question about how long to leave fans on???

[richirich_99]

I know that i have read something a while back about your fans that are used for air circulation inside you grow cab being left on for either 24hrs or turn off with the light schedule and how one may be better than the other. I was wondering what you guys think, and do you run your fans in your cab 24/0 or with the light schedule?

I think that if you have your exhaust running 24/0 so that there is still being replaced inside the cab, but there is no need for small fans inside to be on as well as long as you have negative pressure.

Whats your opinions? Hope this sparks some discussion.

 

[Vegan]

i only circulate the air in my GR once an hour-- 24/7 just enough to shiver the plants a bit..somethin about stimulating cells in the stalk?..i dont want em bending over and breaking with those big ass colas--------mayby and old wives tale..
now if you doin a SOG or SCROG that prolly isnt a worry



if I had the room I would prolly use a nice big oscillating fan 24/7

 

[Maj.PotHead]

all fans run 24/7 keep proper air circulation going at all time and helps to prevent powdery milder or mold to form on dense ass nugs. i've found ocilating fans are my enemy i leave then stationary and adjust one way or another. you'll find that some time just by moving a fan 1 inch can drop your temps 2-4 degrees

 

[Charlie_Citrine]

I run it 24/0.
Humidity rises a bit when the lights go off, and I run a scrubber too, so I need it to run all the time...nothing hurricane-like, just a constant inflow ---> outflow thing going on.

 

[Amon]

Air circulation is a must, especially when lights are on. and there is nothing wrong with really good air movement. Lights off is a different story IMHO>

With running your exhaust fan, do you have passive holes setup in the bottom of the grow cabinet with exhaust fan at top-(hot air rises). The passive holes will make huge difference and always have 2x's the size hole/holes for passive as you do for exhaust. Ex: I run a 449 cfm exhaust fan thru a 6" system. I have 2/6" passive holes. The passive holes are at the base near the window A/C unit side and, draw in fresh cool air. You know your negative pressure is perfect when just before you close the door it sucks it out of your hand and closes it. hehe.

Rule of thumb is this. You want all the leaf material in the grow room to flutter lightly. And if the bud's get so big the fan is gonna break them over, tie the suckers up, but leave the fans' on those big buds to avoid bud rot, mildew etc etc etc. It keeps humidity down during flowering, especially if you water at night right when lights go off. Getting your humidity down to 25/30% during flowering will increase yields too.

OH, any reason why your using 24/0 instead of 18/6. I only use 24/0 with clones until rooted. And seedlings for 1st week. After that, 18/6 to allow plants to stay shorted, less stretch and pre-flower much quicker. peace

 

[K.J]

Air circulation in a closed cab is a must 24/7, in my opinion, but I guess it all depends on the local situation. If I were to turn off the exhaust fan, temps would go up and the wonderful aroma's of flowering cannabis would begin leaking out of every crack and crevice in the box. So yeah, that fan stays on 24/7. The oscillating fan in our flower room goes on and off with the lights.

 

[richirich_99]

WOW thanks for the quick responses! I didnt think about leaving the fans on to help fight powdery mildew and mites. I think im going to keep mine on 24 hrs now. I have had problems off and on with mites and go a bad case of powdery mildew in my last cab in mid flowering. i have gotten that taken care of, but want to play it safe. I leave my veg on 18/6, not 24/0 sorry Amon if i confused you. I have clones and rooted and not rooted and my mothers all under 18/6.

Im not too worried about humidity where i live during the summer months, i have about 10-30% RH in my cab at almost all times. Doesnt low RH help stimulate more resin production?
Thanks for all the great input!

 

[richirich_99]

KJ- you just beat me, i was writing that while you posted. Do you ever have any mite or powdery mildew problems with the oscilating fan off with the lights? I have my exhaust on 24 hrs as well, have too because one fan is used to exhaust my entire NGB cab.

 

[Moldy Dreads]

Do you ever have any mite or powdery mildew problems with the oscilating fan off with the lights? I have my exhaust on 24 hrs as well, have too because one fan is used to exhaust my entire NGB cab

Mites won't be deterred by a fan, once they invade the room, you're screwed, but PM can be deterred a bit by air circulation but only to a certain point IME. If PM is already on the clones and extra humidity will make that flourish, even fans can't deter it if the spores are already on plants and the humidity rises or there are open containers with water or the medium is always wet...

 

[richirich_99]

thanks for the head up about the fans and mites, i was mistaken. Luckily i have gotten rid of the mites for the most part, i still find a few eggs here and there and spary the plants in veg with neem at least once before they go into flower. i used neem for the PM too and it seemed to get rid of it, it hasnt shown up on any other plants.

 

[Cracky]

Fans on at all times except;
When the temps are cool (winter) and the seedlings are fragile, no fans until they are strong enough and then only when the lights are on.

Definetly lots of air movement when in bloom to prevent mold and bud rot.

 

[10k]

To echo what a few of you are saying, and elaborate on why it's critical...

This is a topic that can't be stressed enough and IMNSHO number one cause of bud rot and mildew.

The most important time to keep the air circulating and exhausting is during lights off. When plants are in the dark is when they transpire a lot of moisture.
In an enclosed grow tightly packed with plants, and even more so in a hydroponic grow, this moisture will build up on the foliage and in the buds keeping them wet, and even back feeding the plants like a foliar spray. This foliar back feeding effect isn't good for nutrient uptake for one thing, but of more importance is that such a soaking wet condition is a prime situation for a nasty case of bud rot and pm.

So it is very important to have some circulation to keep the air moving and help get that transpired wetness evaporated off the leaves and out of those precious buds. For this reason, it's also very important to have exhaust running to pull out all that evaporated excessive humidity which in turn will aid the evaporation.

If you have it, dehumidifying is also very helpful in an enclosed space at night, but it will be somewhat useless if the air isn't moving in, around and through the canopy to help that transpiration evaporate away from the plants.

Outdoors plants enjoy mother natures breeze to accompany the transpiration...
Indoors we need to simulate the same effect... unless you like poisonous grey gunky moldy buds and lung disease !

 

[richirich_99]

thanks for all the responses.
10K- thanks for the info about the transpiration and the fans, that makes complete sense. you have me convinced to keep em on 24/0. I already changed them today to 24/0.