![]() ![]() A natural ventilation system is a system that has no powered fans but instead relies on wind and thermal buoyancy for air movement. When building a greenhouse or setting up a ventilation system one of the first decisions a gardener must make is whether to use a natural or mechanical ventilation system. Natural (Passive) or Mechanical (Powered) Ventilation Systems Air movement within a greenhouse could be the determining factor as to whether a plant is pollinated and able to complete its reproductive cycle. Many vegetable and ornamental plants are pollinated via the wind. For many plants wind (or the simulation of) serves an even more integral purpose: pollination. Wind strengthens the cell walls of a plant’s stem and directly influences the architectural integrity of plant growth. Air movement is also our way to simulate the wind in an enclosed environment. Plants respond better to environmental consistency and proper air circulation ensures each plant within the greenhouse receives the same atmospheric conditions. Proper air circulation creates uniformity in temperature, humidity, CO2, and oxygen within the environment. Air CirculationĪir circulation, or air movement, within a greenhouse serves many purposes. Oxygen is required for the roots to continuously grow and is therefore directly linked to the plant’s ability to uptake nutrients. Although plants create their own oxygen they still benefit from the replenishment of oxygen found in fresh air. We all know plants “breath” CO2 and expel oxygen but many people do not know that plants (more specifically plant cells found in the rhizosphere) absorb oxygen in its gaseous form. Maintaining an adequate level of fresh air intake guarantees sufficient CO2 levels for plant growth. When CO2 levels decrease the rate of photosynthesis and all other plant functions associated with photosynthesis decrease accordingly. During photosynthesis, plants use CO2 which they acquire directly from the air. Fresh air drawn into a greenhouse carries with it two important gases needed by plants to carry out some of their most basic functions. Just as humans would run out of oxygen in a poorly ventilated and enclosed area, plants “breath” CO2 which needs to be replenished in any greenhouse that is not supplementing it artificially. It is also very common for the environment within a greenhouse to be affected by the dew point which causes condensation and excess humidity. Plants transpire moisture that, if not removed, can build up in a greenhouse, raising the humidity levels. Just about every mold, fungus, and mildew thrive in high humidity conditions. Although some varieties of plants thrive in high humidity conditions, most plants are hindered by the pathogens associated with high humidity levels. Like heat, high concentrations of humidity can become trapped in a greenhouse’s environment. ![]() Ventilation systems, whether natural (passive) or mechanical (powered), serve the basic function of the removal of excess heat. If this heat is not removed from the environment it can cause undesirable conditions for plant growth or worse. Greenhouses trap solar radiation thereby raising the temperature in the environment (the greenhouse effect). Greenhouse ventilation systems serve four imperative functions: temperature control, humidity control, CO2/oxygen replacement, and air circulation. Not only are ventilation systems vital to maintaining environmental conditions but they also directly influence a plant’s ability to perform photosynthesis, uptake essential elements, and complete reproductive cycles (pollination). Most gardeners understand the importance of ventilation systems for temperature control but benefits derived from ventilation systems are multifaceted. Many novice horticulturalists do not attribute slow growth, poor yields, or problems with pathogens to an inadequate greenhouse ventilation system. The greenhouse ventilation system plays a pivotal role in plant health and crop production. ![]()
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