these blooms signals that the plant is moving from its vegetative growth stage to its reproductive stage. The successful transition of these blooms is a direct measure of the plant’s eventual yield.
The Anatomy of the Tomato Flower
The yellow color of the tomato flower is typical of the Solanum family, which includes potatoes and eggplants. Tomato plants produce a “perfect flower,” meaning each bloom contains both male and female reproductive organs. The flower typically has five to nine pointed petals surrounding the central structures.
The male parts (stamens) are fused together, forming a hollow, yellow cone that encloses the female part (pistil). This compact structure adapts the tomato flower for self-pollination. The pistil, consisting of the stigma, style, and ovary, is protected within the stamen cone.
How Tomato Flowers Become Fruit
The tomato flower is primarily self-pollinating, meaning pollen from the stamen can fertilize the pistil of the same flower. For this process to occur, pollen must be released from the anthers and transferred to the stigma. Because the pollen is relatively heavy and sticky, mechanical disturbance is necessary to shake it loose within the flower’s cone.
Outdoors, this vibration is provided by wind or by insects like bumblebees, which use “buzz pollination” to dislodge the pollen. Once the pollen lands on the stigma, it grows a tube down to the ovary, where fertilization takes place. The ovary then swells and develops into the tomato fruit, becoming visible within 24 to 48 hours.
Successful fertilization depends on environmental conditions that support pollen viability and movement. The ideal daytime temperature for fruit set ranges between 70°F and 85°F, with nighttime temperatures between 55°F and 70°F. Optimal relative humidity is 40 to 70%, as extremes can cause pollen to become too dry or too wet to shed properly.
Why Flowers May Not Set Fruit
A common issue is “blossom drop,” which occurs when yellow flowers dry up and fall off without setting fruit. This failure is the plant’s response to stress, indicating unsuitable conditions for reproduction. Temperature extremes are a frequent cause, as high temperatures exceeding 90°F can sterilize the pollen, while prolonged nighttime temperatures below 55°F interfere with fertilization.
Humidity that is too low or too high also inhibits pollination. Low humidity dries out the pollen, making it non-viable, while high humidity causes the pollen grains to clump together. Another factor is a nutrient imbalance, particularly excess nitrogen, which encourages foliage growth over flower production, leading to aborted blooms.