Vpd Survey

[1diesel1]

I would run multiple 315’s spaced out about 2.5-3’ personally. I am considering 3 in a 4x8.

But my open verticle reflector with the phillips bulb was easily as hot if not hotter to cool than my glass enclosed air cooled 600’s.

So open 630’s are out in my low ceiling small rooms amd tents. In the summer anyway but dont change my stuff often as i share house hbac with my grows and run a perpetual with no down time.

I’m digging the 315w cmh I’m using as supplemental light for my gavita 1000w.

 

[MIMedGrower]

I’m digging the 315w cmh I’m using as supplemental light for my gavita 1000w.View attachment 849438

I have been checking out your room. Looks awesome!

 

[Glow]

I’m digging the 315w cmh I’m using as supplemental light for my gavita 1000w.View attachment 849438

Cool...

 

[Monster762]

Generally you find the research is accurate. Generally if someone is finding something anecdotally it is because something else is going on that are altering outcomes - its really that simple. I've been a grower for many many years while also studying plant physiology and starting my work career with a hort apprenticeship and almost without exception the research tends to prove very accurate. I've also been dealing with a broad cross section of growers for many many years and hear all sorts of weird and wonderful things:) Put it this way if you are getting optimum growth rates at 40% humidity you must be growing some sort of genetic freak of a cannabis plant because just about all experienced growers would tell you 40% RH is way too low based on hands on experience (and not research). Again you are talking complex biochemistry and in fact optimum nutrient partitioning occurs more efficiently at higher RH than lower RH in the case of many of the nutrient ions although others such as Ca and K will be better under low RH. I do see your logic but your logic doesn't match the data - that said, this doesn't make what you are saying as necessarily incorrect. It's more a case of what else is going on? Anyway, one thing I always say to people is each to their own. Its your crop and your yields so how you go about things is entirely up to you.

Hers my theory. 40 n under the whole grow. Uptake is still ridiculous. 2 times a day still full strength. Demanding more. So in my case I have found low rh very usable with this strain. Way outside of vpd. I’m no pro no warehouse grower but my chit is consistently fire n vpd aint playing too much a part in it.

 

[3 balls]

Hers my theory. 40 n under the whole grow. Uptake is still ridiculous. 2 times a day still full strength. Demanding more. So in my case I have found low rh very usable with this strain. Way outside of vpd. I’m no pro no warehouse grower but my chit is consistently fire n vpd aint playing too much a part in it.View attachment 850876View attachment 850877View attachment 850878View attachment 850879

Looking good bro. When I started this thread I was wondering if I might be missing the boat by having my dehues permanently set at 45. I have my environment "in range" now and the only noticeable result has been nightmares about bud rot.:) Still way too early to draw any conclusion though. I have read a ton more about it and even though I wouldn't put it on the top of the list of things to worry about in a grow, here is what I expect I will see.
Veg- growth wont slow to a crawl in the dry indoor winter months.
Genetics- I may have better luck growing strains that gave me hell before.
Summer- I think the very hottest days might not hurt me as much.

But we will see, I cant rule out I will just end up with PM and bud rot.

 

[MIMedGrower]

I dont know if i mentioned this before but in ed rosenthals old book he tested every paramerer extensively that growers are still arguing today.

He found temperature is very important to results but different humidity didnt change the quality of the flowers. Our plant thrives in a wide range of humidity.

 

[Monster762]

Looking good bro. When I started this thread I was wondering if I might be missing the boat by having my dehues permanently set at 45. I have my environment "in range" now and the only noticeable result has been nightmares about bud rot.:) Still way too early to draw any conclusion though. I have read a ton more about it and even though I wouldn't put it on the top of the list of things to worry about in a grow, here is what I expect I will see.
Veg- growth wont slow to a crawl in the dry indoor winter months.
Genetics- I may have better luck growing strains that gave me hell before.
Summer- I think the very hottest days might not hurt me as much.

But we will see, I cant rule out I will just end up with PM and bud rot.

Idk I’ve run both in range and out. Usually in. And it’s good but this time rh has been uncontrollably low. So I just met water demands. Then started seeing fading. My little experience tells me an even fade but otherwise healthy plant. Bump feeds. So I bumped they looked better. Bumped more n they started taking more water up.
Yesterday I had power outage 20 degrees f n all fans n all cut 3 hrs in to lights on. So last night it hit like 80% and 59 degrees. Not good but it all is clean no molds nothing. Little Lysol in the air in the room not in tent just to feel better.

 

[PharmHand]

Hers my theory. 40 n under the whole grow. Uptake is still ridiculous. 2 times a day still full strength. Demanding more. So in my case I have found low rh very usable with this strain. Way outside of vpd. I’m no pro no warehouse grower but my chit is consistently fire n vpd aint playing too much a part in it.View attachment 850876View attachment 850877View attachment 850878View attachment 850879

Your humidity is likely higher than you think it is. If your sensor is near a light or has light shining into it you will get a false reading (lower).
Multiple sensors, multiple brands and or high quality units placed throughout room and an average taken is the only way to get a DECENT idea of what the plants are actually feeling. Most rh sensors are junk and readings between different units will be all over the map even the same units placed side by side will give different readings.
The air surrounding a healthy leaf is at 100% rh as it transpires, it needs air movement to create the deficit required for transpiration. So fans and air circulation also change what the plant is actually feeling. A small room or tent with a full canopy will give you even less accurate of an idea what your plants are feeling since the air above the canopy will be low but as you go down thru the layers of leaves the humidity will rise sharply. So maybe the tops of the plants are in low rh but on average the plant as a whole isn’t experiencing what you think it is. Not to say your plants won’t grow/develop to your satisfaction since everyone has different goals/expectations , it’s just something to consider and manipulate accordingly.
Another thing to remember is water/nutrient uptake isn’t a good indication of how a plants performing since nutrients are NOT food/energy for the plant they are essentially the glue that binds the major plant constituents carbon/hydrogen/oxygen - which make up 90% of plant tissue- together. The energy comes from the light, the carbon and oxygen the air and hydrogen from water in the air and medium. The carbon can only be assimilated by means of entry thru the stomata which is why vpd is so important since the deficit determines how open those stomata are- less open as rh declines. So basically it’s a super fuckin complicated series of chemical reactions determined largely by environmental conditions. So your best course of action is to dial in your room as close to scientifically proven ideals as possible to reap the maximum amount of hi quality bud. There’s a lot of info out there for open minds that will improve your garden or you could spend decades doing your own trial and error likely never truly understanding what it is you’re trying to accomplish. :)

 

[Monster762]

Your humidity is likely higher than you think it is. If your sensor is near a light or has light shining into it you will get a false reading (lower).
Multiple sensors, multiple brands and or high quality units placed throughout room and an average taken is the only way to get a DECENT idea of what the plants are actually feeling. Most rh sensors are junk and readings between different units will be all over the map even the same units placed side by side will give different readings.
The air surrounding a healthy leaf is at 100% rh as it transpires, it needs air movement to create the deficit required for transpiration. So fans and air circulation also change what the plant is actually feeling. A small room or tent with a full canopy will give you even less accurate of an idea what your plants are feeling since the air above the canopy will be low but as you go down thru the layers of leaves the humidity will rise sharply. So maybe the tops of the plants are in low rh but on average the plant as a whole isn’t experiencing what you think it is. Not to say your plants won’t grow/develop to your satisfaction since everyone has different goals/expectations , it’s just something to consider and manipulate accordingly.
Another thing to remember is water/nutrient uptake isn’t a good indication of how a plants performing since nutrients are NOT food/energy for the plant they are essentially the glue that binds the major plant constituents carbon/hydrogen/oxygen - which make up 90% of plant tissue- together. The energy comes from the light, the carbon and oxygen the air and hydrogen from water in the air and medium. The carbon can only be assimilated by means of entry thru the stomata which is why vpd is so important since the deficit determines how open those stomata are- less open as rh declines. So basically it’s a super fuckin complicated series of chemical reactions determined largely by environmental conditions. So your best course of action is to dial in your room as close to scientifically proven ideals as possible to reap the maximum amount of hi quality bud. There’s a lot of info out there for open minds that will improve your garden or you could spend decades doing your own trial and error likely never truly understanding what it is you’re trying to accomplish. :)

True you’ve got a couple points there. I keep hygrometer strapped there cause I can put it right at canopy level n read it from door. I have 16 inch fans 1 at canopy rotating and 1 underneath blowing upwards on rotate across the bottom of the canopy
whole house humidity is in 30s.
Furnace heat.

 

[PharmHand]

True you’ve got a couple points there. I keep hygrometer strapped there cause I can put it right at canopy level n read it from door. I have 16 inch fans 1 at canopy rotating and 1 underneath blowing upwards on rotate across the bottom of the canopy
whole house humidity is in 30s.
Furnace heat.

If you had one tiny plant in the center of your tent and an accurate hygrometer you’d have a good number for what the plant is truly experiencing. The tighter the canopy the more the plants will feel the humidity they’re generating

 

[3 balls]

I'm curious if anyone else has any findings to report as a result of vpd tinkering since I started this thread a few crops back?

A few things I "think" I learned.


If scrogging or similar air flow needs to be insanely adequate.

In the last couple or few weeks when the growing is done I think the benefits of it are gone and higher RH just becomes a threatening factor.

Building materials are a sponge- wood, concrete etc. So when you want to dial it down towards the end don't expect it to happen overnight. On that same note, if you have multiple spaces/rooms with different stages of life cycle it can get tricky.

 

[Phylex]

I don't have the gear and space to remain in the VPD curve. But I bounce in and out of it and remain fairly close most of the time. Until I have a sealed room and equipment that can hold RH and temps this will have to do. But I've been happy with the results so far.

 

[Dirtbag]

I stay pretty much in the green curve, around 73-75F and 60-70% RH through veg, and 50-60 RH most of flower till the last 2 weeks I drop it to 40-50 RH.

If my humidity is lower uncontrollably I just put less nutes in the water and water more often. Not a huge deal but you do need to compensate.

 

[Mr.Juice]

Just to throw in my two cents, newbie grower, but I do know a thing or two about science.

Couple points that I think should be brought to attention:

The VPD chart is assuming a 2 degree temp difference between leaf temperature and env temp. If you want to religiously test the results versus ideal VPD values, you would have to take leaf temperatures and do the calculations.
In addition, each plant has hundreds of leaves, all at differing points within the canopy so there is no “single” VPD value for any particular plant. It is an aggregate of values.

My personal take away, the chart is a guide. An extra tool to estimate conditions. Does VPD have an effect on a plant, absolutely. Can you have a successful harvest without adhering to the VPD chart, absolutely.

 

[3 balls]

My personal take away, the chart is a guide. An extra tool to estimate conditions. Does VPD have an effect on a plant, absolutely. Can you have a successful harvest without adhering to the VPD chart, absolutely.

I absolutely agree. It's not something that has to be precise or even close to it. If I was able to talk to my 5 years ago self I would summarize it simply; worry about 10 other things first, if you cant keep your veg at least 45% put a humidifier on your wish list, and lastly, you don't need to keep your dehumidifier on full blast in flower.

 

[Hdinkleman]

im growing two plants in 20% humidity
it hasnt gotten over 40% in my tent
cloning next to my kitchen sink temps range from 50-70F

screw vpd doesnt make a difference for me