Why is air circulation needed for marijuana plants
Marijuana grows best when exposed to a constant supply of fresh air with lots of carbon dioxide. Plants consume CO2 similar to how humans require Oxygen. For outdoor grows this is provided by the wind. To replicate this indoors, its important to keep a constant stream of air movement to replenish the CO2 around your plants.
Your tent's exhaust system will provide the intake of new air. You'll need fans inside the tent for air circulation so this fresh air reaches all parts of your pants. Proper air movement will also prevent problems with plants, such as mold, mildew, and pests.
Plants respond to the wind by increasing the strength of their branches. Lots of air movement encourages strong, healthy branch structure which will be needed to keep top-heavy buds standing up close to the light.
How much air circulation do marijuana plants need?
You want the fans to be pointed right at your plants so that they're constantly rustling. The CO2 around your plants needs to be replenished at least every 5 minutes for optimal growth of marijuana plants. A gentle rustling is best. But based on your setup it can be hard to ensure uniform circulation.
Make sure not to overdo the air movement. Blasting a powerful fan may help the plants furthest away get nice air movement, but the plants right in front of the plant may show signs of wind burn.
Different lights may also impact how much air circulation your marijuana plants need. If you're running 1000 watt air-cooled lights in a tent, you'll still have to worry about temps and keeping the light far enough from your plants.
Try the hand test. If you place your hand under the light and it start to get uncomfortable, that's exactly how your plants will feel.
Increasing circulation above the canopy can reduce heat to the tops of your plants. But it's no cure for plants that are too close to hot lights, so always make sure to factor in your plant height when inducing flowering so that the additional growth in the flowering stretch doesn't raise your plant tips into the burn zone.
What Roles Do Fans Play In Ventilation?
Fans do play the most important role in the whole ventilation system of your grow room- no denial on that. Before you decide the on-off cycle of the fans, it's important to keep their functions in mind.
So let's have a glimpse at what it does for the whole system-
To Keep Plants Breathing
Plant's kind of respiration is to inhale the CO2 around the leaves and grow themselves through photosynthesis. And the process is continuous at both nights and days.
In ideal growing environments, plants use up the CO2 surrounding its leaves in every 20 or 30 minutes. So, you need to keep the airflow going on to let the plants breathe. And fans are the only tool in rescue.
Keeping The Temperature Comfortable
Fans keep the air flowing, and that keeps the temperature under control. Lack of regular air exchange through fans will increase the temperature inside, and that would be even worse due to the radiant heat from the lights(even when they are off).
Maintain the Correct Humidity Level
Too much humidity brings on unexpected pathogens to take a hold. And what's the most frequent reason for such a rise in humidity?
Poor airflow- you guessed it right!
Fans are once again, the tool you've to rely on to keep humidity level under control.
To Keep The Odor Under Control
Another secondary but important thing fans(specially exhausts) do is to keep the odor under control. If you've been growing for quite some time, you might be well aware of its importance.
What sizes and types of fans work best in grow tents
When choosing the best fan for your grow tent there are several consideration. In a large grow room, powerful oscillating fans can be used to maximize air coverage across a wide area. This isn't possible in a small grow tent, where clip on fans attached to a pole are a better option.
Inline/Extractor Fans
They're in charge of bringing/extracting air from or to the growing space. Another important role they play is to keep the temperature under control. And that mostly depends on the presence of lights.
So, the light/dark cycle of the plants plays a massive role to decide when to keep inline fans on and when to shut them off.
Oscillating stand fans
Large grow tents need a larger solution. Oscillating fans come in lots of sizes, including 8″, 10″, 12″, 16″, 20″, 24″, and 30″. Most of the larger sizes are available as stand fans. Since they deliver air in multiple directions, oscillating fans a great choice for ensuring lots of air movement around your happily-growing marijuana. If you have the room, go for it.
Large oscillating fans on stands work well in larger tent environments. Multiple fans are needed in bigger grow rooms, but the changes are if you're utilizing a very large grow tent you're probably not reading this tutorial on choosing the right tent fans.
How Long to Keep Fans on in Grow Tent
1.Based On Light/Dark Hours
How Long to Keep Fans when Light's Are On?
inline Fans
As long as the light system is on, you need to keep every inline air exchange system working- that's the rule of thumb.
The air exchange demand based on the heat and humidity produced can be determined through a cfm calculator. However, you should custom the fan speeds based on that.
Oscillating Fans
Same as the inline fans. Keep them rolling throughout the entire light period. It's best to stick them to their maximum speed if it doesn't reach trouble with the plants.
How Long to Keep Fans when Light's Are Off?
Inline Fans
Right after 15-20 minutes after the lights are off, you can reduce the speed of the inline fans using a speed controller. After a few hours(while the temperature and humidity are ambient) of doing so, you can run them on/off at a regular frequency.
For an example- you can keep using them for the first 15 minutes of each hour, and keep them off for the rest of the hour. And keep continuing the process until the next light period.
Oscillating Fans
When lights are no more on plants, no more heat is generated. And the photosynthesis process takes a break. But however, plants keep breathing and leaving vapors around the leaves.
So, oscillating fans still need to be on duty. But you can deduce the speeds by a few degrees with the default speed controller they come with. And keep them rolling like that till the next light period.
2.Based On The Stage Your Plants Are In
How Long to Run Fan on Seedlings Stage
For growers who grow on their own, ensuring proper ventilation is a must from the very beginning. And it all starts from the seedling stage.
New seedlings are quite vulnerable to diseases sourced from damping-off air. So, you need to ensure regular air circulation around them for 24/7.
You may schedule the exhaust fans based on the temperature and humidity, but the oscillating stand-up or tower fans should always be rolling on. Thus, it can prevent the soil from being dry, and keep a gentle breeze whining around the seedlings.
How Long to Run Fan on Flowering Stage
Flowering is the most important part of the whole growing process, specially for cannabis growers.
As always, both exhaust and oscillating fans should be running during the light hours. But when it comes to dark hours, you need to do some quickie maths.
In case you've 2-3 oscillating fans, 1 intake fan and 1 exhaust fan, keep the oscillating fans on for the entire dark period. And turn the other fans off after 1 hour after the light goes off. And turn them on again ½ hours before you turn the lights on again.
However, when your plants are in late flowering, they might stink with odor, and embarrass the whole space. So, the best policy is to run scrubber fans 24/7 at late flowering stage.
3.Based On Night/Day
Should You Keep Fans On or Off at Night?
This is one question we noticed growers to ask a lot.
Well, the answer is- it depends on how cold it is out in the night. To be more specific, colder nights would turn plants into a troublesome situation if you keep the fans on throughout the night. If it's a decent summer night, you may set a schedule to periodically turn on and off the fans.
The best solution is, set a timer to turn off the fans till halfway of the dark cycle. And turn them on again for rest of the dark cycle. This will balance the whole scenario.
Note: We're assuming that you set the dark hours for your plants while it's the night.
How to choose the exhaust/intake fan that best suits your grow room
Here is a simple calculation used by many growers:
Exhaust fan: Potential volumetric capacity of the fan (m³/h) = Volume of the active growing space* (m³) x Air exchange time (hours) x Loss of efficacy.
*Length by width by height of the grow room containing the equipment and the plants
As an example, let's take a basic set up of 1.20 x 2.40 x 2.5 m (7,20 m3) with two 600 W HPS lamps.
Once you have calculated the volume of the growing area you just have to multiply it by the circulating air volume per hour. In indoor set-ups that are not air conditioned or CO2-enriched, where one inch equals 1/minute, this is calculated by multiplying the volume of the growing space by 60 (minutes).
Consider that if you are using a carbon active filter, this will cause a loss of efficiency of about 25 per cent of the potential capacity of the fan. Obviously, this will vary according to the diameter and the condition of the filter as well as to the length of the duct, but in any case 25 per cent is a fairly safe margin. The only thing you need to do is multiply the result by 1.25.
Potential volumetric capacity of the fan (m³/h) = (Volume of the active growing space (m³) x 60) x 1.25, which gives you the minimum volumetric capacity required.
Minimum volumetric capacity required = ((1.2 x 2.4 x 2.5) x 60) x 1.25= 540 m3/h.
The above result is the minimum exhaust capacity of the fan in m3/hour, in this case 540 m3/h. That said, remember that, where possible, it is best to opt for higher performing models.
Going back to the example, you could choose a Max-Fan Pro AC 60/615, which has a 615 m3 exhaust capacity and a 60 mm duct. Alternatively, the RVK 150 Sileo E2 L1 (720 m3/h and 150 mm duct) will give you a greater margin.
Now that you have a clearer idea of how to go about air management in indoor growing, we wish you the best of success with your crops.
