UC and humidity

All4freedumb · Jun 5, 2012

What up Farmers.. I was wanting to get some solid info on ideal humidity for plants playing in water culture.. It's the only thing I never really kept good control of and I'm going to be changing that. My humidity in my rooms sit between 45-55. I was hoping to get some solid info on humidity levels throughout all stages. I know some of you have been very helpful in some threads with this issue, I was hoping to find it in an easy spot.. Thanks for your time guys and gals... A4FD

deacon1503 · Jun 5, 2012

I keep it 60 - 65% til week 5 then the dehuey runs 24/7 to get it as low as possible. However u must have a dehuey large enough to drain the air sufficiently when you go from lights on 65% to lights off 90% as quickly as u can or it will be playing catch up all night with girls that big breathin hard all night and sittin in buckets of water.

Ive never noticed UC specific humidity abnormalities.

All4freedumb · Jun 5, 2012

Thanks, I have never noticed and abnormalities either. I have also had great success this far in the UC. It has just made me wonder if things are this good without control, what will I see with control of humidity.. I get what your saying about a big enough dehumidifier.. I got the humidifiers now I'm looking into some good dehumidifiers. 14k each room bare bulb vert, any suggestions?

RollinEndough · Jun 5, 2012

http://urbangardenmagazine.com/2010/07/plantworks-part-1-humidity-and-vapor-pressure-deficit/

deacon1503 · Jun 6, 2012

I watch my VPD too; nice post.

Given ur plants are 14k worth of light big, ur way beyond the 65 pint range. The ideal air 100pint or a smaller sante fe maybe. Im running a few of the ideal 100's and they do well although im about to pull the trigger on a dri eaz evolution for my personal room.

Buy as much dehuey as u can afford.

ttystikk · Jun 6, 2012

Another point to consider is WHY humidity matters; it directly affects how much water- and therefore nutrients- a plant can take up. Lower humidity can lead to nute burn because the plant is transpiring too much water, this also certainly stresses them too. One response to low humidity is to close the stomata under the leaves. This leads to an inability to take up CO2, rendering CO2 augmentation effectively useless. So don't go too low.

High humidity comes with its own pitfalls; here, the plant is taking up less water, and if RH is too high, it will be unable to bring up adequate supplies. You'll see this especially in 'non-mobile' nutrients like calcium. For higher RH, you want higher EC so the plant has access to enough nutes.

Clearly, a balance is called for, and that's where the above VPD chart comes in. For veg, I recommend about 75-78 degrees and 70% RH. For early flower, go up to 80 degrees and 75% while you're pushing CO2, and then dial back the RH by 5 points a week after week 4. Remember also to lower your nutes strength at the same time, to avoid nute burn issues.

woodsmaneh · Jun 6, 2012

You need to keep you humidity quit high to get the most out of your plants.

Short answer is

Plant leaves have stomata on them, they open and close depending on humidity levels. Low humidity they are closed, high humidity they are open. The Stomata are the motor that drives plant growth so you want them open as much as possible. I keep my RH around 65 to 80% when in flower, anything less and your plants are not at optimum growth potential. If you just got to mess with them than drop the humidity to 50% for last 10 days. I do not do this. You can check out my results on this site.

Humidity and Vapour Pressure Deficit (VPD)
For years Relative Humidity (RH) has been used as a measure of how much water vapour is present in the air and is probably still the preferred method used by experienced growers. In a greenhouse, the amount of water vapour present has a direct effect on a plants ability to transpire and hence grow.
Another measure called vapour pressure deficit (VPD) is also used to indicate humidity and is felt to be more directly related to a plants wellbeing. VPD combines the effects of both humidity AND temperature into one value and so gives a good indication of plant wellbeing without the need for the grower to do any mental arithmetic. VPD values run in the opposite way to RH values so when RH is high VPD is low.
If humidity is too low (i.e. high VPD), the stomata on the leaves tend to close in order to limit transpiration and prevent wilting. This closing of the stomata will also limit the rate of CO2 uptake and hence limit photosynthesis and consequently plant growth. Low humidity also reduces turgidity (water pressure within the plant cells) and this in turn also restricts growth.
Conversely, if humidity is too high (i.e. low VPD) the stomata will fully open but even so the plants will be unable to evaporate enough water to carry minerals into the plant and so again, growth will be impeded and mineral deficiencies (particularly calcium) may occur. In addition, the plants may exhibit soft growth, fungal problems and mineral deficiency symptoms.
It is frequently stated that VPD more closely matches what the plant "feels" in relation to temperature and humidity and therefore forms a better basis for environment control. Unfortunately, VPD is extremely difficult to determine accurately as it is necessary to know the leaf tissue temperature. Attempts to measure leaf temperature reliably on an ongoing basis have often ended in disaster. One of the problems is that the plants leaves are in differing amounts of sun with some leaves in full sun, some in partial sun and others in full shade. This makes the concept of "leaf tissue temperature" particularly complex.
By measuring the temperature and relative humidity within the crop canopy the calculated VPD is still a useful measure as it combines both temperature and humidity into a single measure in a way that approximates the well-being of the crop. As an example, for many crops it is suggested that RH should be kept between the following limits at the stated temperatures:-

Temperature oC

Min RH (apply fogging)

Ideal RH

Max RH (for disease prevention)

15

-

50

73

20

46

64

80

25

60

73

86

30

70

80

89

You can see from the table that the higher the temperature is the more humidity is required by the plants. The above makes it difficult to specify control parameters as different RH settings are required at different temperatures.
Now look how much simpler this is made by using VPD as the whole of the above table is contained in just three VPD values as follows

can't get the charts to load right.

AutoVent 2 and 3 environment controllers estimate the VPD based on the air temperature and humidity in the crop canopy. It will only be close to the true figure for a healthy transpiring crop. The VPD calculator below allows the VPD to be estimated based on both air and leaf temperatures. This clearly shows the possible error in VPD due to just a 1 deg C difference between air and leaf temperature.
As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 KPa
Fogging or other humidification is usually applied at VPDs above 1.25KPa and heating and dehumidification at VPDs below 0.45KPa
Use the on-line calculator below to calculate the VPD from Air Temperature and Relative Humidity (with and without leaf temperature). You need to be connected to the internet to use this link.
VPD CALCULATOR
http://www.autogrow.com/vpd_calc.php

UCMENOW · Jun 6, 2012

VPD theory doesn't take into account essential oil production in plants. So, though it may be true plants can produce more leaf growth and overall biomass with high humidity, essential oil production typically suffers as a result.

For most plants that produce essential oils, they are produced as a means of slowing transpiration and quelling pest pressures in arid regions. This is why some of the most productive food growing regions of the planet are irrigated deserts.

Rainforests produce plants and trees with huge leaves.

Irrigated deserts produce food, fiber and medicinal herbs.

If anything, high humidity in veg with progressively lower % until bottoming out at the end bloom. Below 40% after 4 weeks in to bloom in my opinion or you're just asking for botrytis or other bud rots IMO.

ttystikk · Jun 6, 2012

All4freedumb- ask for knowlege, and it will freakin' rain textbooks around here! I find it interesting that Woodsman's preference for keeping RH high throughout the flowering phase still gets him good results, even while others drop their RH drastically through flower. I wouldn't bet against his results, I've seen the pics.

In general, higher RH in veg, then steadily decreasing RH through flower is the consensus. I prefer dropping RH slowly to allow the plants to adapt to it. I personally think making any large, sudden changes in their environment is a stress and so avoiding such big swings is generally better.

All4freedumb · Jun 7, 2012

RollinEndough said:
Another point to consider is WHY humidity matters; it directly affects how much water- and therefore nutrients- a plant can take up. Lower humidity can lead to nute burn because the plant is transpiring too much water, this also certainly stresses them too. One response to low humidity is to close the stomata under the leaves. This leads to an inability to take up CO2, rendering CO2 augmentation effectively useless. So don't go too low.

High humidity comes with its own pitfalls; here, the plant is taking up less water, and if RH is too high, it will be unable to bring up adequate supplies. You'll see this especially in 'non-mobile' nutrients like calcium. For higher RH, you want higher EC so the plant has access to enough nutes.

Clearly, a balance is called for, and that's where the above VPD chart comes in. For veg, I recommend about 75-78 degrees and 70% RH. For early flower, go up to 80 degrees and 75% while you're pushing CO2, and then dial back the RH by 5 points a week after week 4. Remember also to lower your nutes strength at the same time, to avoid nute burn issues.

woodsmaneh said:
You need to keep you humidity quit high to get the most out of your plants.

Short answer is

UCMENOW said:

VPD theory doesn't take into account essential oil production in plants. So, though it may be true plants can produce more leaf growth and overall biomass with high humidity, essential oil production typically suffers as a result.

For most plants that produce essential oils, they are produced as a means of slowing transpiration and quelling pest pressures in arid regions. This is why some of the most productive food growing regions of the planet are irrigated deserts.

Rainforests produce plants and trees with huge leaves.

Irrigated deserts produce food, fiber and medicinal herbs.

If anything, high humidity in veg with progressively lower % until bottoming out at the end bloom. Below 40% after 4 weeks in to bloom in my opinion or you're just asking for botrytis or other bud rots IMO.

Click to expand...

ttystikk said:

All4freedumb- ask for knowlege, and it will freakin' rain textbooks around here! I find it interesting that Woodsman's preference for keeping RH high throughout the flowering phase still gets him good results, even while others drop their RH drastically through flower. I wouldn't bet against his results, I've seen the pics.

In general, higher RH in veg, then steadily decreasing RH through flower is the consensus. I prefer dropping RH slowly to allow the plants to adapt to it. I personally think making any large, sudden changes in their environment is a stress and so avoiding such big swings is generally better.

Click to expand...

ttystikk said:

Another point to consider is WHY humidity matters; it directly affects how much water- and therefore nutrients- a plant can take up. Lower humidity can lead to nute burn because the plant is transpiring too much water, this also certainly stresses them too. One response to low humidity is to close the stomata under the leaves. This leads to an inability to take up CO2, rendering CO2 augmentation effectively useless. So don't go too low.

High humidity comes with its own pitfalls; here, the plant is taking up less water, and if RH is too high, it will be unable to bring up adequate supplies. You'll see this especially in 'non-mobile' nutrients like calcium. For higher RH, you want higher EC so the plant has access to enough nutes.

Clearly, a balance is called for, and that's where the above VPD chart comes in. For veg, I recommend about 75-78 degrees and 70% RH. For early flower, go up to 80 degrees and 75% while you're pushing CO2, and then dial back the RH by 5 points a week after week 4. Remember also to lower your nutes strength at the same time, to avoid nute burn issues.

Click to expand...

Now this is ALL just what I needed.. those charts are exactly what I was looking for. I want you all to know how much I appreciate all of your guys shared knowledge.
I realize I have been completely out of proper ranges by either scales or opinions. I have sat between 40-50% in Veg. With that increase needed, I'm assuming swamp coolers would be my best choice? I'm also going to look into a twin set of big dawg dehumidifiers, one for each room, so I can keep everything where it should be.. Question, what about night time humidity? Whats the optimum goal for nights?
Ttstykk, you wrote about lowering my nute strength as well as my humidity. Was that from week 4 on to start tapering my nute strength with those 5 humidity points? I'm used to a slight increase in my nutes until week 6 normally, thats why I'm asking..

Deacon, thanks man, knowing your running the 100 pints now and wanting to step it up tells me to do the sane.. 160pint big dawg in each room.?

Woods,, your the one that has been slapping this chart and knowledge down on this humidity for some time now, I was hoping you'd post this.. I've see your pics too, AMAZING.. that's all I can say.. Thanks for sharing and I definitely need to look into running humidity all the way throughout, maybe a side by side? I got an extra epi and chiller... Just need a top off..

UCMENOW, Thanks for coming thru on this.. Your insight on this is where my mind has always settled.. I've always had a hard time with high humidity levels, although I always wanted them in my veg and have. Once I started running my UCs I dropped control of my humidity while vegging and still saw better growth using the UC without touching humidity control then post UC and high humidity... Now I been thinking, what if I brought that steam back but to my UC. I'll say this, just in two days of a 15% increase only hitting 55% at high I am seeing a huge step up in the girls overall health.. Co2 goes back in tomorrow.. I can't wait to see then.. I like the tapering down. What do you do with your co2 levels while hitting with higher humidity?
Thanks again guys.... A4FD...

ttystikk · Jun 7, 2012

Props to all here- it's great when we can bring so much relevant goodness to the discussion.

To answer the question you asked me, I would tailor the humidity to the nutrient strength schedule you're most comfortable with. If you like to feed heavily through week 6, then keeping the humidity up throughout that time will likely give you the best results- and will allow the plants to take full advantage of CO2 augmentation throughout. Continuing a heavy feed as humidity drops is an invitation to tip burn, so don't do that. Therefore, in your shoes I would lower nute EC in step with lower humidity values, whenever you decide to do it.

woodsmaneh · Jun 7, 2012

This is at week 71/2 at 72% RH no CO2 two more weeks to go. :) My plants did not always look this way. I'll post more when they get closer to finish.

Yes high RH can cause issues if your not set up right, got to keep that air moving everywhere, I have lost 3 buds to bud rot in the last 12 years and they were resting against the Black and white in the corner.

If we were talking land race based genetics I would agree low RH would make the plant preform better, more natural climatic conditions. However what we grow has been so crossed and convoluted, that argument goes out the window. IMHO NL#5 which is part of just about everything out there if you go back far enough loves humidity, one reason it is so mold resistant.

But growing is a journey and we learn by trying and we know there are lots of stuff to try to mess with. Great discussion folks.

deacon1503 · Jun 7, 2012

It's not just about pints per day but also the overall efficiency of the unit. Some units are rated the same pint wise, while one uses 5 amps and the other 10. Does it have auto restart? A continuous drain? Some even have ductable intakes and exhausts. A dehuey isn't something I feel can be oversized especially when the intention is to grow trees. I remember Krusty saying he ran crazy high RH till late in the bloom stage. Also have lots and lots of air circulation. Dropping RH as low as possible has the same effect as dropping the water level in the UC late in flower.

Night time RH as low as possible.

UClover · Jun 7, 2012

Got this chart from CCH2O a few years ago, one of the most helpful things I have ever come across..

RollinEndough · Jun 7, 2012

UClover said:
Got this chart from CCH2O a few years ago, one of the most helpful things I have ever come across..

Why this isn't included in every UC purchase, I don't know, but glad to have it now nonetheless. Good one.

All4freedumb · Jun 7, 2012

deacon1503 said:
It's not just about pints per day but also the overall efficiency of the unit. Some units are rated the same pint wise, while one uses 5 amps and the other 10. Does it have auto restart? A continuous drain? Some even have ductable intakes and exhausts. A dehuey isn't something I feel can be oversized especially when the intention is to grow trees. I remember Krusty saying he ran crazy high RH till late in the bloom stage. Also have lots and lots of air circulation. Dropping RH as low as possible has the same effect as dropping the water level in the UC late in flower.

Night time RH as low as possible.

Yea, its a 10 amp, auto start. It also has ducting I believe. Ideal makes one like the one I'm speaking of.. That's what I thought about nites, thanks for answering. I will make sure my dehumidifier is the best I can find.. thanks.. Now I gotta get humidity higher, foggers didn't get it where I'd like, so its either another fogger in each room or switch to a swamp cooler in each..

All4freedumb · Jun 7, 2012

UClover said:
Got this chart from CCH2O a few years ago, one of the most helpful things I have ever come across..

Yeah man what the hell.. thanks for sharing...

deacon1503 · Jun 7, 2012

All4freedumb said:
Yea, its a 10 amp, auto start. It also has ducting I believe. Ideal makes one like the one I'm speaking of.. That's what I thought about nites, thanks for answering. I will make sure my dehumidifier is the best I can find.. thanks.. Now I gotta get humidity higher, foggers didn't get it where I'd like, so its either another fogger in each room or switch to a swamp cooler in each..

It took me 2 Ideal hueys in each room to achieve proper VPD's.

woodsmaneh · Jun 8, 2012

deacon1503 said:
It's not just about pints per day but also the overall efficiency of the unit. Some units are rated the same pint wise, while one uses 5 amps and the other 10. Does it have auto restart? A continuous drain? Some even have ductable intakes and exhausts. A dehuey isn't something I feel can be oversized especially when the intention is to grow trees. I remember Krusty saying he ran crazy high RH till late in the bloom stage. Also have lots and lots of air circulation. Dropping RH as low as possible has the same effect as dropping the water level in the UC late in flower.

Night time RH as low as possible.

That's half the battle right there ^^^and good point, my RH goes down at night to about 40/50% this also helps combat bud rot and moving air at night is very important, I have seven 16" fans in a 12 x 15 x 9h room.

I have two 15 gal auto feed humidifiers in my room and they run when lights come on only.

All4freedumb · Jun 8, 2012

deacon1503 said:
It took me 2 Ideal hueys in each room to achieve proper VPD's.

If you could do it again, what would you do? The same?

woodsmaneh said:
That's half the battle right there ^^^and good point, my RH goes down at night to about 40/50% this also helps combat bud rot and moving air at night is very important, I have seven 16" fans in a 12 x 15 x 9h room.

I have two 15 gal auto feed humidifiers in my room and they run when lights come on only.

Nice, thanks Woods.. I have two floor fans, one 16' up high (half vaulted ceiling), and 4 16' wall fans. My rooms are 13 by 12... How does that sound to you? What are you running for dehumidifying?

Thanks again guys, this thread has helped me in many ways and I feel like its only begun. To me that's like a puppy with two Peters... Knowledge is the best addiction as well as the best gift...

UC and humidity

UC and humidity

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UC and humidity

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