In a tweet send out by Lea Valley Growers it becomes clear that 'storms and glasshouses do not mix well'. The young plants are in the cold wind due to the sidewall of the greenhouse being shattered by the wind. About 50 kilometers north of London several nurseries are situated in the Lea Valley.
The UK and Ireland are being hit hard by Eleanor. The Met Office said Great Dun Fell, the second highest peak in England's Pennines, was hit by 100mph winds overnight, while parts of Northern Ireland suffered gusts of up to 90mph. Around 22,000 houses in Northern Ireland and scores more in England were affected by power cuts.
Why you should close the air vents in case of storm
One of the main results of a recently conducted study is that the outside edges of the modern greenhouse are most vulnerable. To reduce this vulnerability you should keep the air vents situated in the edge of the greenhouse closed (approximately the first 30 meters from the edge of the greenhouse on the wind side). When you leave the air vents in this area open, the greenhouse misses the constructive connection of the roof itself. For the air vents themselves: in an open position they are more likely to deform during a storm and therefore increase the risk of sheet breakage.
Besides the constructive aspect it has always been difficult to determine what the leeward and windward side of the greenhouse is. In the old rule of thumb Hagelunie opened all the vents on the leeward during a storm. But it is practically impossible to determine the leeward when the wind is perpendicular to the end gable. When the wind is blowing in an angle to the end gable it seems easier.
However, in case of a storm the direction of the wind can change about 30⁰ within one hour. This means the leeward side of the roof can change to the windward side with all detrimental consequences. As a result, and based on the TNO research the ISSO comity now advises a new golden rule: close all the air vents in case of storm.
What can you do to prevent damage?
- Precautions in case of storm:
- Close all air vents of the greenhouse
- For pressure relief the air vents can only be opened beyond the 30 meter limit of the exposed gable. If you feel the need you can open the vents in the opposite departments (3,4) on the leeward side of the ridge. Open the vents approximately 5 cm.
- Close the screens (on a packet). This prevents damage of the screen by falling glass. In case of damage after a storm the screens can be very helpful to maintain the climate.
- Prevent loose parts, like plastic boxes for the crop, from blowing in. Tie up parts outside the greenhouse before the storm arrives.