Fan usage in greenhouse

Hi there ICMag,

Last year we made one of many mistakes in our greenhouses, by not having any fans at all. It might've not been such a problem if our greenhouses were much bigger than our plants, and we didn't have so many moist/humid/rainy days during flowering. We ended up with lots of bud rot and PM. This year we were very pro-active with fans with hopes of avoiding that this time, and had oscillating fans in each section of each greenhouse. For a while it seemed amazing. It kept the temps down and the air fresh. We soon realized that the vegging plants hated it once they grew tall enough, and that everywhere that the fans were blowing on the plants, growth was greatly reduced, and it was also fuckin up the leaves. So now we just have fans running along the top of each house, all in one direction, cycling fresh air in and old air out. That seems to be working well. But as we approach week 3-4 of flowering, we are worried that there will not be enough air moving around the plants. Are the exchange fans going to be enough to reduce moisture? We have them running 24hrs a day. What do some of you guys do for greenhouse fans? If we have the fans oscillating during flower, will it have less of an effect on the buds than it did on the veg leaves? We are considering have them oscillate again and in turn blow around the tops of the plants. I'm going to browse around and see what other people do but I wanted to get some answers if possible. Cheers.

I wanted to mention that these are big greenhouses. 50' x 20' x 15'

the key to growing in a gh in less than optimal climate , is strain selection . you cannot count on buying seeds that are mold resistant , you have to test a heap of strains in your own environment and find what works best .( i tested over 40 strains to achieve this )

so what i,m saying is , get your ventilation dialled in by all means , but it doesn't mean shit if your haven't got the right strains in there

you may want to re-think your airflow paradigm. more fans isn't your answer, you need to exhaust what you have more efficiently.

Do you have roll up sides? I have a 48 long by 20 wide by 12 high and have 4 foot roll ups on either side. this keeps the natural breeze blowing through. I also have a 24 inch commercial chicken barn fan at one end and a 32 inch louver at the other. i may switch to a big 48 inch, they move so much more air.

even with the front door open it is very hot in there, over 80.

you may consider roof vents, like the ones that run the length of the greenhouse, 4 foot wide i believe. my quote with a chain opener is 2K. this is the best way to vent heat and moisture.

you may also consider putting in roll up sides to the peak. i am keeping my 4 foot roll up but putting another one from 4 feet to the peak, so i have two on one side, being the dominant sun side.

growing behind plastic is ok but for boffo results you want to roll that plastic up and grow in the sun...except for windy days when you only roll it up a bit.

i hope this helps.

Hey thanks for the reply. All of our houses have roll up sides and they are rolled up 24/7 to allow breezes (sometimes theyre strong enough to knock plants over that have 3 layers of trellis!) to pass through. We have oscillating fans every 15 feet, locked in non oscillating mode, all pointing the same direction, to suck outside air in and to push inside air out. 4 or 5 per house. A couple of them have can fans instead. These are all near peak of the house heightwise, so that they arent blowing plants over. So it seems like everything should be aerated enough, my only concerns are 1. There isnt enough air blowing around the plants themselves because they are lined along the sides, with a small walkway in the middle, the fans dont toouch them. 2. On those few rainy days or weeks we may have, when we might want to drop the sides, enough moisture will collect and induce mold or mildew.

Do you have double layer plastic with a fan separating the layers?
I have a 30x48x16 at the peak greenhouse.. By buddy has the same but chose a single layer of plastic over the top. He has massive condensation and humidity problems while mine stays dry.
I also have a 48" fan, two 24" circulating fans and a 4' X 8' intake above the front doors.
I rarely if ever get any dew or wetness on my greenhouse plants!

petert said:

Do you have double layer plastic with a fan separating the layers?
I have a 30x48x16 at the peak greenhouse.. By buddy has the same but chose a single layer of plastic over the top. He has massive condensation and humidity problems while mine stays dry.
I also have a 48" fan, two 24" circulating fans and a 4' X 8' intake above the front doors.
I rarely if ever get any dew or wetness on my greenhouse plants!

Click to expand...

I've been pondering this idea myself.
My problem is temps are diving here and far to many overcast days and I have 5 to 6 weeks to go. Cool temps and condensation.
I've got a little wee 10ft x 16 x 10high greenhouse framed with 2x4 and greenhouse plastic. I put 2 x 1000 watt electric heaters but it's barely cutting it and only reaching 17Celcius daytime on the cloudy days. We'll see first frost here by the 10th guaranteed.
So I'm thinking of getting another layer of plastic and stapling to the inside of the 2x4 frame , leaving a 1 3/4 inch air gap between the sheets and I could shoot hot air into it with one of those heaters.........
wonder if it's worth the trouble , would love some input

Daaaaamn petert you're smart. No, ours are really simple, just 2x4's and a single layer of plastic. The fans just run along the peak from one end to the other. I would think that having all the sides up would allow enough air circulation with wind. Explain to me this dual layer plastic concept. The fans in between the layers? I'm having trouble making sense of that.

Cheers

First layer is pulled tighter than the second layer..I have a small 4" fan mounted inside the of the greenhouse just above the 2x6 that the wiggle wire breakers are mounted on.. The fan has a beaker that clamps on to the first layer and a small hole is cut into the bottom layer and the fan blows air I between the two layers. I'm in the northern Cascades of Oregon and it gets cold.. These days we can get into the upper 70's to mid 80's in Sept and the lows get into the lower 40's so dew and condensation happens.. But my greenhouse stays dry.. If the plants get damp from dew I turn on my circulating fans. They are mounted on Perlins about 10' up.
If that's not clear I can shoot a couple pics

oui oui des photos svp

Can you post a photo?

Very interesting thread! I would love seeing some photos of this double layer concept as well.

Talking about the fans pointed directly to the leaves, I've seen the same behaviour over the 3-4th week on my plants too, they seem not to grow as good as in a "common" wind circumstance.

Hope you guys find a good strain to hold out those problems.

yea petert , lets see it.

im kinda doing the same setup, farmtek series 500 20'x60'x16' w/double poly . four big oscilating fans at 10'hi and every 20', and four floor fans on floor opposing end of, the intake louvers 2 ( 30"x60")schaffer with 3 schaffer 24'' 5kcfm on the end wall pulling it all. with 4'side wall if its not to windy. had to throw 2 (5kcfm swamp coolers to cool it ofF)