Under canopy humidity

[Damien102]

Hi all, hope I'm asking this in the right place.
Firstly I'm a newbie, this is my 3rd grow. I got 2 auto's in early flower in a 2x2x4 tent under a 200w Q-Board. I have somewhat of an RH problem (I think). I'm SCROGing BTW. Above canopy is 77 degrees and 45% rh (lights on) BUT I have another hydrometer below the canopy clipped to the top of one of the (fabric) pots. That one is reading 68 degrees and 61% rh. Is this typical? Is there a way bring that 61% down and still keep the top dialed in? If it can't be evened out could this hurt the entire plant or will it just make the bottom non-yielding or trash?
I googled it but nothing addressed my specific issue.
Thanks in advance for any advice, fixes or clarification

 

[Bill284]

Hi all, hope I'm asking this in the right place.
Firstly I'm a newbie, this is my 3rd grow. I got 2 auto's in early flower in a 2x2x4 tent under a 200w Q-Board. I have somewhat of an RH problem (I think). I'm SCROGing BTW. Above canopy is 77 degrees and 45% rh (lights on) BUT I have another hydrometer below the canopy clipped to the top of one of the (fabric) pots. That one is reading 68 degrees and 61% rh. Is this typical? Is there a way bring that 61% down and still keep the top dialed in? If it can't be evened out could this hurt the entire plant or will it just make the bottom non-yielding or trash?
I googled it but nothing addressed my specific issue.
Thanks in advance for any advice, fixes or clarification

Hey Damien
I keep fans going below the canopy mixing with the air above.
Keeps the entire room at a constant rh usually of my choosing
But consistent airflow , warm temps and low rh are important during flower.
I also clean everything under the skirt out after stretch, which helps.
Take care.
Talk soon.


Stay safe
Bill284

 

[Trump]

Hey Damien,

You said you're scrogging. Do you have a picture of the scrog? Without seeing the condition of your canopy it sounds like you need to do a defoliation for better air circulation. As @Bill284 mentioned, you should have an air circulator moving air under the canopy alonbg with another moving air above the canopy. If your canopy is correctly defoliated that air should mix with your above canopy air and equalize your RH. Temp will differ a bit but, IMO, your lights on temps are a bit low. I like to run my grow at 80° - 82° and 55% - 60% RH in flower up to the last few weeks where I'll lower the temp to 75° - 78° and 45% - 55%.

In ScrOG, typically, you lollipop everything under the net line. Did you do that? Lack of air circulation can help mold and other diseases like PM get a foothold in your garden

 

[SmokingWings]

BUT I have another hydrometer below the canopy clipped to the top of one of the (fabric) pots. That one is reading 68 degrees and 61% rh. Is this typical? Is there a way bring that 61% down and still keep the top dialed in?

The leaves give off water vapor plus more is evaporating from the soil surface. If the canopy is thick enough it becomes trapped there unless there is a good airflow.

What @Trump mentions in his msg. Often enough some pruning under the net or screen is all that is needed to keep the air flow moving with the average set-up. The leaves on the small stems there will not produce much once in flower so now is a good time to start clearing it out.

 

[Damien102]

Hey Damien,

You said you're scrogging. Do you have a picture of the scrog? Without seeing the condition of your canopy it sounds like you need to do a defoliation for better air circulation. As @Bill284 mentioned, you should have an air circulator moving air under the canopy alonbg with another moving air above the canopy. If your canopy is correctly defoliated that air should mix with your above canopy air and equalize your RH. Temp will differ a bit but, IMO, your lights on temps are a bit low. I like to run my grow at 80° - 82° and 55% - 60% RH in flower up to the last few weeks where I'll lower the temp to 75° - 78° and 45% - 55%.

In ScrOG, typically, you lollipop everything under the net line. Did you do that? Lack of air circulation can help mold and other diseases like PM get a foothold in your garden

No doubt I got too thick of a canopy. I got anxious and I put the net to low to soon. I I defoliate by pinching off a couple leaves from the top, but those because they block light to lower bud sites.
Its a very tight space, (2x2 with 2, 5gal fabric pots) so I've been hesitant to put a fan at the bottom for heat of getting dry spots inside the fabric pots where the fan blows on them, But I guess that's my only option

Hey Damien,

You said you're scrogging. Do you have a picture of the scrog? Without seeing the condition of your canopy it sounds like you need to do a defoliation for better air circulation. As @Bill284 mentioned, you should have an air circulator moving air under the canopy alonbg with another moving air above the canopy. If your canopy is correctly defoliated that air should mix with your above canopy air and equalize your RH. Temp will differ a bit but, IMO, your lights on temps are a bit low. I like to run my grow at 80° - 82° and 55% - 60% RH in flower up to the last few weeks where I'll lower the temp to 75° - 78° and 45% - 55%.

In ScrOG, typically, you lollipop everything under the net line. Did you do that? Lack of air circulation can help mold and other diseases like PM get a foothold in your garden

couple pics on my last post.... I kind of screwed the SCROG. I got anxious and put up the net to low to soon

 

[Damien102]

No doubt I got too thick of a canopy. I got anxious and I put the net to low to soon. I I defoliate by pinching off a couple leaves from the top, but those because they block light to lower bud sites.
Its a very tight space, (2x2 with 2, 5gal fabric pots) so I've been hesitant to put a fan at the bottom for heat of getting dry spots inside the fabric pots where the fan blows on them, But I guess that's my only option

couple pics on my last post.... I kind of screwed the SCROG. I got anxious and put up the net to low to soon

Update Just put in a fan bottom of canopy now 72F & 45 rh. I'm prolly gong to have to put twice as much water on the side where that fan blows on the fabric pots. It's going to dry them out for sure

 

[Trump]

I would just clear out the middle of the plant of most of the water leaves. It'll open the plant for better air flow and allow more light to penetrate deeper into the plant so that you eliminate the larf.

Remove the bottom fan. You're right. It's going to make dry spots in your soil. You should have enough air flow in the tent with the fan you have mounted above. Try and raise the temp in the tent a few more degrees if you can. Shoot for 80°/55%.

I have a 2 x 2 and a 5 x 5 going.

2x2 Mystery ScrOG

Now that I have another light to supplement the 5 x 5, I decided I would take the ViparSpectra XS1500 Pro that I was going to use for supplemental and put it back into my 2 x 2 tester. I'm not testing anything at the moment so I thought I'd have a little fun and do a mini ScrOG! When I trim down...

www.420magazine.com

Trump Growing Jan6 OG

Not really. Just thought it would be funny if there was a strain like that to grow!!🤣 Growing some Florida Strawberry clones I clipped off my mother. 11/15/2023 Temp - 81.5* Humidity - 58% VPD - 1.59 kPa DLI - 41 Leaf Temp - 80* Netted the girls as they were getting too tall and the branches...

www.420magazine.com

 

[OneEyedWilly]

Hey Damien,

You said you're scrogging. Do you have a picture of the scrog? Without seeing the condition of your canopy it sounds like you need to do a defoliation for better air circulation. As @Bill284 mentioned, you should have an air circulator moving air under the canopy alonbg with another moving air above the canopy. If your canopy is correctly defoliated that air should mix with your above canopy air and equalize your RH. Temp will differ a bit but, IMO, your lights on temps are a bit low. I like to run my grow at 80° - 82° and 55% - 60% RH in flower up to the last few weeks where I'll lower the temp to 75° - 78° and 45% - 55%.

In ScrOG, typically, you lollipop everything under the net line. Did you do that? Lack of air circulation can help mold and other diseases like PM get a foothold in your garden

Hi Trumph...I've been following the following guide (Perfect humidity levels for cannabis plants fluctuate) for RH during flowering where it says that when you BEGIN flowering, you should have your RH at 40-50%.

I was just wondering if there is a definitive guide for RH during the 8 weeks of flowering, because I see many posts, including yours here, on many different sites citing varying ranges of ideal RH during flowering.

Thanks in advance.

 

[Bill284]

Hi Trumph...I've been following the following guide (Perfect humidity levels for cannabis plants fluctuate) for RH during flowering where it says that when you BEGIN flowering, you should have your RH at 40-50%.

I was just wondering if there is a definitive guide for RH during the 8 weeks of flowering, because I see many posts, including yours here, on many different sites citing varying ranges of ideal RH during flowering.

Thanks in advance.

I like around 60 rh week one and around 5 by week 8.
Gradually bringing it down.
Seems to work well.
Just 2 cents.
Hope your doing well.


Stay safe
Bill284

 

[Trump]

I like around 60 rh week one and around 5 by week 8.
Gradually bringing it down.
Seems to work well.
Just 2 cents.
Hope your doing well.


Stay safe
Bill284

5% RH seems rather low no? I'm guessing you meant 50%?

Hi Trumph...I've been following the following guide (Perfect humidity levels for cannabis plants fluctuate) for RH during flowering where it says that when you BEGIN flowering, you should have your RH at 40-50%.

I was just wondering if there is a definitive guide for RH during the 8 weeks of flowering, because I see many posts, including yours here, on many different sites citing varying ranges of ideal RH during flowering.

Thanks in advance.

Everyone has there own way but starting flower at 40% seems awfully low to me. My fear would be that the leaf stomata closes and the plant stops transpiring because it's trying to hold moisture in. I would do as @Bill284 does and start around 60%.

I usually let it hover around there for the first 5 - 6 weeks of flower then start to gradually drop RH to around 45% the last few weeks.

As far as plant response I don't think there is a huge difference in regard to the humidity difference. I think most of the reason many like to get it really low like that is to avoid any mildew or mold along with helping the flower in its last push to make terpenes and essential oils in flower.

I wouldn't go any lower than 45% RH.

 

[Bill284]

5% RH seems rather low no? I'm guessing you meant 50%?



Everyone has there own way but starting flower at 40% seems awfully low to me. My fear would be that the leaf stomata closes and the plant stops transpiring because it's trying to hold moisture in. I would do as @Bill284 does and start around 60%.

I usually let it hover around there for the first 5 - 6 weeks of flower then start to gradually drop RH to around 45% the last few weeks.

As far as plant response I don't think there is a huge difference in regard to the humidity difference. I think most of the reason many like to get it really low like that is to avoid any mildew or mold along with helping the flower in its last push to make terpenes and essential oils in flower.

I wouldn't go any lower than 45% RH.

So sorry, I just had a heart attack.
5 was supposed to be 50 @Trump

@OneEyedWilly have you seen a vpd chard?

Stay safe
Bill284

 

[OneEyedWilly]

5% RH seems rather low no? I'm guessing you meant 50%?



Everyone has there own way but starting flower at 40% seems awfully low to me. My fear would be that the leaf stomata closes and the plant stops transpiring because it's trying to hold moisture in. I would do as @Bill284 does and start around 60%.

I usually let it hover around there for the first 5 - 6 weeks of flower then start to gradually drop RH to around 45% the last few weeks.

As far as plant response I don't think there is a huge difference in regard to the humidity difference. I think most of the reason many like to get it really low like that is to avoid any mildew or mold along with helping the flower in its last push to make terpenes and essential oils in flower.

I wouldn't go any lower than 45% RH.

And that would explain the dismal harvest I got. I followed their recommendations of keeping the RH between 40-50, and kept it precisely @45%…Net result…Marbles instead of Nuggets.

 

[OneEyedWilly]

So sorry, I just had a heart attack.
5 was supposed to be 50 @Trump

@OneEyedWilly have you seen a vpd chard?

Stay safe
Bill284

Thanks @Bill284…I’ll print a copy off and keep it on my tent

 

[Trump]

Thanks @Bill284…I’ll print a copy off and keep it on my tent

Keep in mind that using VPD charts should include using the leaf temperature as part of the equation. You need to use the differential of your air temp and your leaf temp to arrive at the correct VPD. You can use a laser thermometer to get an average leaf temperature by testing different areas of the canopy. This means your VPD will change as your air and leaf temp differentials change.

I use the VPD charts from Dimlux. They have them in graduating order of temp differential.

VPD calculator

Vapor Pressure Deficit VPD Calculator - Dimlux Lighting - The Best Grow Lights

Vapor Pressure DeficitCalculator Calculate both Room VPD and Leaf VPD automatically Just enter the value below to generate the VPD values for your room and your plants. You’ll need to know the room’s temperature, relative humidity, and the plant’s temperature. We recommend calibrating your...

www.dimluxlighting.com

VPD charts with differentials are at the bottom of the page.

 

[Wastei]

Keep in mind that using VPD charts should include using the leaf temperature as part of the equation. You need to use the differential of your air temp and your leaf temp to arrive at the correct VPD. You can use a laser thermometer to get an average leaf temperature by testing different areas of the canopy. This means your VPD will change as your air and leaf temp differentials change.

I use the VPD charts from Dimlux. They have them in graduating order of temp differential.

VPD calculator

Vapor Pressure Deficit VPD Calculator - Dimlux Lighting - The Best Grow Lights

Vapor Pressure DeficitCalculator Calculate both Room VPD and Leaf VPD automatically Just enter the value below to generate the VPD values for your room and your plants. You’ll need to know the room’s temperature, relative humidity, and the plant’s temperature. We recommend calibrating your...

www.dimluxlighting.com

VPD charts with differentials are at the bottom of the page.

The IR meters suck pretty hard and are not in any way accurate and may be 5 degrees of from actual leaf temperature. You need a real FLIR camera to accurately measure leaf temp.

IR meters are for cooking and things that doesn't require pin point accuracy.

 

[Bill284]

Keep in mind that using VPD charts should include using the leaf temperature as part of the equation. You need to use the differential of your air temp and your leaf temp to arrive at the correct VPD. You can use a laser thermometer to get an average leaf temperature by testing different areas of the canopy. This means your VPD will change as your air and leaf temp differentials change.

I use the VPD charts from Dimlux. They have them in graduating order of temp differential.

VPD calculator

Vapor Pressure Deficit VPD Calculator - Dimlux Lighting - The Best Grow Lights

Vapor Pressure DeficitCalculator Calculate both Room VPD and Leaf VPD automatically Just enter the value below to generate the VPD values for your room and your plants. You’ll need to know the room’s temperature, relative humidity, and the plant’s temperature. We recommend calibrating your...

www.dimluxlighting.com

VPD charts with differentials are at the bottom of the page.

Thanks Trump.
I also forgot to say that chart is approximate
If you google them and look they are all slightly different.
So don’t get too upset if your not dead on what they have there.
Especially at first.
You can get frustrated trying to be exact.


Stay safe
Bill284

 

[Trump]

The IR meters suck pretty hard and are not in any way accurate and may be 5 degrees of from actual leaf temperature. You need a real FLIR camera to accurately measure leaf temp.

IR meters are for cooking and things that doesn't require pin point accuracy.

Yes. I understand that they aren't actual dedicated leaf temp meters but for a dedicated meter you're going to pay a pretty penny. This will at least get you somewhat close.

None of the gear most of us growers use is all that accurate but it's close enough to get us in range. Unless I'm buying lab quality gear that has been calibrated, the gear that is commercially available to us has an error range.

 

[Wastei]

Yes. I understand that they aren't actual dedicated leaf temp meters but for a dedicated meter you're going to pay a pretty penny. This will at least get you somewhat close.

None of the gear most of us growers use is all that accurate but it's close enough to get us in range. Unless I'm buying lab quality gear that has been calibrated, the gear that is commercially available to us has an error range.

You don't need a meter to follow VPD charts if you want to do that. We did fine before all the VPD charts and I to this day never use them. Before we had recommendations and they follow the new VPD charts to a tee.

It's a good tool for newcomers to grasp how to successfully lower humidity while still letting the plant grow and transpire. You will get an incorrect readings using IR thermometers on leaves. Maybe you could calibrate toward a real camera but from my experience they are note accurate and reliable.