The key to any successful greenhouse is a proper ventilation system. Ventilation systems in greenhouses serve four key functions: air circulation, CO2/Oxygen replacement, humidity control, and temperature control. The main function of ventilating a greenhouse is to remove warm, moist air, and replace it with drier air. Because high humidity causes unwanted condensation and increases the occurrence of disease and mold in your plants, it is extremely important to have proper ventilation.
Proper airflow also promotes a balanced environment necessary for photosynthesis. All plants need carbon dioxide in order to photosynthesize and produce the sugars they use as food. If your greenhouse does not have good air flow, the plants will not have the CO2 necessary to thrive. Plants naturally transpire (sweat) moisture by “breathing” CO2 – if this is not maintained at a safe and balanced homeostatic level, the excessive humidity put off by the plants can lead to mold, mildew, fungus, and other unwanted growths that can pose damage or even death to your crops. Regardless of the type of greenhouse or greenhouse covers you are using, having the proper ventilation is crucial to avoid these complications.
There is a common misconception that using a ventilation system is not necessary if growers utilize a breathable greenhouse cover; however, that concept will cost greatly in time and money! A proper ventilation system is always required in order to prevent overheating and moisture build up. Greenhouses work by simulating what’s called the “greenhouse effect:” when solar radiation (light) is contained, it is converted to heat. However, without proper ventilation, the trapped heat – in addition to the CO2 naturally produced by plants – creates humid, moist air that inadvertently sabotages plant growth.
Types of Ventilation Systems
There are different ventilation systems available, depending on the type and size of greenhouse you have. The main two are passive ventilation (natural), and mechanical ventilation (machine powered). Mechanical ventilation (exhaust fans) is ideal for larger commercial greenhouses, with use of equipment such as fans or other mechanical devices that are used to move air and control circulation. For smaller applications, passive air ventilation is successful because the greenhouse will naturally get rid of excessive heat as the hot air rises to the surface to exit the vents. There are other types of vents that may be used in a simple greenhouse design by simply attaching it to an opening directly onto the cover. Vents are extremely important and should always be left open during warm weather; ideally, vents should be placed near or on the roof of the greenhouse in order to allow heat to escape. It is also recommended to place several vents near the base of the perimeter of the greenhouse to allow cross ventilation. Cross ventilation, the process by which cool fresh air freely enters the greenhouse through the bottom vents and flows across towards the top vents, allows heat to escape and enables a consistent supply of fresh CO2 for your crops.
What is Light Deprivation?
Light deprivation, also known as light dep, is a technique used to “trick” plants into growing year-around by blocking sunlight. Light dep can be accomplished several ways depending on the grower’s budget and crop size. Choosing the right light dep process can be daunting – there are so many options! For example, panda and BOLD® are commonly used films for light dep greenhouses; however, they differ greatly in quality. While panda can be slightly less expensive, it doesn’t contain a tear resistant layer of scrim and only has a 1-year lifespan at full exposure. Alternatively, BOLD® is totally light blocking, UV resistant, heat reflective, FDA compliant, and has up to a 2 year lifespan at full exposure. BOLD® provides total darkness for an extended period of time throughout the rigorous day to day covering and uncovering during the grow season, an impressive task that other films cannot do.
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