Tomato flowers can self-pollinate, but self-pollination still requires pollen to leave the anthers, reach the stigma, adhere there, and remain viable long enough for fertilization. Greenhouse humidity affects these stages differently. A flower-level observation is more informative than treating one room reading or a bee visit as proof that fruit set will follow.
Release: pollen must be dislodged
UConn Extension explains that dense greenhouse plantings may not receive enough natural wind to jostle tomato flowers. Vibration, including bumblebee buzz pollination, is described as a mechanism that dislodges pollen from the anthers. This explains why a self-pollinating flower can still have poor or uneven fruit set when release is inadequate. (UConn Extension)
Transfer: release is not reception
Once pollen is released, it must be transferred onto the stigma. The University of Maryland describes tomato flowers as complete flowers and pollen as heavy and sticky, requiring jostling to move from the male structures to the female stigma. It also links poor pollination with temperature stress and describes marks on flowers as evidence of bee visits. A visit record and a later fruit-set observation answer different questions; keep pollen release, stigma reception, and fruit development separate. (University of Maryland Extension)
Humidity, adhesion, and flower position
The Alberta government’s commercial greenhouse material distinguishes pollen release from pollen adhesion. High humidity can impede release, while drier conditions can reduce how well pollen adheres to the stigma. Temperature also affects pollen viability and pollen-tube development. These relationships do not produce one universal RH or temperature target, especially because flower conditions can differ near the canopy top even when a sensor reports acceptable air.
Flower position and temperature history therefore help put a room-level humidity reading in context. (Alberta.ca)
Interpret the stages together
For a greenhouse review, separate release, transfer, adhesion, and fertilization in the question being asked. Record crop zone and flower position beside the relevant air and flower observations, then bring unresolved fruit-set concerns to a qualified crop advisor. For the broader airflow context, see practical techniques for optimizing greenhouse ventilation.
Related project questions
Fruit set and fruit quality are separate observations. Continue with tomato cracking and differences between crop humidity zones. For the wider project context, return to agricultural humidity control.
