The Impact of Different Air Exchange Rates on Cannabis Growth

The impact of different air exchange rates on cannabis growth

Cannabis plants grow best when growing in an environment with sufficient CO2 and good air quality. These conditions ensure that the plant absorbs all of the nutrients it needs to thrive, and prevents the development of nutrient burn and mould issues.

This is especially true for equatorial strains, which can have trouble flowering in indoor environments or northerly latitudes. As a result, they may switch back and forth between vegetative growth and flowering, or experience copious mould.


Temperature is a critical factor for cannabis growth, as it determines the rate at which plants absorb water and the effectiveness of their photosynthesis. Typically, cannabis plants prefer a temperature range from about 68 to about 77 degrees Fahrenheit when they are in their vegetative stage. They can tolerate slightly lower temperatures when flowering.

The temperature of the grow room should be maintained between 75 and 85 degrees Fahrenheit under optimal conditions. This helps ensure the plant can absorb the CO2 it needs to thrive and produce quality buds.

Maintaining a constant humidity level is also crucial for cannabis cultivation. The right humidity will protect your plants from unwanted diseases, like mold and mildew, which can ruin the quality of your buds.

Humidity should be between 40 and 50 percent during the flowering stage. This allows the roots to absorb more water, preventing dry leaf spots that can cause premature dry-out and lowered resin production.

Depending on the plant’s needs, different wavelengths of light can be used in the grow room. During the vegetative stage, blue light between 400 and 500 nm is ideal for growing strong, healthy leaves. Red light between 620 and 780 nm is best for the flowering stage, when it will produce larger, more resinous buds.

When choosing the right grow lights, look for ones that emit less heat than HPS or other high output lamps. Avoiding these types of lights will help keep your grow room cool without sacrificing a high yield.

As the growing season progresses, your grow room’s HVAC control becomes even more important. You will want to set the proper temperatures for harvesting and drying your buds, so they don’t dry out or damage terpenes before you get them to the store shelf.

During the flowering stage, your cannabis plants will need to produce lots of trichomes on their buds, which can be difficult to achieve if your grow room is too hot. Cold weather during the final weeks of flowering can make it easier for your cannabis to produce the resin they need, resulting in beautiful, fragrant buds with an increased concentration of trichomes.

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Humidity is a crucial factor in cannabis growth because it affects how much water your plant can drink. It also changes how many nutrients your plants can absorb, which in turn can impact their health.

Cannabis is an extremely nutrient-rich plant, which means that it is very sensitive to over or under-hydration. Often, this can have negative consequences for your plants, especially during the flowering stage of their life cycle.

In order to maximize the potential for your plant to produce a bumper crop, it is vital that you control the humidity level within your grow room. This can be done using a dehumidifier, increased ventilation or both.

The amount of moisture in the air is called relative humidity (RH), and can be measured using a device such as an electronic hygrometer. The RH levels in a grow room should be kept between 40 and 70 percent during the vegetative stage of growth, and reduced to around 50 percent during the flowering phase.

Seedlings and clones prefer high humidity, as it allows them to uptake water through their leaves until they develop roots. They do not require a humidity dome, though it can be beneficial to provide one for them if it is incredibly dry where you live.

Once a cannabis plant has developed its root system, it can begin to grow more quickly and yield more buds if the grow room is maintained at the correct level of humidity. This is important because if the plants don’t get enough water, they may not develop the proper structure needed to withstand mold and mildew.

A lower humidity is also needed to prevent bud rot, which is an invasive mold that can be harmful to cannabis flowers. If a fungus is present, it can cause the buds to turn brown, which makes them less likely to have the sparkly trichomes and other crystalline structures that you expect from your buds at harvest time.

You can also use a dehumidifier to lower the humidity in your grow room during the last few weeks of flowering to improve resin production. However, it is important to note that lowering the humidity too much can stress your plants, which might not be optimal for all strains.

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Cannabis sativa requires adequate light intensity and the right spectrum to trigger photoperiodic and photomorphogenetic responses for efficient conversion of carbon dioxide into biomass, root development and flowering. The spectrum of photosynthetically active radiation (PAR), ranging from 400-700 nanometers, is essential to efficiently drive plant growth and the conversion of carbon dioxide into terpenes and cannabinoids in Cannabis flowers.

Green light has a direct impact on morphology of Cannabis plants, causing them to enlarge their leaves and extend their stems. Lower levels of green light cause plants to form smaller leaves and shorter stems, while higher proportions promote a taller plant with large leaves.

Blue light, on the other hand, triggers a protein called the Zeitlupe family that regulates the circadian clock. This is particularly beneficial for Cannabis because of its high cannabinoid content, and a blue-light regime that activates this function should be able to enhance yield.

Red and far red light are also effective in promoting morphology, especially stem elongation. Despite the fact that this light is not included in the PAR range, testing has shown it can be a positive influence on cannabis growth and photosynthesis.

The ratio of red to far-red in the PAR spectrum, known as the R:FR ratio, is important for a variety of plant species and cultivars, including Cannabis. The R:FR ratio influences a plant’s morphology, but is not believed to affect flowering times.

In horticultural research, a wide range of light sources have been used in cannabis cultivation. These include fluorescent bulbs, metal halide (MH) and high-pressure sodium (HPS) lights.

As a result, different lighting strategies are being developed that optimize the light spectrum at various stages of Cannabis growth, while avoiding any spectral shifts that negatively impact the photobiology of Cannabis. This will help maximize quality and terpene production.

The intensity of light is an important factor in the overall success of a grow, as it affects the size and color of the Cannabis plants as well as their photosynthetic rate. A low light intensity can have an adverse effect on yield, while a high light intensity has the opposite effect. In addition, the uniformity of light can vary greatly between sources and heights, which can lead to inconsistent results.

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Air Exchange

As with all aspects of cannabis cultivation, proper air movement and ventilation is crucial for healthy cannabis plants. It can help regulate the temperature, maintain a steady flow of oxygen and carbon dioxide, and prevent mold and mildew growth. Ventilation also helps keep humidity in a manageable range and prevents fungus and pest infestation.

For this reason, all cannabis grow rooms and tents need to be well ventilated and exhausted on a regular basis. While there is no hard and fast rule on air exchange rates, it’s generally advised to have the complete volume of the room or tent refreshed every three minutes.

The amount of air exchanged depends on many factors including the size of the grow space and the lighting. Ideally, each grower should determine what their optimal air exchange rate is by studying the plant’s growth pattern and checking the temperatures inside and outside of their grow room.

When a cannabis plant is small it has minimal levels of photosynthesis and respiration, but as it grows and increases its leaf area so does the need for good ventilation. In nature this would be handled by a simple breeze, but in an enclosed grow room it is the growers responsibility to ensure sufficient ventilation is available to remove excess moisture and pollutants from the grow space.

A properly designed ventilation system involves ducts running through the walls that end with fresh air distribution grilles and stale air exhaust grilles. The ducts take the stale air out of the grow room and replace it with new outside air.

This process is called air exchange and it enables a steady and continuous flow of fresh air into the cannabis grow room. Without adequate ventilation your cannabis plant will struggle to thrive and produce a high quality crop of buds.

If you have a strong fan you can exchange the air in your grow room once every 2-3 minutes. This is the recommended air exchange rate for most growers as it gives you the best chance of keeping your cannabis plant healthy and producing quality buds.

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