Humidity levels??

[Rrains007]

I have been growing for about 4 years. Those 4 years I ran a semi large grow for a group who just told me what they wanted the percentages and ppm to be, whether it be humidity or co2. Just like every topic around growing there seems to be a big debate amongst a lot of growers particularly because what they say and think is the gospel lol. I'm interested in what humidity levels in flower and veg that you guys run, particularly those of you who used to do it one way and changed because you saw improvements. I personally feel that without testing certain parameters there's no way to say what is right and what is wrong.

What I currently do is 60 percent first week flower, 55 second, 50 third, 45 fourth and 40 the rest of the way. Night time i keep it 10 percent lower, except when it hits week 4 and on and I keep it at 40 percent night and week 5 going toward I leave it at 35.

As for veg I run it at 65 day and 55 at night.

thanks to anyone who gives insight.

[YYCannabis]

VPD is what all the cool kids are into now a days. 😉 I’ve learned that there is no such thing as a “golden rule” for growing cannabis, but more of “golden ranges”. Add in the fact that no 2 growers are ever the same when they are biased towards what has worked for them personally. I guess the only way to know what your plants want is to grow generations of them and test the golden ranges to see what makes them grow best.

Sounds like you have a very well controlled environment. I wish i could get The Bank Of Mrs YYC to let me add to my climate control system 😒

[Rrains007]

Totally get the vpd aspect. I appreciate you commenting too man. I just never used vpd because it encompass temp and humidity and not co2. When it comes to the bank I totally get that lol. 21 lighter and 110k deep 😥 lol. I'll definitely take a closer look at it though. Thanks for your time!

[YYCannabis]

I’ve not looked into how CO2 affects VPD (I don’t run CO2) but VPD is about controlling how well the plant “breathes”. If taking in CO2 while breathing at their VPD best, it can only help i would think. I’m sure there’s plenty of articles on line covering it in more specific terms for CO2.
I’d be interested to know what you discover.

[gbauto]

What I've experienced over the years is that issues with pm/mold seem to be dependent on the strain I'm running.
Air movement in the grow space is vital.
This link has a bunch of info: https://pulsegrow.com/blogs/learn/vp...ect#chart-calc
I find that the girls are much happier when I'm able to run a specific vpd value.
Since I run led's in ambient air, I try to keep the room @ 83 degF which will give a leaf surface temp of 80 degF(I use an IR temp gun).
Vpd is a measure of the difference of water vapor pressure inside of the leaf and the air surrounding the leaf surface.
Here's a note from the article: Getting your VPD right will give you the best results in your grow. VPD influences five key things, that are all somewhat related.

Stomata Opening
As VPD increases, stomata get smaller.

CO2 uptake
As VPD increases and stomata get smaller, CO2 uptake gets reduced.

Transpiration
As VPD increases, the plant transpires (evaporates from leaves) faster due to the larger difference in vapor pressures between the leaf and the air.

Nutrient intake at the roots
As VPD increases and transpiration increases, the roots pull in more nutrients. The plant is like one connected system of plumbing!

Plant stress
As VPD increases, there are more forces acting on the plant – from the leaves to the roots – and the plant experiences more stress.

As you can see there’s a complicated tradeoff between VPD and a variety of factors. You can increase how much CO2 the plant absorbs, but reduce the amount of nutrition. You can increase the amount of nutrition but also stress the plant more. VPD is a very powerful tool in the grower’s toolbox. To get the best results you need to find the correct VPD sweet spot for the plant’s stage of growth.

Since CO2 allows you to run a warmer room, you just use the corresponding temp/rh combo to get you close to an ideal vpd.
The chart shown in the pulse link is what I run.
Just remember that you need to know what the leaf surface temps are to get the corresponding rh range.
If you're using the pulse graph to look up temp/rh targets, it's the leaf surface temp that you plug into the graph, not the ambient air temp.
I typically run my room at 60% rh in flower-lots of air movement

[Rrains007]

YYCannabis I do run co2. From 750 to 1500 ppm depending on stage. After your last message I checked out the vpd chart and it scares me to go that high in humidity just because of bud rot lol

[YYCannabis]

Found this from a quick google....see pic.
Bud rot and WPM can be prevented with correct airflow. What are you running for temps?

[Rrains007]

YYCannabis I'm running 78 day and 70 night. I have 20 hurricane fans running in a 28x24 room. 21 gavita 1000w lights.

[gbauto]

The important number is what the leaf temp stabilizes under the broilers.
This why HID has to run a lower room and leaf temp because of the IR radiation they emit.
If the strains you're using are susceptible to pm/bud rot that doesn't respond to increased air movement, just try to keep the temp/rh close to the ideal vpd by running a cooler room temp.
Hi leaf temps and low rh stresses the plants-think drought conditions.
The plant responds by slowing down its metabolism to survive.

[YYCannabis]

Do you have the ability to lower your temps?

[grouchyoldman]

I'll offer up this handy VPD Chart from Pulse Labs. The "Green Zone" range of Temp/RH% purportedly represents conditions conducive to our breathing plants. Like many cannabis topics the application of theory to reality is a bit ambiguous. I try to keep my room "in the Zone," at least when it coincides with common sense. Caveat Emptor.

@gbauto, you seem very authoritative on this subject, Does this chart seem accurate & complete. I notice the "Green Zone" extends into *really* extreme combinations in both the top Left and lower Right. Can that be right?

[gbauto]

Hey, old grouch.
When I run that chart using leaf surface temps, the plants are always quite happy.
I agree that some strains are more susceptible to pathogens that require really stressing the environment for the bug as well as the plants.
Just remember that as the vpd increases, so does the internal vascular pressure of the plant trying to move moisture.

[Anansi]

Alright, I'll bite. I had to Google VPD to find out what it was. I found the Pulse site. What I discovered is that there is some science geek shit going on that I can't totally get my head around. I understand the importance of keeping temp and humidity in a optimum range, but measuring the difference in ambient temperature and leaf temperature in order to fine tune the environment seems like overkill. I'm not suggesting that it doesn't work, only asking is it worth it. Does the cost/benefit ratio pay off? With the cost of equipment necessary to maintain temperature and humidity at precise levels and all the time and effort needed to implement and maintain the environment, does it result in a corresponding improvement in yield and quality?

I love growing marijuana (sounds like a good name for a seed bank). But it is just a hobby. So convince me of the merits of such an endeavor.

[YYCannabis]

Hi Anansi.
Yeah, it’s a bit of a science geek thing, but in it’s simplest form, its a way to make sure that the plant can properly moving energy and sugars from greens to roots and back to greens again.
A high VPD means your plant can start to dry out. It might look like wind burn or heat stress.
A low VPD means your plant’s growth can be stunted because nutrients and sugars are not getting moved around in the plant. This can cause nutrient deficiency.

Any way you look at it, weed will grow *better* following a VPD chart. You can still grow good stuff without worrying about it, but to help get the best out of your plants it’s something to be aware of and try to stay within the correct VPD range. So to answer your question about cost benefit...I’d say it depends on what your end goal is and how much money it will cost you to maintain a healthy VPD.

[Anansi]

It seems like this is like most other hobbies. Different people have different goals and different levels of enthusiasm. I like to target shoot. Not in competition, just for fun. I spend lots of time and some money tweaking the gun and ammo to be able to shoot a 1/2" group instead of 3/4" group. Does that make any difference in the real world? No. Is it fun to try? Yes. Growing weed is the same way. I now produce weed that rivals dispensary fare. Question is, do I want to spend the time and money to make it even better. Interesting to consider. I like this thread -- I've learned something new today. Merry Christmas.

[YYCannabis]

Yup. Different levels of enthusiasm for different growers.

[Anansi]

Another question: CO₂ and VPD control. Would it be reasonable to implement these separately? Or, in order to get the advantage of one, do you necessarily need the other?

YYCannabis I see you are concerned with VPD, but don't add CO₂. Do you mind telling me what type equipment you use to control VPD? Thanks.

[YYCannabis]

Correct. No point dumping money into a CO2 system if it’s wasted from plants not breathing it in.
As for what people use to regulate VPD, it totally depends on their environment they are in. I’m in a winter environment so my challenge is getting temp to correspond with the humidity in the tent. All I need is a small heater in my tent to help me maintain VPD targets. Other growers need full-on dehumidifiers or humidifiers, A/C or heaters.

[Anansi]

I was trying to make this way more complicated than it actually is. I was thinking it required specialty equipment such as a humidistat controlled humidifier/dehumidifier. I've already got an ac unit that has a dehumidifier mode, a small evaporative type humidifier, a thermostat-controlled electric heater, and monitoring meters. I live in the mid-south where humidity is my biggest issue -- too low in the winter, too high in the summer. Up until now, my goal was to keep the temperature in the 70ish degree range and the humidity in the 50-60 range. I check my plants daily and adjust the equipment as necessary to try to maintain that. According to the VPD chart, those figures are about right. Even the blind sow finds an acorn every now and then. If I read the instructions correctly, I want a VPD of .8 for seedlings, 1.0 for veg, and 1.2 - 1.5 for flower. I'll pay attention to the chart on my next grow to see how accurate I can keep it. Thank you for sharing.

[YYCannabis]

My system is simple for my situation. I have a small heater and an exhaust fan....that’s it. To control them I’m using Inkbird controllers from Amazon. One for Temp and one for humidity.

https://www.amazon.com/dp/B01N56KEU6/ref=cm_sw_em_r_mt_dp_hs84FbNJ06YGY

[Woodsman67]

Great thread to read. Thanks to all