Vapor Pressure Deficit & What It Means To You!

[bobrown14]

I like my humidity between 50-60% and temps 70-80F

Comfy for me and the plants. Sadly its a rare occasion here in Philly but its a thing now. YAY

 

[NorthernCosmos]

Nooo! Too much information - as in something new to worry about

Joking aside, that's a great article, and even without a leaf/ambient temp difference measurement, I can say that I've probably been growing exclusively in the lower right danger zone with an assumed VPD greater than 2.0. Temps are at 26-22 C and RH at no more than 40% - I've been struggling to keep it that cool and humid...

Having read this thread, I'll be working towards getting into the green zone

 

[Stormblessed]

Yes awesome info and I love learning it, I just need to work on keeping a consistent environment b4 I can try to fine tune it that precisely

 

[Archiweedies]

Nooo! Too much information - as in something new to worry about

Joking aside, that's a great article, and even without a leaf/ambient temp difference measurement, I can say that I've probably been growing exclusively in the lower right danger zone with an assumed VDP greater than 2.0. Temps are at 26-29 and RH at no more than 40% - I've been struggling to keep it that cool and humid...

Having read this thread, I'll be working towards getting into the green zone

What I’ve found works for me the best, is to first control the temps (canopy temps checked with a laser temp gun) as accurately as I can. I shoot for a day/night difference of about 8-10 degrees Fahrenheit. I use a controller to do that. Then, once you have that dialed in, you can use a combination of humidifiers and dehumidifiers to suit the humidity for the stage of your plants development.
I should mention that if you run your humidity at 60% plus during veg you could cause your charcoal filter to wear out faster.

Yes awesome info and I love learning it, I just need to work on keeping a consistent environment b4 I can try to fine tune it that precisely

Hopefully some of the advice I gave NorthernCosmos above helps you out as well


I’m glad you guys enjoyed the article, thanks for taking the time to comment.

 

[Stormblessed]

Thank u for taking the time to do the research work for us

 

[Gazoo]

SIDE NOTE: There are two types of LASER temp meters, Make sure its not the kind that reads
body temp, they read different by about 4 degrees to compensate.

Also most have a 3.5 F error margin, not great when your looking for 3.0 deg F difference,
good idea to VERIFY using cup of ICE & Water

 

[NorthernCosmos]

I should mention that if you run your humidity at 60% plus during veg you could cause your charcoal filter to wear out faster.

I can confirm that as I got a clogged filter from a runaway atomizing humidifier. The combination of 70-something % RH spike and quite a bit of calcium in the water (fine white powder everywhere) clogged up my filter. I saved the filter though, the story is here:

What airflow to expect from extractor filter & fan combo?

I have a 2x4 tent with an 100mm extractor system consisting of a Blauberg Turbo-E 100 rated at 187m3/hr (110cfm) and a Hy-Filter rated at 250 m3/hr (147cfm). The filter has the supplied pre-filter jacket around it. Less than 1m of alu flex tubing is used with two slight bends. This should be a...

www.420magazine.com

Right now the RH is on the rise here, having crept up to ~ 65% ambient (50-something in the tent), and my temps are at 32C. This should actually give a better VPD than previously.

I've only been growing since September last year, so I still have to learn about how the changing seasons affects the conditions in the tent and devise methods to control it. There are a couple of no-budget things I can do right now: vent the exhaust outside to not build up so much hot air in the room and move the LED power supplies outside the tent. An IR thermometer gun is on the list of equipment to get - I've been needing one for a while anyway!

 

[Archiweedies]

Thank u for taking the time to do the research work for us

I was glad to do it

SIDE NOTE: There are two types of LASER temp meters, Make sure its not the kind that reads
body temp, they read lower by bout 4 degress to compensate.

Also most have a 3.5 F error margin, not great when your looking for 3.0 deg F difference,
good idea to VERIFY using cup of ICE & Water

hiya Gazoo!
You’re absolutely correct and thank you for mentioning that. The cheap temp gun I use is from Harbor Fart.
I run into this a lot in my furniture making where it’s easy to get hung up on tolerances. I invested in a Starrett 12” combination square several years ago and paid about $130 brand new. These are manufactured to much more strict tolerances than the ones they sell at your local big box store. My square isn’t the absolute best on the market, there are more precision instrument but the cost shoots skyward very fast.
I suppose what I’m saying is, environmental control can be very precise if you are willing to drop the coin. For me, I found it cheaper to control humidity because my humidity controller can control downy to plus or minus 1%. Then I shoot for 27-28C with lights on.
Of course, one of these days I’ll move into the house where it’s insulated and it would most likely be easier to keep the temps pegged at a certain temp and adjust the humidity instead.
Hope that helps!

 

[Archiweedies]

I can confirm that as I got a clogged filter from a runaway atomizing humidifier. The combination of 70-something % RH spike and quite a bit of calcium in the water (fine white powder everywhere) clogged up my filter. I saved the filter though, the story is here:

What airflow to expect from extractor filter & fan combo?

I have a 2x4 tent with an 100mm extractor system consisting of a Blauberg Turbo-E 100 rated at 187m3/hr (110cfm) and a Hy-Filter rated at 250 m3/hr (147cfm). The filter has the supplied pre-filter jacket around it. Less than 1m of alu flex tubing is used with two slight bends. This should be a...

www.420magazine.com

Right now the RH is on the rise here, having crept up to ~ 65% ambient (50-something in the tent), and my temps are at 32C. This should actually give a better VPD than previously.

I've only been growing since September last year, so I still have to learn about how the changing seasons affects the conditions in the tent and devise methods to control it. There are a couple of no-budget things I can do right now: vent the exhaust outside to not build up so much hot air in the room and move the LED power supplies outside the tent. An IR thermometer gun is on the list of equipment to get - I've been needing one for a while anyway!

I also get the white powder from my water using my humidifier and I suspect that factors in here as well. Thank you for your comment!
You’re on the right path, in my mind, because you are recognizing that conditions change when the seasons change for a lot of us. Keep refining your techniques for dealing with these changes and document them. Soon enough, you’ll know exactly how to manipulate your environment right to where you want it.

 

[TorturedSoul]

I can confirm that as I got a clogged filter from a runaway atomizing humidifier. The combination of 70-something % RH spike and quite a bit of calcium in the water (fine white powder everywhere) clogged up my filter.

High humidity also slows transpiration, interfering with the plants' ability to self-cool.

 

[Gazoo]

I was glad to do it

hiya Gazoo!
You’re absolutely correct and thank you for mentioning that. The cheap temp gun I use is from Harbor Fart.
I run into this a lot in my furniture making where it’s easy to get hung up on tolerances. I invested in a Starrett 12” combination square several years ago and paid about $130 brand new. These are manufactured to much more strict tolerances than the ones they sell at your local big box store. My square isn’t the absolute best on the market, there are more precision instrument but the cost shoots skyward very fast.
I suppose what I’m saying is, environmental control can be very precise if you are willing to drop the coin. For me, I found it cheaper to control humidity because my humidity controller can control downy to plus or minus 1%. Then I shoot for 27-28C with lights on.
Of course, one of these days I’ll move into the house where it’s insulated and it would most likely be easier to keep the temps pegged at a certain temp and adjust the humidity instead.
Hope that helps!

Hiya Buddy

Yes I like cheap cost, the point being the VERIFICATION once you have a adjustment number
to apply to the readin its easy.

OH Yeh who would of thunk the RED LASER DOT is not the spot you are reading at !
or the size of the area being read, most are using 12:1 distance to reader (1 inch reading dia at 12 inches)
I had to add some rods that extent exactly 3 inches and centered on the lens
when leaf is centered the area being read is 1/4 inch dia. helps for the small seedling / early veg leafs

 

[Gazoo]

I also get the white powder from my water using my humidifier and I suspect that factors in here as well. Thank you for your comment!
You’re on the right path, in my mind, because you are recognizing that conditions change when the seasons change for a lot of us. Keep refining your techniques for dealing with these changes and document them. Soon enough, you’ll know exactly how to manipulate your environment right to where you want it.

I have a Revers Osmosis water filter system so only use that in my Humidifiers, not only is there
no white powder but humidifiers last so much longer . I am convinced the cost is cheaper
when I factor in the cost of replacement

 

[NorthernCosmos]

I changed from using an atomizing humidifier to an evaporative one after my clogged filter episode. It can't saturate the air like an atomizing or vaporizing one, but it has some other advantages:
- not being able to create humidity spikes, which can be seen as a safety feature w.r.t. filter clogging
- there's no more white powder, the calcium and other minerals/impurities end up at the bottom of the water reservoir
- it cleans the air to some degree, catching dust and particles

 

[TorturedSoul]

What's the downside, if any? More electricity use? More heat produced? Etc.

 

[NorthernCosmos]

The downside would be that it can't (over...) saturate the air like the atomizing/vaporizing ones. The power usage isn't much; usually just a fan motor. The fan blows enough that it contributes to air circulation in the tent.

The fan blows air through the "wicking" material - actually a rotating half submerged drum with lots of thin discs in mine, others use a porous combined wick and filter - and then the air will absorb moisture from being blown through that. So rather than putting (potentially too much) water molecules/droplets into the air, the air grabs only the water it "wants" to carry, so to speak.

 

[Gazoo]

What's the downside, if any? More electricity use? More heat produced? Etc.

For me the large room Humidifier downsides are the cost of Filters approx
25 a piece but if you use the anti bacterial additive they cam last a few runs.
No heat issues

Also the size is a limitation

 

[TorturedSoul]

Oh, okay. When I read "evaporative," I pictured some kind of heating element, lol. But it's more like the drum type ones that go on HVAC runs just after the furnace, then? Gotcha.

 

[bobrown14]

I read on Colorado's extension website that the difference in temps in the grow room from 22C to 24C is the higher temps produce 40% more THC. I read it... don't make it true just passing along what I read.

 

[Pennywise]

You gonna put it to the test?

 

[bobrown14]

My flower room these daze is pretty much dialed to 24C. It sometimes fluctuates when I'm in there blowing a lot of hot air! lol

My new grow space is perfect for temps and rH but my first full size grow haven't had a full harvest yet.