The importance of good air circulation

[Brad104]

I wanted to start a thread about the importance of good air circulation.Its important for your plants to breathe in the carbon dioxide and oxygen and even just for exercise of your plants limbs.If anyone else has anything on this to offer please do.

[Atom]

Agree 100%. My intakes and exhaust run constantly exchanges air. I do set my regular fans on same timer as light though. Give em a small break from breeze. (Accept the tower fan in flower. Didn’t realize when I bought it 3 months ago it would not remain on if power goes out, or if timer switches it.. 🤦‍♂️

[Cannabliss]

Good air movement/circulation can be a huge help.

Fans moving air/making wind to blow young seedlings around can help the stems thicken up. Not a lot of wind, but just enough to make them dance will do.

In flower even more air movement is even more important.

Air needs to be able to circulate above, below, and through the canopy.
The way I draw air through the canopy is to place my exhaust sucking air from the upper right side of the tent & open the lower vent on the left. With enough “CFM” you can exchange the air in the tent multiple timer per minute.

If you want to know how many “CFM” all you have to do is figure out how many square feet are in your space. Length x width x height

 

example: A  2ft x 4ft x 6.5ft tent is 52 sqft total.
a 195 cfm in-line fan can exchange the air in the tent 3.75 times per minute with the vent open on full power.
I happen to have a fan with the same power running in a 2.3ft x 2.3ft x 5.2ft tent

Its on full power exchanging about 7x a minute. I’m flowering an auto & I also have about 8 other individual plants in there with it 😅😅

Ya’ll wanna see it?

 

 

[Somatek]

Solid info and the only thing I had to add was always remember that rated CFM and actual CFM are different as ducting (especially bends), filters and such all reduce the CFM’s.  Generally with tents it doesn’t matter but when calculating the air exchange needed for rooms it gets more complex.  The more resistance on the fan, the lower it’s actual CFM before being reduced by other factors.  Which is why fans should always go on the end of the exhaust system, sucking air through ducting instead of trying to blow it through which drastically reduces CFM.

[Brad104]

Of course we’d love to see it @cannabliss

[Loves2Trim]

Adam I do the same thing, night time is rest time!

[Keith]

I don’t do that but I’d give it a try in veg. I can see the sense in it.  Nature isn’t going to create a constant breeze.

[Somatek]

Always keep in mind we aren’t growing in nature, so it’s more important to consider the botany over what happens in nature.  It’s an easy way to get invested in ideas that have little to no merit.

Although turning circulation fans off at night would reduce the energy and there’s no reason to have them on, although I like to have mine running for an extra half hour to hour before and after lights come on when dew is more likely to form to limit PM growth.

[Keith]

I use an ac infinity t6. I don’t know how I’d be able to dry properly without it.  That’s when I got it last grow and I’m telling you it’s helped so much in controlling my rh and temps during drying.  I’m scared to death of losing an entire harvest to mold.

[Atom]

Ac infinity fans are amazing. I have one In each of my tents. Do you run the booster fans for intake?

[Cannabliss]

Agreed. I have a T4 & I love it.

[Keith]

No I don’t, I wasn’t sure what I needed it for I still need to look into what is for.

[Brad104]

That would be horrible bro,if you were to loose a crop to mold @keith

[Keith]

I’m on my way home from work and they are getting chopped as soon as I get there then I’m gonna take the next 5 hours to cut out all the dead leaves

[Loves2Trim]

How do y’all control your night time temps? My tent during the day runs about 75-77  and about 65-67 at night. I have the SF 6 inch  in-line fan with controller but haven’t found a good way to get the temps a little closer together.

[Atom]

Mine is running about 80-82 with light on and pretty steady 74 lights off. You could try running dehumidifier only at light off period. It raises heat, but of course if your humidity already low may not an option. I don’t think your levels are to bad though, I’ve certainly grown with much higher swings in the past.

You could try running a heater but I wouldn’t put it inside tent. It can be hard to dial in without a central air basically.

On a side note, I despise trimming can we be friends? Lol

• This reply was modified 2 years, 1 month ago by Atom.

[Somatek]

Increasing the ventilation during lights on is the easiest way to keep the temps more equal, having the driver for LED’s outside the grow is another way to reduce it or running a dehumidifier when lights go off will raise the night temp. A 10F drop isn’t horrible but much more and you hit the dew point which makes better conditions for pathogen growth, ideally having them closer together is the goal.

The difference between day and night temps also affects how much the internodes stretch, so controlling the day/night temp differential is another way to manage plant height.

[Keith]

I have a larger size dehumidifier and that usually keeps the area warm enough when lights are off. But soon I think I am going to have to get a heater probably

[Nate]

I really had to up my airflow game last run due to clones brought in with powdery mildew already on them. What I have now is a fan below the canopy (not on yet until they get bigger), a fan above the canopy blowing the opposite direction from the lower one, and then my main exhaust sucks air through the cool tube that has my HID light in it. I just let the intake passively flow through the vents on the bottom opposite where the intake of the exhaust is. My exhaust ducting runs up the stairwell from the basement into the main floor, adding some supplimental heat as a bonus. I would vent to the outside, but I don’t have any windows or doors in the basement, so it’s the best I can do.

[Loves2Trim]

I was thinking my yellowing tips and purple stems may be from temp swings but if you’ve had worse then I’ll keep looking.

[Atom]

A 10 degree swing shouldn’t give you much problems. It’s when it’d like 80 down to 64, you’ll get a spike in humidity and good potential for WPM. Can you throw up a picture? If not me, I’m sure someone can help diagnose. Might be best to start a different topic though. Idk if there’s a diagnosis one but great opportunity to start one if not

[Cannabliss]

It’s usually magnesium deficiency, or could be in the genetics. 9/10 times it’s magnesium from what I’ve run into. A foliar spray is the quickest way to green your leaves back up (given mag deficiency is the cause) purple stems there’s pretty much no bringing back to a nice green once it’s bad, but the new stem growth will be nice & green if treated appropriately.

[Somatek]

N, P and K all express as purple/red petioles first, it’s a very common symptom of nutrient deficiencies not specifically related to Mag.  Mag (or Cal) will always express mid plant first, if it’s the lower petioles showing the issue first then it’s likely N, P, K.

We have to be careful when giving advice about nutrient issues as it’s a complex, nuanced subject and bad advice is confusing and makes the problem worse.  That’s both why I started the thread “help us help you” and why I give very general, vague advice when people give general, vague descriptions about issues.  Without enough info any guess is just as likely to cause more problems then fix existing ones.

[Somatek]

Purple petioles/stems area common sign of nutrient issues, figuring out what the problem is a lot more complex though.

[Cannabliss]

Thanks for stepping in & giving an explanation that actually makes more sense. I noticed as I grew outdoors for the first time that I did get any of the purple stems.
What are you’re thoughts on led playing a role in these purple/reddish expressions?

[Somatek]

I don’t really have enough experience using them and haven’t read any scientific studies looking at nute requirements of different lights/spectrums.  My limited anecdotal experience suggests LED’s need more CalMag to be happy as is commonly suggested.  Normally I don’t use much/any but since switching to LED’s in the veg room I’ve noticed it’s needed now.  Of course I suppose my soil could coincidentally just be depleted as I haven’t had it tested in awhile.

[Keith]

I have a 10ﾟ change in temps between day-and-night sometimes too.

[Loves2Trim]

Tbh I’m willing to kinda throw that issue into every topic since I have yet to identify what causes it. Like this topic for instance, air circulation. My tent sits in an area that’s always about 66 degrees, during day time with lights on it’s about 77 degrees in the grow area. Do I keep my main inline on at night or off because of temp swing? Do they need the circulation at night? I could ask questions all day my friends…

[Atom]

Yes absolutely at night keep inline running. When temps drop humidity will rise and you want air exchanges so you don’t run into powder mildew. I always run intake and exhaust and shut regular fans off. That way there’s still movement but not 24 hours of fan blasting leaves.

[Cannabliss]

<span style=”font-size: 12pt;”>I run my flowers at night to help keep temps down. I’m running 452w at 78F. / 50-55% humidity. Ac running at lights off. Intake from outside at night (lights on) </span>

I have a Bluetooth inkbird in the tent to monitor the numbers and I adjust the intake + extraction accordingly.
If I’m running 78-82F I want my humidity around 60-65%, but in flower it’s better to try & lower it week by week. Getting as low as 30-40% if there’s really thick colas to help avoid mold.
Air flow can help a lot when it comes to keeping mold away. The higher the humidity, the greater the air flow.
Though we try to control our plants environments, unless all the proper equipment is used.. results are going to fluctuate.

I’ve gone through 70F / 68% RH at lights out before in flower. Sometimes multiple days in a row, and had no issues with mold, or rot.
Give those buds space to breathe, and move that air through them.

Be careful if you have high humidity, and a lot of leaf on leaf contact. (Drooping on each other)
<p style=”text-align: left;”>Moisture can transpire & cause powdery mildew to show up. Especially with poor air circulation.</p>

[Somatek]

A couple things nobody have mentioned are negative vs positive pressure in a grow room.  Negative pressure is usually recommended as filters work more efficiently at scrubbing the air clean, positive pressure on the other hand makes it harder for spores to land on plants and more likely to get sucked out instead.  So if you’re legal then it’s something to consider, obviously there’s always security concerns if people can smell your grow.  I’ve been aiming for slight positive air pressure so there isn’t much smell outside (my apartment smells dank, like a den of skunks though) while still mitigating PM risks.

The other option over circulation fans, or used in combination with them is using ducting or a plennum box on the intake at the bottom of the tent to evenly distribute the fresh air and move it through the canopy, which is commonly seen in professional grows and can easily be replicated by building a plywood box to fit inside the bottom of your tent/grow, sealed with silicon that the intake fan blows into.  Combined with the vent fan drawing air through the top of the tent that creates a nice, even distribution of air without having too much which causes too much transpiration stress, forcing stomata to close and limiting photosynthesis.

[Nate]

So with a plenum box, you would branch off ducting from the box? I just did a quick google, and from what I saw, it just looks like a box that will equalize all the pressure in the duct lines attached to it. Am I understanding that correctly? So then I guess you would just even space the ducts throughout the tent to distribute the air? Or would you just have a large box and have vents spaced out on it? Or maybe a grate of some kind? I guess maybe this would be a better option for a tent on the larger side?

Sorry for all questions, I’m just honestly intrigued as I’ve never heard of a plenum box before.

[Somatek]

You never need to apologize for asking questions, the more the better as that means you’re getting the info needed to make sense of things.  Which also helps all the people reading comments but not joining in…

To clarify I was using plennum box in the loosest terms; a chamber to equalize airflow in a ventilation system.  So what I’ve done before in tight spaces which worked well is to make a plywood box (1/4″ ply is plenty) that’ll fit in the grow chamber snuggly that’s a couple inches thick (usually 4-6″ to match the intake fan) with silicon sealing all the edges and where the fan connects.  Then I drill a bunch of holes (1/4-1/2″ is plenty, or a combination) until I have and even airflow coming out the top of the box as long as the fan has enough CFM to create even air pressure in the “plennum” box.  Then pots/saucers can sit on spacers so no holes are blocked and you’ll have good, even air circulation without needing additional oscillating fans if the space is really tight.  It really works wonderfully in a vertical system where the plants/pots are off the ground, which is when I first experimented with it and I’m debating doing something similar in my current grow by making some duct work that’ll reduce my 6″ intake down to 2″ pvc tubes that are perforated on top which run through the flowering area for air circulation.

[Nate]

Damn, that’s genius. I was planning on having my pots on top of a plastic pallet that I got at work. I had to cut off one end of it to fit in my 3×3, so it isn’t pretty, but it should work to keep my pots off the cold concrete. I’ll have to look into that for the next run if I can get the money for a second fan by then.

[Somatek]

A plastic pallet covered in thin, rigid plastic would be even better as it’s more inert then wood and would be easy to convert once you have a second fan.

[Nate]

For sure, I’ll look into sourcing sheets of plexiglass and see if it would be feasible to do it once I get around to getting the second fan. When I do end up getting around to it, I’ll try to remember to do a step by step guide on here.

[Somatek]

Do you need to use plexiglass or would something like this be enough to create a air tight box?

I use to use it when I played TTRPG’s (warhammer 40k, warmahordes, etc) for building model buildings and it popped to mind as a cheap rigid plastic covering.

• This reply was modified 2 years, 1 month ago by Somatek.

[Nate]

That’s not a bad option actually. Originally I was thinking it would need to be fairly thick, assuming it would need to bear weight, but now that you mention it, the pallet would be responsible for the weight, and the plastic would only need to hold air. It would definitely be more cost effective, that’s for sure.

[Somatek]

Exactly my thoughts, you already have a solid structure that’s way over spec, all you need is a covering for it.  In a pinch you could even just wrap it in 6mm poly but that’d need to be replace as holes get punched into it.

[Nate]

I think maybe this one might be a better option, as I’d much rather cut down on piece for the top and bottom, rather than gluing together a bunch of 20 cm x 25 cm sheets. Pretty much the same idea though.

[Somatek]

Find a bigger supplier of plasticard, that was literally just the first link I clicked on put it’s made in all sorts of sizes.

[Nate]

Oops, I messed up the link. here’s what i meant to link.

https://www.amazon.ca/Large-Clear-Plastic-Sheets-Terephthalate/dp/B08DWMVSW1/ref=sr_1_7?crid=21C9LW1CG63G&keywords=large+abs+sheets&qid=1665283529&qu=eyJxc2MiOiIxLjkxIiwicXNhIjoiMC4wMCIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=large+abs+sheets%2Caps%2C90&sr=8-7

• This reply was modified 2 years, 1 month ago by Nate. Reason: For some reason the amazon link posted as a kindle link??

[Somatek]

There ya go, that’ll do nicely.  You may want to check what it off gases as some products can be toxic to plants and I don’t know that material specifically.

[Nate]

Yeah I’ll look into the exact materials more once I get an intake fan. One step at a time lol

[Brad104]

I hope you have a good connection @nate with the plexiglass, for it’s very expensive.I think you could do better purchasing a new tent than building one out of plexiglass.I don’t know you may have something else in mind and know something I don’t,but around here it’s super expensive bro

• This reply was modified 2 years, 1 month ago by Brad104.

[Brad104]

Glad to see all the interesting things every ones discussion’s.I knew that this would be a interesting thread

[Loves2Trim]

All great input. Thank you everyone. I think im gonna move some stuff a4ound and go for positive pressure in room. I think that would be easy to achieve.

[Somatek]

With infinity fans it’s dead easy as you just adjust the intake/exhaust fans until you see the tent puffing out slightly.  Which is my idea to create a clean area for tissue cultures, have a fan blasting air into a tent through a hepa filter and then basically treat it like a giant clean box for growing mushrooms lol.

[Loves2Trim]

Dude that is genius, I need another tent now!

[Brad104]

I can’t wait to get me a tent and try it out soon!

[Somatek]

works in rooms just as well as the chamber doesn’t matter as much as the principles involved.

[Author]

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