Greenhouse insect netting and airflow: the trade-off buyers miss
The smallest pest usually asks for the finest mesh. The crop may disagree. In greenhouse insect netting, pest exclusion and airflow pull in opposite directions: smaller apertures block smaller insects, but they also make ventilation harder.
In short
For greenhouse insect netting, specify the target pest first, then confirm the aperture in millimetres and the ventilation impact. Fine mesh can stop thrips and whiteflies, but it may raise heat and humidity under cover. The right specification is the largest aperture that stops the target pest while keeping enough airflow for the crop.
Why fine mesh is not automatically better
If a buyer only thinks about pests, the logic is simple: choose the finest mesh available. That logic breaks when the crop starts sitting in hotter, more humid air.
University and extension guidance on insect screening repeatedly warns about airflow reduction. Bethke and Paine showed that exclusion depends on more than hole size, and North Carolina State University’s greenhouse screening bulletin explains the practical problem: smaller openings increase resistance to air movement.
In plain English: the net may stop the insect and still create a crop problem.
The specification sequence
Do not start with “50 mesh”. Start here:
- Target pest.
- Approximate aperture in millimetres.
- Crop and climate.
- Greenhouse ventilation type.
- Roll width and installation location.
- UV treatment and expected outdoor exposure.
For the pest side, use the Mesh Size Visualizer. For the quantity, use the Netting Coverage Calculator.
A practical example
If thrips are the main pest, the starting aperture is around 0.19 mm. That is very fine. If leafminers are the target, the starting aperture is closer to 0.64 mm. Those two nets are not equivalent from an airflow perspective.
So a quote request that says “insect netting for greenhouse” is incomplete. The supplier needs the pest and crop, not just the building.
What to ask before buying
Ask the supplier:
- What is the aperture in millimetres?
- Is the quoted mesh count tied to actual opening size?
- What is the material and UV treatment?
- What roll widths are available?
- Has airflow reduction been considered for this installation?
If the answer is only “high quality insect net”, keep asking. “High quality” is not a ventilation plan.
Sources
- Bethke, J.A. and Paine, T.D., “Screen Hole Size and Barriers for Exclusion of Insect Pests of Glasshouse Crops”, Journal of Entomological Science, 1991: https://doi.org/10.18474/0749-8004-26.1.169
- Bell, M.L. and Baker, J.R., “Greenhouse Screening: Comparison of Materials for Excluding Thrips and Whiteflies”, North Carolina State University, 1995: https://hortscans.ces.ncsu.edu/uploads/g/r/greenhou_559d702f7c978.pdf
Frequently asked questions
Is finer mesh always better for greenhouse insect netting?
No. Smaller openings increase resistance to air movement, which can raise heat and humidity under cover. The right specification is the largest aperture that stops the target pest while keeping enough airflow for the crop.
What aperture is the starting point for thrips?
If thrips are the main pest, the starting aperture is around 0.19 mm. For leafminers it is closer to 0.64 mm. Those two nets are not equivalent from an airflow perspective, which is why the pest must be stated.
Why is "insect netting for greenhouse" an incomplete request?
Because the supplier needs the pest and the crop, not just the building. Specify the target pest first, then the aperture in millimetres, crop and climate, ventilation type, roll width and UV treatment.
What should I ask a supplier before buying greenhouse insect netting?
The aperture in millimetres, whether the quoted mesh count is tied to actual opening size, the material and UV treatment, available roll widths, and whether airflow reduction has been considered for this installation.