Quick answer: Greenhouse tomatoes are self-fertile, but their pollen must be shaken loose from the anthers (by bumblebees, vibration or air movement), land on the stigma and stay viable. Humidity affects each step: in very humid air (above roughly 80–85 % RH) pollen tends to clump and release poorly; in very dry, hot air, pollen and stigmas dry out and lose viability. Pollination usually works best around the middle of the day, with moderate humidity (roughly 60–80 % RH) and temperatures in the normal growing range. Avoid very high night humidity that leaves flowers damp into the morning, and avoid heat above about 30–32 °C during flowering.
Quick answer
- Release needs vibration (bumblebees, vibrators) and moderately dry air.
- Very humid: pollen sticks and clumps. Very hot and dry: pollen loses viability.
- Best window: late morning to early afternoon, moderate RH.
Three steps, three humidity effects
| Step | What happens | Role of humidity and temperature |
|---|---|---|
| Release | Pollen leaves the anthers when flowers are vibrated | Damp pollen clumps; release is better in moderately dry air |
| Transfer | Pollen reaches the stigma (self-pollination within the flower) | Bumblebee buzz pollination or vibration; dense, still canopies give little natural movement |
| Germination | Pollen germinates on the stigma and grows to fertilise ovules | Very high temperatures and very dry air reduce viability |
UConn Extension notes that dense greenhouse plantings may not get enough natural movement to release tomato pollen, and describes vibration and bumblebee pollination (UConn IPM). The Government of Alberta's greenhouse tomato guidance covers pollination in commercial production (Alberta), and the University of Maryland describes pollination problems in high-tunnel tomatoes (UMD Extension).
A daily climate plan for good fruit set
| Time | Aim |
|---|---|
| Night | Keep humidity below saturation so flowers are dry by morning; see tomato greenhouse humidity |
| Early morning | Raise temperature gradually; dry the canopy before pollination hours |
| Late morning to early afternoon | Moderate RH and temperature; bumblebees active; vibrate flowers if hand-pollinating |
| Hot afternoons | Shade and ventilate to keep flowers below about 30–32 °C |
Related: tomato greenhouse humidity.
Choose late morning to early afternoon for tomato hand-pollination, when humidity is roughly 60–80 % RH and temperature is in the normal growing range.
Signs of poor pollination
- Flowers drop without setting fruit.
- Misshapen, small or seedless (puffy) fruit.
- Few bumblebee "bite marks" (bruising on anther cones) when bees are used.
- Fruit set falls during long humid or very hot spells.
Humidity control for pollination
- Night dehumidification keeps flowers dry and pollen in good condition for the next day; see greenhouse night-time humidity.
- Air movement (HAF fans) helps pollen release and keeps flowers dry.
- Avoid fogging or misting during pollination hours.
- Our greenhouse dehumidifiers support night humidity control when venting is not enough.
FAQ
Frequently asked questions
What humidity is best for tomato pollination?
Moderate humidity, roughly 60–80 % RH, during the pollination hours; very high humidity makes pollen clump.
Does high humidity stop tomato pollination?
It reduces pollen release and transfer; very humid nights that leave flowers wet also cause problems.
What temperature prevents tomato fruit set?
Long periods above about 30–32 °C during flowering, or nights much colder than normal growing temperatures, reduce fruit set.
Sources
- UConn IPM, Pollination of greenhouse tomatoes.
- Government of Alberta, Commercial greenhouse tomato production.
- University of Maryland Extension, Problems with pollination in high-tunnel tomatoes.
