Tomato fruit production starts with successful pollination—the transfer of pollen. Tomato flowers are “perfect,” containing both male anther and female pistil reproductive parts, but still require movement (like wind or vibration) for pollen transfer to the stigma. Identifying successful fertilization is the first step in knowing if a fruit will develop. Successful pollination causes the plant to direct energy into the flower’s base, initiating visible structural changes.
Observing Changes in the Flower Structure
The first signs of successful fruit set appear in the flower’s outer layers (the corolla and stamen) within 24 to 48 hours of pollination. The bright yellow petals (the corolla) quickly wilt, shrivel, and curl inward. This rapid wilting signals that the plant has transitioned from flower display to fruit production.
The central reproductive structure also changes immediately; the stigma and anthers often darken and shrivel slightly. Within two or three days, the entire spent flower structure, including the wilted petals, dries up and falls away from the stem. This shedding confirms that fertilization is complete and the plant is preparing to nurture the developing fruit.
Monitoring the Ovary and Calyx
The definitive confirmation of successful pollination is “fruit set,” the visible start of a tiny tomato forming. The ovary, a small, green, bulbous structure behind the petals, is the part that swells and enlarges. After successful pollination, the ovary transforms, visibly growing into a miniature green sphere, sometimes felt as a BB-sized bump days after the petals drop.
The calyx, the small, star-shaped cluster of green sepals at the flower’s base, remains firmly attached to the stem. As the fruit grows, the calyx points backward, or reflexes, away from the emerging tomato. This combination of a rapidly swelling green ovary and a persistent green calyx is the clearest visual evidence of the transition from flower to fruit.
Recognizing Failed Pollination and Blossom Drop
If pollination or fertilization fails, the plant will not invest energy into the flower, resulting in “blossom drop.” This is identified when the entire flower, including the stem (pedicel), turns yellow before detaching and falling off the plant. The lack of a hormonal signal causes the plant to abort the flower, conserving resources for other blooms.
Blossom drop often signals environmental stress interfering with the reproductive process. Extreme temperatures are common causes; pollen becomes nonviable when daytime temperatures exceed 90°F or nighttime temperatures fall below 55°F. High humidity can cause pollen to clump, while low humidity can cause it to dry out, both preventing successful pollen transfer.