Struggling to get RH below 60-70%. Is it detrimental to the grow?

[FlooK]

I'm aware of the VPD chart and I know I should have a lower humidity but with the rising energy costs and how poorly my house is insulated I don't think its possible to bring it down without spending a small fortune. 

 

The question is, is a high humidity going to seriously lower the quality of my grow? The tent sits around 28/29/30c and is around 60 to 70% RH. I have 3 fans in there so the airflow is pretty good. 

 

Any info greatly appreciated

[ratdog]

it's fine for veg and early flower, up to about week 5

 

then you want to deal with it, i find adding a heater and upping the extraction really helps

[FlooK]

Just now, ratdog said:

it's fine for veg and early flower, up to about week 5

 

then you want to deal with it, i find adding a heater and upping the extraction really helps

 

Yeah im week 5/6 now so starting to give it more thought. I'd considered increasing the speed of the extraction fan but the lung room is 69% RH now and the tent is 70% RH so doubt it would alter much. I'm also around 30c so can't really afford to increase the temps anymore. Not sure what else I can do

[CDF20]

1 minute ago, FlooK said:

 

Yeah im week 5/6 now so starting to give it more thought. I'd considered increasing the speed of the extraction fan but the lung room is 69% RH now and the tent is 70% RH so doubt it would alter much. I'm also around 30c so can't really afford to increase the temps anymore. Not sure what else I can do

I have same problem as you mate. I did this: defoliated bottom then used two 9" fans on floor opposite to each other and facing the walls (if you go for this then make sure your fans not facing intakes otherwise your room will stink). Two 6" inches on top same opposite way to each other. My RH was 60%-68% and managed not to catch botrytis.

The best solution is split units AIR CON - dear but worth it. DEFO will install one in spring time ... 

 

Good luck and do not worry much all you need is good airflow inside the tent as botrytis loves stale (no movement) air ... 

[FlooK]

2 minutes ago, CDF20 said:

I have same problem as you mate. I did this: defoliated bottom then used two 9" fans on floor opposite to each other and facing the walls (if you go for this then make sure your fans not facing intakes otherwise your room will stink). Two 6" inches on top same opposite way to each other. My RH was 60%-68% and managed not to catch botrytis.

The best solution is split units AIR CON - dear but worth it. DEFO will install one in spring time ... 

 

Good luck and do not worry much all you need is good airflow inside the tent as botrytis loves stale (no movement) air ... 

Nice one for the info mate ill give that a try. Out of interest why do you point the fans towards the walls? I would have thought it would be better to keep the air moving in the centre near where leaves and buds etc are touching. Here's a pic of my canopy:

 

[GSZZ]

Bud rot is caused by cell damage, guttation and dew point, not by high humidity. Plants don't transpire at night, they close their stomata - if the pots are wet, or something is causing convection (warm roots cold tops) the water potential of the roots becomes lower than the soil and water begins to move up the plant, but because the stomata are closed it has to come out of somewhere - so it comes out of the glands along the leaf tip edges and/or bursts the cells to escape, these actions let fungal spores in and the circumstance surrounding the entry, means its the perfect conditions for it to do maximum damage in a short amount of time (wet, warm, dark, sugars etc). 

 

The quickest and easiest way to cure the issue is to use an online dew point calculator and work out what the dew point is, and then make sure your night time temps are well above that. Its worth remembering that the quicker and larger the temp drop, the worse it will be. 

[CDF20]

2 minutes ago, FlooK said:

Out of interest why do you point the fans towards the walls?

I've read somewhere that it's better not to point fans on buds or plants and instead do it on walls as its spreads air better and doesn't stress the buds/plants. I took this advice and it did work BUT I bet EXPERIENCED growers here can clarify if it's right or bro science. 
 

[CDF20]

1 minute ago, GSZZ said:

Its worth remembering that the quicker and larger the temp drop, the worse it will be. 

Thanks mate. That's why I didn't get bud rot as my temps fluctuation was 3 degrees only (28C lights off, 31C/31,5C lights on). 

[FlooK]

18 hours ago, GSZZ said:

Bud rot is caused by cell damage, guttation and dew point, not by high humidity. Plants don't transpire at night, they close their stomata - if the pots are wet, or something is causing convection (warm roots cold tops) the water potential of the roots becomes lower than the soil and water begins to move up the plant, but because the stomata are closed it has to come out of somewhere - so it comes out of the glands along the leaf tip edges and/or bursts the cells to escape, these actions let fungal spores in and the circumstance surrounding the entry, means its the perfect conditions for it to do maximum damage in a short amount of time (wet, warm, dark, sugars etc). 

 

The quickest and easiest way to cure the issue is to use an online dew point calculator and work out what the dew point is, and then make sure your night time temps are well above that. Its worth remembering that the quicker and larger the temp drop, the worse it will be. 

Appreciate the detailed response. Sadly my temp swings are pretty large. 30c or so during lights on and ~20c during lights off. According to the calculator it says I need to keep dark temps above 24c or so to be safe. I guess my options are either add some heating during lights out or buy a quality dehumidifier for the lung room. Both options are pretty costly. Fuck. 

 

Edit: I've played around with the calculator a little bit, if my tent is 28c during lights on and RH is 60%, it can safely drop to 19.5c during lights off and there should be no issues with dew. Seems pretty reasonable I'm not too far away.

Edited September 13, 2022 by FlooK

[FlooK]

17 hours ago, CDF20 said:

Thanks mate. That's why I didn't get bud rot as my temps fluctuation was 3 degrees only (28C lights off, 31C/31,5C lights on). 

 

How are you keeping the tent at 28c while the lights are off? 

[Military Grade]

My Meaco 20L dehumidifier works wonders and is cheap to run.

[Military Grade]

18 hours ago, CDF20 said:

Thanks mate. That's why I didn't get bud rot as my temps fluctuation was 3 degrees only (28C lights off, 31C/31,5C lights on). 

It's fluctuations of more than 10%RH that can causes bud rot not the temps if RH is within a reasonable %, almost all on my first 6 grows would swing from 18c to 29c lights off/on and never had bud rot in that time.

If you have the RH in order dew pont won't been an issue. You have to go very cold to make 50%RH to be a dew point.

Edited September 13, 2022 by Military Grade

[CDF20]

1 hour ago, FlooK said:

 

How are you keeping the tent at 28c while the lights are off? 

 My MEACO Arete 25L is ON all the time to keep RH more or less stable and also keeps high temps, another thing I had a grow during heat waves (3 weeks it was in the part where I live). 

 

 

1 hour ago, Military Grade said:

My Meaco 20L dehumidifier works wonders and is cheap to run.

Agree, love MEACO products. Got two one Arete another Zambezi for cold days ... Bought MeacoFan 360 Personal Air Circulator today and HOPE it will be run quiter than my 9" STATUS fan (good cheap and reliable though).

 

1 hour ago, Military Grade said:

It's fluctuations of more than 10%RH that can causes bud rot not the temps if RH is within a reasonable %, almost all on my first 6 grows would swing from 18c to 29c lights off/on and never had bud rot in that time.

If you have the RH in order dew pont won't been an issue. You have to go very cold to make 50%RH to be a dew point.

 

Thanks, mate. I need to read more about dew point as it looks like I was a lucky that all these factors (dew point, acceptable RH fluctuations and temps) were spot on.

 

Seems like high RH is no problem anymore! GREAT!

 

 

Checked my AC infinty APP and my RH MAX 60% and MIN 57% with AVERAGE 58.8% . These datas from last week.
Was sure there was a DEW POINT in this app but can`t find it now. 

Edited September 13, 2022 by CDF20
Grammar