Ventilation is critical to successful greenhouse crop production. Greenhouse ventilation goes beyond temperature control, greenhouse exhaust fans, circulatory fans, and shutters (louvers). It plays an integral role in controlling environmental conditions for humidity, gas exchange (CO2/O2), and air circulation. Plant processes like photosynthesis, nutrient uptake, and reproduction are reliant on having the proper balance between all of these factors.

Without proper greenhouse ventilation, crops can experience slowed growth, poor yields, and have an increased risk of pathogen exposure. In addition to poor crop production, excessive temperatures and improper ventilation will increase costs for electricity and watering. Ventilation is even more critical if heat-generating supplemental lighting (like HID bulbs) are being used in a greenhouse.

Mechanical vs natural ventilation is a hotly debated topic. Many factors determine which ventilation method may be best for your operation. That being said, a number of recent university agricultural studies suggest that mechanical ventilation has many benefits that are hard for growers to ignore. Comparing mechanical vs natural, mechanical greenhouse ventilation produces more consistent results and is less dependent on weather.

Most growers elect to choose either mechanical or natural ventilation. So which should you choose? The following study, "Mechanical and natural ventilation systems in a greenhouse designed using computational fluid dynamics" is a bit thick in the academic sense but interesting to look at. The result of the study suggests that both mechanical and natural ventilation methods combined offer the best ventilation results, especially in regards to maintaining uniform temperatures throughout your greenhouse.

The core considerations with manual vs natural greenhouse ventilation are cooling effectiveness and uniformity. That said, installing powered roll-up sides, powered ridge vents, exhaust fans, and powered louvers, along with a bunch of light traps for light dep at intake and exhaust vents is costly.

In comparing natural vs mechanical greenhouse ventilation, up-front costs can be similar. The natural ventilation method lowers operational energy costs but is known to produce inconsistent results if wind speed drops below 2-3mph. The mechanical ventilation method provides better control which many cultivators ultimately prefer especially when paired with light deprivation.

Furthermore, you may orient your greenhouses differently depending on what your long term ventilation method will be. If you will be naturally ventilating priority goes to the greenhouse orientation is best when it is towards prevailing winds. If your long term plan is to cool mechanically you’ll want to orient the sides of your greenhouse towards the sun’s day arc to maximize light since your airflow is mechanized.

Ventilation systems are needed to remove excess heat and humidity. Ventilation can be automated or manual, and passive or active. The size of your greenhouse operation, your budget, and your climate will determine which is best. Growers who plan to use their greenhouse over the cooler seasons, and growers cultivating temperature-sensitive plants will also have to consider heating options.

Hortitech Direct offers many options for greenhouse kits with both automated and manual ventilation! This article is very much a simplified answer. Your strain, climate, greenhouse size and shape, and other factors will affect what ventilation method is best for your plants. If you’re on the fence give us a call and we’ll help you sort it out.