Only open bumblebee boxes when the bumblebees can make use of natural light. In dark periods, bumblebee boxes are usually opened between 9 a.m. and 10 a.m. and closed after 2 p.m. and 3 p.m. On a very dark day, you can have decided not to open the bumblebee boxes.

Fog and snow ensure that less natural light enters the greenhouse - and snow also ensures that the light that does enter the greenhouse is enormously bright. This influences the orientation of bumblebees. Heavy fog or snow can cause you to lose 10 - 25% of your bumble bee population in one day. If you know that fog or snow is coming, take this into account when opening and closing the bumblebee boxes:

• If it is foggy in the morning and the bumblebee boxes are not yet open, postpone this until after the fog.
• If snow is predicted during the day, make sure to close the bumblebee boxes in time.

If the fog or snow lasts longer (2 - 3 days), it is advisable to use a few extra bumblebee boxes to compensate. Use half a bumblebee hive per hectare extra.

In dark periods, you can also choose to place bumblebee boxes higher up in the crop. In this way, the bumble bees capture sunlight earlier in the day, so they can make maximum use of the available light. It also reduces problems of visibility and orientation on dark days. 

If you choose to place the bumblebee boxes higher, it is important that the bumblebee boxes are protected from direct sunlight. If you do not do this, there is a risk that the bumblebees will overheat on days with very intense sunlight. Also make sure that the bumblebee boxes are placed lower down in the crop in time, preferably in the beginning or middle of March (depending on the amount of sunshine).

In addition to raising the height of the bumblebee boxes, it is also advisable to spread the bumblebee boxes regularly along the main path. This way you keep the flying distances as small as possible. Also make sure that the boxes are clearly visible from the main path, so that the bumblebees can easily find them.

In greenhouses with paths longer than 70 metres, it is advisable to place the bumblebee boxes in at the front of the path and at the back of the path (against the façade). For paths longer than 130 meters you also place a bumblebee box halfway along the path. These measures are intended to reduce the flight distance. Place the bumblebee boxes halfway along the path and against the facade on top of the path so that the bumblebee box is visible.

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