Pollination is the transfer of pollen, which contains the male reproductive cells, from the anther to the stigma, the receptive female part of a flower. For tomato plants, this process is generally straightforward because the flowers possess all the necessary components for reproduction within a single bloom. Tomatoes are categorized as self-fertile, meaning a single plant can produce fruit without needing pollen from a separate plant.
The Anatomy of the Tomato Flower
Tomato plants produce “perfect” flowers, meaning each yellow blossom contains both the male and female reproductive structures. The female part, the pistil, is centrally located and consists of the stigma, style, and ovary. Surrounding the pistil are the male parts, the stamens, which produce the pollen.
The arrangement of these structures is specifically adapted for self-pollination. The stamens are fused together along their edges, forming a hollow, column-like structure called the anther cone. This cone completely encloses the stigma and style of the female pistil.
This physical configuration ensures that the pollen, once released, remains confined within the flower and in extremely close proximity to the stigma. The style, which connects the stigma to the ovary, is often short enough to keep the stigma safely tucked inside the anther cone.
Natural Pollination Mechanisms
Although the tomato flower is designed for self-pollination, the process is not entirely passive; it requires physical agitation. Tomato pollen grains are relatively heavy and dry, held tightly within the anther cone. The pollen is released through small pores or slits at the tip of the anthers, similar to powder in a salt shaker.
The pollen must be physically shaken out of the anther cone to fall onto the stigma below, a process called sonication or “buzz pollination.” In nature, this vibration is provided most effectively by certain insect species, particularly bumblebees. Bumblebees grasp the flower and vibrate their flight muscles at a high frequency, causing the entire flower to shake and dislodge the pollen.
In outdoor garden settings, wind vibration is the most common natural mechanism that mimics the bee’s buzzing action. A moderate breeze is often enough to shake the flowers and release the pollen onto the stigma, successfully initiating fruit set. The more intense vibration from a buzz-pollinating insect generally results in more complete pollination, leading to larger and better-formed fruit. Cross-pollination between different tomato varieties is rare.
Manual Intervention for Successful Fruit Set
When tomato plants are grown in controlled environments, such as greenhouses, or in outdoor areas with very still air, the natural agitation needed for pollen release is absent. In these situations, human intervention is necessary to ensure successful fruit production by replicating the required vibration.
A simple and effective technique is to gently shake the entire plant or tap the flower clusters with a finger. This should be done during the optimal time for pollen release, typically midday when temperatures are warm and humidity is lower. Ideal conditions for pollen viability and transfer are daytime temperatures between 70 and 85 degrees Fahrenheit.
A more precise method involves using an inexpensive electric toothbrush to simulate the high-frequency vibration of a buzz-pollinating bee. The vibrating head is gently pressed against the flower stem or the back of the anther cone for a few seconds. The vibration travels through the plant tissue, causing the pollen to puff out of the anthers and settle onto the stigma.
Pollinating every two to three days ensures newly opened flowers are treated. This frequency is important because high humidity can cause the pollen to become sticky, making it difficult to release without assistance.