In the first part of this three part series on air ventilation in cannabis grow rooms we cover the benefits and “why” proper ventilation and circulation is so important. Our journey continues as we consider the variables and equipment necessary to get the job done.
Part 2 of our grow room ventilation series focuses on “how” to create proper airflow and the best ways to set up a ventilation system in several different grow room sizes.
In Part 3, we will cover the needed equipment and help you navigate the task of selecting the right equipment for your space.
This series will explain the physical and biological reasons for each article’s focus in simple terms. As we begin our three-part adventure into the exciting world of cannabis grow room ventilation, we aim to answer your most basic question: Why does any of this matter?
TL/DR
Controlled wind builds stronger plants
Multiple fans are better than one
Circulation reduces your chances of mold and bud rot
Airflow drives photosynthesis and increases yields
Table Of Contents
Why Is Ventilation So Important for Growing Weed Indoors?
The correct application of ventilation for indoor gardens can make the difference between a healthy crop and a ruined crop of cannabis plants. Airflow can be the difference between a weak and floppy plant or one with thick and sturdy branching. Wind is a primary source of mechanical loading in nature (structural stress), and it is also an important tool in temperature regulation. This single force of nature can influence growth, morphology, physiology, and reproduction.
In this section, we will present plants’ biological reactions to this outside stimulus and the functions that will be affected. Using basic plant physiology principles, we can manipulate our cannabis plants to grow healthier and stronger and provide larger yields! Some people may see the word “ventilation” and think of venting air out. However, ventilation is defined as moving air into, out of, or within a room/building or all of the above combined; it can also be referred to as airflow.
A huge cannabis plant thriving under the open skies.
Good Air Flow Strengthens your Cannabis Plants
From the day your ILGM cannabis seeds break the soil outdoors, natural airflow (the wind) acts as a strength and conditioning coach. It may blow from the north, or it may blow from the east, but whichever direction it is blowing from, the plant’s reaction is to build thicker and stronger cell walls to support the main stem against the forces of the wind.
Strong branches are essential to supporting large flowers later in the growth cycle. Applying gentle airflow to indoor cannabis plants can help strengthen the main stem and branches. The artificial airflow from fans within a grow tent generally comes from one direction and at a constant pace, unlike the wind gusts and occasional storms experienced by plants outdoors.
In the early seedling stage, giving your indoor plants a half turn each day to equally distribute the impacts from the artificial airflow can be beneficial. It is best not to point fans directly at seedlings; instead, bounce the air off the tent walls to create a swirling action around the young plants. As they develop, they’ll tolerate stronger forces. Oscillating wall fans in opposing corners of your grow tent can create the gust-like conditions experienced in an outdoor garden.
Oscillating fans ensuring air movement in a growroom with cannabis plants.
Air Circulation Regulates Temperature in Your Growroom
We all know how good a cool breeze can feel on a hot day. Outdoor cannabis enjoys the same sensation and can effectively use wind to regulate temperature. On a hot day, we often wipe our faces with a towel of cool water to help control our temperature. This phenomenon is called evaporative cooling. Cannabis leaves experience this as they transpire, reducing the leaf surface temperature.
In nature, temperature varies at different times of the day, and each day is often different than the last. Indoors, we can control the climate minute by minute. Growers can keep the room temperature steady within a few degrees every day. To discover the best temperature for your grow room, check out our article on the Best temperature for growing marijuana plants.
High-pressure sodium (HPS) bulbs emit heat directly towards the canopy. Using airflow horizontally, directly above the canopy, can move that hot air away and provide evaporative cooling. LED lighting directs a significant portion of its heat signature away from the plants, which can lead to lower leaf surface temperatures. Vertical airflow from the top of the tent downwards can direct the warmer air towards the canopy if growing indoors in colder climates.
Improve ventilation in a grow room with marijuana plants.
Airflow Encourages your Cannabis to Photosynthesize
Similar to nutrients and light, plants can have either excessive or deficient levels of wind in the grow space. The optimal wind speed to encourage photosynthesis only breaks through the leaf boundary layer surrounding the stomata. Too much or too little wind can result in lower yields. Learn more about the role of photosynthesis by reading the article, Photosynthesis in marijuana plants.
Due to an increased leaf boundary layer, photosynthetic rates lower at very low wind speed levels. Additionally, very high wind speeds combined with low ambient air temperatures (important for those using LED lights in the winter) can reduce photosynthesis due to a lower leaf surface temperature and stomatal conductance. Basically, photosynthesis in cannabis slows down quickly as the temperature drops, while the leaf boundary layer often thickens at high temperatures, inhibiting optimal photosynthesis.
Because photosynthesis drives cannabis growth and is directly related to temperature, it is important to control this parameter effectively. Ambient temperature, ventilation, and water stress can affect leaf surface temperatures. Air flow around the plants can affect the photosynthetic rates in cannabis because air flow affects other parameters like temperature, humidity, and the leaf boundary layer.
Caution: direct wind on cannabis plants can enhance water stress in dry soil conditions.
Proper airflow enhances the photosynthesis process in your cannabis plants.
A Good Airflow Avoids Microclimates (humidity and respiration)
Microclimates are pockets of higher or lower temperature, humidity, carbon dioxide (CO2) levels, etc., within a growing environment. For cannabis, moist, hot air is often responsible for creating microclimates when there is inadequate air movement. Stale, non-circulating (stagnant) air can stifle growth and lead to other problems, which we will cover shortly. First, allow me to explain what a leaf boundary layer is and why it contributes to both humidity and respiration.
Although an invisible force field would be a cooler answer, the leaf boundary layer (a form of microclimate) is the area around the stomata found on the underside of leaves. Cannabis transpires (sweats) through the stomata. Transpiration in a dense canopy with no air movement can create a boundary layer of humidity around the leaves. Stomata are also where plants exchange gases like oxygen and carbon dioxide. With little to no air movement, CO2 levels are reduced within the leaf boundary layer, indicating lower respiration.
The leaf boundary layer is broken by providing adequate airflow within the canopy, which will increase CO2 uptake, respiration, and photosynthesis. Properly designed air circulation can also displace moisture from within the leaf boundary layer, reducing humidity and stimulating further transpiration, leading to increased nutrient uptake.
Caution: too strong of a wind directly on the plant can keep the stomata open, leading to potential nutrient problems.
Reduce the Chances of Pathogens on Your Cannabis Plants
Constant airflow in the garden space is essential to a good integrated pest management (IPM) strategy. Powdery Mildew (PM) and botrytis thrive in stagnant, warm, moist air areas. A constant breeze in and around the canopy can reduce the likelihood of fungal outbreaks. Defoliating is another technique growers use to reduce humidity within the canopy. For more on that, read the Cannabis Defoliating 101 article.
Avoid overfilling your grow tent; a high plant density can trigger fungal outbreaks and lead to bacterial disease. When soil remains wet for an extended period, it can become a hotspot for pests like fungus gnats. A steady breeze can increase transpiration, causing the roots to uptake water and dry the soil faster. A steady breeze can also create undesirable conditions for other pests and act as a deterrent.
The air is often brought in from outside the building in large grow rooms as part of the ventilation chain. Along with the additional CO2, pathogens, molds, and pests can hitch a ride in on the air stream. Intake sources at ground level or near vegetation increase the risk of introducing these problems. Growers should use filters capable of filtering pollen, pathogens, bacteria, and pests on any air introduced into the grow space from outdoors.
Increase Yields and Quality of Your Buds
An unseen benefit of using wind to strengthen cannabis seedlings is that the roots undergo similar growth in response to wind stress. It produces a deeper, larger network of roots in the soil to survive the forces trying to blow the plant over. There is a saying in cannabis – the bigger the roots, the bigger the fruits. Root health directly relates to yield and the quality of your buds.
Photosynthesis also drives root growth. As we’ve just learned, a plant won’t photosynthesize properly if the leaf surface temperature isn’t in the right range. The plant won’t photosynthesize as effectively if the leaf boundary layer is too thick. Essential elements used in photosynthesis, like CO2, are in lower supply near the stomata if the air is stale. We can use ventilation to correct these problems and maximize photosynthesis.
With award-winning ILGM genetics firing at their fullest potential thanks to proper ventilation, amazing yields of high-quality flower are just around the corner. Now that you understand some of the “why” behind ventilation, you may wonder how best to accomplish this in your grow space. For the next step in the adventure, continue to part two: How to create good airflow.
Conclusion
Proper ventilation is a catalyst for healthier plants and larger yields. Wind can also deter pests, making circulation within the grow space part of an effective Integrated Pest Management (IPM) strategy. It breaks up pockets of moist, hot air surrounding leaves along the inner canopy. It can also help regulate leaf surface temperature, promoting higher rates of photosynthesis.
Regardless of the size of the grow room or the number of cannabis plants in it, the importance of a well-planned grow room ventilation system remains the same. Fresh air needs to come in; it needs to be circulated within the space, and then it must be exhausted. To expand your knowledge of good airflow and how to create it, check out Part Two of this series: How To Create Good Air Circulation In Your Cannabis Grow Tent.To learn more about other aspects of cannabis growing, download Robert’s Grow Bible. We hope this article has blown you away. If you have any unresolved questions about this article or air flow in general, share them in the comments below.
Comments