How are tomatoes pollinated in the greenhouse?

A tomato flower has both male and female parts, and it can pollinate itself. So why do greenhouse growers bring in bumblebees? Because the pollen does not fall out by itself. It sits inside a closed cone of anthers and only comes out when the flower is shaken.

Buzz pollination

Outdoors, wind and insects shake tomato flowers. In a greenhouse there is little wind. Bumblebees solve this by holding on to the flower and vibrating their flight muscles at high frequency, without beating their wings. The vibration shakes pollen out of the cone, onto the bee and onto the stigma. This is called buzz pollination, or sonication.

Honeybees cannot do this, which is why bumblebees became the standard pollinator in greenhouse tomatoes. Before that, growers shook the flower trusses with electric vibrators, a job that took a lot of labour.

How tomatoes are pollinated in practice

• Bumblebees. The usual method in commercial greenhouses. Colonies are spread across the greenhouse and replaced on a schedule.
• Vibration by hand. Electric vibrating wands, or tapping the trusses or support wires. Still used in small greenhouses, in research and where bees cannot be used.
• Plant growth regulators. In some regions, fruit set is induced with hormone sprays instead of pollination. This is less common in modern greenhouses, partly because of the labour and the effect on fruit quality.

Conditions that affect pollination

Even when bumblebees visit, the flower has to release good pollen and the stigma has to receive it.

• Temperature. Very high or very low temperatures reduce the amount and quality of pollen. Hot days and cold nights both count.
• Humidity. Very humid air can make pollen sticky so it stays in the cone; very dry air can dry it out.
• Light and plant balance. Low light and a plant out of balance give weaker flowers.
• Bumblebee activity. Heat at the hive, screens, changes in lighting and crop protection all affect whether bumblebees fly. See why bumblebees stop flying in the greenhouse.

Poor fruit set in tomatoes

When fruit set is poor, first find out whether the flowers were visited. Bite marks on the anther cones show whether bumblebees have been there. If there are plenty of marks but set is still poor, look at climate, plant balance and nutrition. If marks are scarce, look at the hives: are the colonies active, are there enough, and are they well placed? See how many bumblebee hives per hectare.

From checking to measuring

Checking bite marks takes time and only shows a sample of visits from days ago. HiveWatcher measures pollination continuously. The HiveNode at each hive records flight activity and the conditions at the entrance. The BeeNode in the crop counts visits to the flowers as they happen. In the portal you see per section where pollination falls behind, before it shows in fruit set.

Read more about tomato pollination in the greenhouse, or take part in one of our pilots.

Read more about hive monitoring with HiveWatcher.