Vpd (vapor Pressure Deficit) What It Means To My Plants

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DemonTrich

DemonTrich

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Forgot to mention, I only follow VDP guidelines in veg only. In flower, I run sealed, deheuy, ac and co2. My rh is 65% weeks 1 thru 4, then 60 for 2 wks, 55 for 2 weeks, then 50% until harvest. Flower room ambient temps are 82*, leaf temps taken on 12 plants are 78 amd 79 all around.
 
Funkadelic

Funkadelic

808
93
Im curious how to best manage, regularly and without nasty toxins, the PM... at these high humidities... omfg the PM...

I believe VPD to be the most important aspect of growth I've missed paying close attention to.
 
jumpincactus

jumpincactus

Premium Member
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See this is my problem as well. I'm not as concerned with PM, its just in my environment I would be chasing my tail attempting a near perfect VPD as the Rh around here is very low, (10%) think desert. So even with a ultrasonic fogger for added humidity because my ventilation runs full tilt to keep 2000w hps heat gain down I would be drawing the moisture out as soon as the fogger puts it in the room. For the same reason I also quit running C02. Fans run all during lights on and running C02 is a waste, right out the vent pipe....... Whats a man to do??? I just dont have the funds to spend like some of the heavy hitters. Sounds like grow room envy LOL
 
Seamaiden

Seamaiden

Living dead girl
23,597
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Im curious how to best manage, regularly and without nasty toxins, the PM... at these high humidities... omfg the PM...

I believe VPD to be the most important aspect of growth I've missed paying close attention to.
Physical blockers if high pH water isn't doing the trick. All you need to do here is kill the fruiting bodies. JMS Stylets oil, peroxide(s), I've even used isopropyl alcohol to kill fruiting bodies.
 
A_j_207

A_j_207

167
93
Good morning Farmers. Just when I thought I knew just about everything about controlling our ladies environments,I stumbled upon this. So what is VPD and what does it mean to my cannabis? Read on.

As mentioned, I am new to this particular term and the associated science data connected to it so if anyone has any personal insight on if you personally use this data in managing your climates what observations have you made and more importantly how you go about getting the sweet spot indicated on the attached graphs. There is also other data out there with claims that less than ideal VPD levels will actually mimic nutrient deficiencies.

I would add that I am in no way advocating this as a must have to grow great cannabis, but I would like to know if anyone who believes in this has seen any measurable results good or bad. Initially my position was "oh great, just one more thing to stress over and control in my gurls world. However is this is solid science and has it been proven to keep our gals happier and healthier than by all means let me have it. Call me a skeptic but I do fare from Mizzourah. I look forward to those in the "know and who actually monitor and use this data for their grows.......... Enjoy.......



Vapor Pressure Deficit - The Hidden Force on your Plants
Once you understand what vapor pressure deficit is, all those environmental factors you're trying to juggle in your mind suddenly click into place and you start to think and feel like a plant. Take a few minutes to understand why VPD management is key to creating the perfect indoor growing environment! Your plants will thank you for it!
Humidity is HUGE when it comes to growing plants. An important milestone in becoming a competent and responsive grower is developing an understanding of what humidity is, how plants respond to it, and how you can manage and manipulate it

Firstly, let's make sure we're all on the same page. When we speak of the "humidity" of or in the air we are basically referring to the amount of water in the air. "In the air?" What do we mean? Well, water can only truly stay in the air when it is in gas form - aka "water vapor". We're not talking about tiny droplets of water in the air here (e.g. fog or mist.)



tomato_plant_suffering_from_high_temperatures_and_arid_conditions_low_humidity.jpg

Unsurprisingly, temperature plays a crucial role when it comes to humidity. The warmer the air, the more water vapor it can potentially hold. As the amount of water air can hold constantly changes with temperature it can be difficult to get a handle on what we need to measure. Fortunately an answer comes in the form of the concept of "Relative Humidity" (RH) - this is a measurement in terms of percentage, of the water vapor in the air compared to the total water vapor potential that the air could hold at a given temperature.


So, when we say there's a relative humidity of 50% - we mean "At this specific temperature, the air is carrying half the potential water vapor possible."

The Effect of Relative Humidity on Your Plants
RH can be easily measured using digital or analogue meters called "hygrometers." They are available for around $15 at your local indoor gardening store. But what do the readings mean for your plants?

Turns out-they mean a great deal! While many novice growers focus solely on keeping temperature in range, many take their eye off the ball as far as RH is concerned-perhaps because they don't fully understand what it is or how to manipulate it to their advantage.

Have you ever been to Florida in July? You'll know that it's not just the heat that's oppressive, it's the humidity! You feel constantly wet with sweat - the whole place feels like a sauna you can't escape from! (Sorry Floridians!)

RH has an ever more direct effect on plants. Plants need to "sweat" too - or rather, they need to transpire (release water vapor through their stomata) in order to grow.

The amount of water plants lose through transpiration is regulated, to a point, by opening and closing their stomata. However, as a general rule, the drier the air, the more plants will transpire.


Under Pressure
All gasses in the air exert a certain "pressure." The more water vapor in the air the greater the vapor pressure. What does this mean? Well, in high RH conditions (think of Florida again) there is a greater vapor pressure being exerted on plants than in low RH conditions. From a plant's perspective, high vapor pressure can be thought of as an unseen force in the air pushing on the plants from all directions. This pressure is exerted onto the leaves by the high concentration of water vapor in the air making it harder for the plant to 'push back' by losing water into the air by transpiration. This is why with high RH plants transpire less. Conversely, in environments with low RH, only a small amount of pressure is exerted on the plants' leaves, making it easy for them to lose water into the air.

What is Vapor Pressure Deficit (VPD)?
Okay, so now that you have RH firmly implanted into your conceptual map, we move on to Vapor Pressure Deficit or VPD. As implied by the word "deficit" we're talking about the difference between two things. In this case, it's the difference between the theoretical pressure exerted by water vapor held in saturated air (100% RH at a given temperature) and the pressure exerted by the water vapor that is actually held in the air being measured at the same given temperature.




vapor_pressure_deficit_explained.gif



The VPD is currently regarded of how plants really 'feel' and react to the humidity in the growing environment. From a plant's perspective the VPD is the difference between the vapor pressure inside the leaf compared to the vapor pressure of the air. If we look at it with an RH hat on; the water in the leaf and the water and air mixture leaving the stomata is (more often than not) completely saturated -100% RH. If the air outside the leaf is less than 100% RH there is potential for water vapor to enter the air because gasses and liquids like to move from areas of high concentration (in this example the leaf) into areas of lower concentration (the air). So, in terms of growing plants, the VPD can be thought of as the shortage of vapor pressure in the air compared to within the leaf itself.

Another way of thinking about VPD is the atmospheric demand for water or the 'drying power' of the air. VPD is usually measured in pressure units, most commonly millibars or kilopascals, and is essentially a combination of temperature and relative humidity in a single value. VPD values run in the opposite way to RH vales, so when RH is high VPD is low. The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant.
As mentioned above, VPD provides a more accurate picture of how plants feel their environment in relation to temperature and humidity which gives us growers a better platform for environmental control. The only problem with VPD is it's difficult to determine accurately because you need to know the leaf temperature. This is quite a complex issue as leaf temperature can vary from leaf to leaf depending on many factors such as if a leaf is in direct light, partial shade or full shade. The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy. For humidity control purposes it's not necessary to measure the actual leaf VPD to within strict guidelines, what we want is to gain insight into is how the current temperature and humidity surrounding the crop is affecting the plants. A well positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions.

Managing Humidity
Managing the humidity in your indoor garden is essential to keep plants happy and transpiring at a healthy rate. Transpiration is very important for healthy plant growth because the evaporation of water vapor from the leaf into the air actively cools the leaf tissue. The temperature of a healthy transpiring leaf can be up to 2-6°C lower than a non-transpiring leaf, this may seem like a big temperature difference but to put it into perspective around 90% of a healthy plant's water uptake is transpired while only around 10% is used for growth. This shows just how important it is to try and control your plants environment to encourage healthy transpiration and therefore healthy growth.
So what should you aim to keep your humidity at? Many growers say a RH of 70% is good for vegetative growth and 50% is good for generative (fruiting /flowering) growth. This advice can be followed with some degree of success but it's not the whole story as it fails to take into account the air temperature.



humidifier_increases_relative_humidity.jpg


Photo credit: Aquaculture Hydroponics, UK.




vapor_pressure_deficit_relative_humidity_chart_small.jpg

By looking at this example we can see that at 70% RH the temperate should be between 72-79°F (22-26°C) to maintain healthy VPDs. If your growing environment runs on the warm side during summer, like many indoor growers, a RH of 75% should be maintained for temperatures between 79-84°F (26-29°C.)


The problem with running a high relative humidity when growing indoors it that fungal diseases can become an issue and carbon filters become less effective. It is commonly stated that above 60% RH the absorption efficiency drops and above 85% most carbon filters will stop working altogether. For this reason it is good practice to run your RH between 60-70% with the upper temperature limit depending on your crop's ideal VPD range, in the example it would be 64-79°F (18-26°C.)

The table also shows that if your temperature is above 72°F (22°C), 50% RH becomes critically low and should generally be avoided to minimize plant stress.
Please understand that by presenting this information we do not want you to go to your indoor gardens and run your growing environment to within strict VPD values. What's important to take from this is that VPD can help you provide a better indication of how much moisture the air wants to pull from your plants than RH can.
If you want to work out for yourself the VPD of your plants leaves you can follow the steps below:

Measure the leaf temperature and look up the vapor pressure at 100% RH on the table below.



vapor_pressure_deficit_relative_humidity_chart_small2.jpg

Measure the air temperature and relative humidity and look up the nearest vapor pressure figure on the above table.


Subtract the air vapor pressure from the leaf vapor pressure:

Example:
Leaf Temperature = 24°C (100% RH) Leaf VP: 29.8
Air Temperature = 25°C @ 60% RH Air VP: 19.0
VPD= 10.8

Humidity's Effect on Plants
Plants cope with changing humidity by adjusting the stomata on the leaves. Stomata open wider as VPD decreases (high RH) and they begin to close as VPD increases (low RH). Stomata begin to close in response to low RH to prevent excessive water loss and eventually wilting but this closure also affects the rate of photosynthesis because CO2 is absorbed through the stomata openings. Consistently low RH will often cause very slow growth or even stunting. Humidity therefore indirectly affects the rate of photosynthesis so at higher humidity levels the stomata are open allowing co2 to be absorbed.



thai_basil_leaf_curl_localized_low_humidity_stress.jpg



When humidity gets too low plants will really struggle to grow. In response to high VPD plants will try to stop the excessive water loss from their leaves by trying to avoid light hitting the surface of the leaf. They do this by rolling the leaf inwards from the margins to form tube like structures in an attempt to expose less of the leaf surface to the light, as shown in the photo.

For most plants, growth tends to be improved at high RH but excessive humidity can also encourage some unfavorable growth attributes. Low VPD causes low transpiration which limits the transport of minerals, particularly calcium as it moves in the transpiration stream of the plant - the xylem. If VPD is very low (95-100% RH) and the plants are unable to transpire any water into the air, pressure within the plant starts to build up. When this is coupled with a wet root zone, which creates high root pressure, it combines to create excessive pressure within the plant which can lead to water being forced out of leaves at their edges in a process called guttation. Some plants have modified stomata at their leaf edges called hydathodes which are specially adapted to allow guttation to occur. Guttation can be spotted when the edges of leaves have small water droplets on, most evident in early morning or just after the lights have come on. If you see leaves that appear burnt at the edges or have white crystalline circular deposits at the edges it could be evidence that guttation has occurred.



tomato_plants_exhibiting_guttation_excessive_humidity_levels.jpg



Most growers are well aware that with high humidity comes and increased risk of fungal diseases. Water droplets can form on leaves when water vapor condenses out of the air as temperature drops, providing the perfect breeding ground for diseases like botrytis and powdery mildew. If humidity remains high it further promotes the growth of fungal diseases. The water droplet exuded through guttation also creates the perfect environment for fungal spores to germinate inviting disease to take hold.



powdery_mildew_takes_hold_after_poor_humidity_control.jpg



Low VPD / High RH High VPD / Low RH

Mineral deficiencies Wilting
Guttation Leaf roll
Disease Stunted plants
Soft growth Leathery/crispy leaves
What a great read. Thank you very much
 
ziplock

ziplock

90
33
Im curious how to best manage, regularly and without nasty toxins, the PM... at these high humidities... omfg the PM...

I believe VPD to be the most important aspect of growth I've missed paying close attention to.
Me, too. I've taken to using a pan of water under a small circulation fan. It bumps the rH around 10%, which brings mine into the 45-50% range. Maybe not ideal, but a whole lot better. (I have a small grow space; about 24 sf)
 
RudyClosGrow

RudyClosGrow

23
3
Good morning Farmers. Just when I thought I knew just about everything about controlling our ladies environments,I stumbled upon this. So what is VPD and what does it mean to my cannabis? Read on.

As mentioned, I am new to this particular term and the associated science data connected to it so if anyone has any personal insight on if you personally use this data in managing your climates what observations have you made and more importantly how you go about getting the sweet spot indicated on the attached graphs. There is also other data out there with claims that less than ideal VPD levels will actually mimic nutrient deficiencies.

I would add that I am in no way advocating this as a must have to grow great cannabis, but I would like to know if anyone who believes in this has seen any measurable results good or bad. Initially my position was "oh great, just one more thing to stress over and control in my gurls world. However is this is solid science and has it been proven to keep our gals happier and healthier than by all means let me have it. Call me a skeptic but I do fare from Mizzourah. I look forward to those in the "know and who actually monitor and use this data for their grows.......... Enjoy.......



Vapor Pressure Deficit - The Hidden Force on your Plants
Once you understand what vapor pressure deficit is, all those environmental factors you're trying to juggle in your mind suddenly click into place and you start to think and feel like a plant. Take a few minutes to understand why VPD management is key to creating the perfect indoor growing environment! Your plants will thank you for it!
Humidity is HUGE when it comes to growing plants. An important milestone in becoming a competent and responsive grower is developing an understanding of what humidity is, how plants respond to it, and how you can manage and manipulate it

Firstly, let's make sure we're all on the same page. When we speak of the "humidity" of or in the air we are basically referring to the amount of water in the air. "In the air?" What do we mean? Well, water can only truly stay in the air when it is in gas form - aka "water vapor". We're not talking about tiny droplets of water in the air here (e.g. fog or mist.)



tomato_plant_suffering_from_high_temperatures_and_arid_conditions_low_humidity.jpg

Unsurprisingly, temperature plays a crucial role when it comes to humidity. The warmer the air, the more water vapor it can potentially hold. As the amount of water air can hold constantly changes with temperature it can be difficult to get a handle on what we need to measure. Fortunately an answer comes in the form of the concept of "Relative Humidity" (RH) - this is a measurement in terms of percentage, of the water vapor in the air compared to the total water vapor potential that the air could hold at a given temperature.


So, when we say there's a relative humidity of 50% - we mean "At this specific temperature, the air is carrying half the potential water vapor possible."

The Effect of Relative Humidity on Your Plants
RH can be easily measured using digital or analogue meters called "hygrometers." They are available for around $15 at your local indoor gardening store. But what do the readings mean for your plants?

Turns out-they mean a great deal! While many novice growers focus solely on keeping temperature in range, many take their eye off the ball as far as RH is concerned-perhaps because they don't fully understand what it is or how to manipulate it to their advantage.

Have you ever been to Florida in July? You'll know that it's not just the heat that's oppressive, it's the humidity! You feel constantly wet with sweat - the whole place feels like a sauna you can't escape from! (Sorry Floridians!)

RH has an ever more direct effect on plants. Plants need to "sweat" too - or rather, they need to transpire (release water vapor through their stomata) in order to grow.

The amount of water plants lose through transpiration is regulated, to a point, by opening and closing their stomata. However, as a general rule, the drier the air, the more plants will transpire.


Under Pressure
All gasses in the air exert a certain "pressure." The more water vapor in the air the greater the vapor pressure. What does this mean? Well, in high RH conditions (think of Florida again) there is a greater vapor pressure being exerted on plants than in low RH conditions. From a plant's perspective, high vapor pressure can be thought of as an unseen force in the air pushing on the plants from all directions. This pressure is exerted onto the leaves by the high concentration of water vapor in the air making it harder for the plant to 'push back' by losing water into the air by transpiration. This is why with high RH plants transpire less. Conversely, in environments with low RH, only a small amount of pressure is exerted on the plants' leaves, making it easy for them to lose water into the air.

What is Vapor Pressure Deficit (VPD)?
Okay, so now that you have RH firmly implanted into your conceptual map, we move on to Vapor Pressure Deficit or VPD. As implied by the word "deficit" we're talking about the difference between two things. In this case, it's the difference between the theoretical pressure exerted by water vapor held in saturated air (100% RH at a given temperature) and the pressure exerted by the water vapor that is actually held in the air being measured at the same given temperature.




vapor_pressure_deficit_explained.gif



The VPD is currently regarded of how plants really 'feel' and react to the humidity in the growing environment. From a plant's perspective the VPD is the difference between the vapor pressure inside the leaf compared to the vapor pressure of the air. If we look at it with an RH hat on; the water in the leaf and the water and air mixture leaving the stomata is (more often than not) completely saturated -100% RH. If the air outside the leaf is less than 100% RH there is potential for water vapor to enter the air because gasses and liquids like to move from areas of high concentration (in this example the leaf) into areas of lower concentration (the air). So, in terms of growing plants, the VPD can be thought of as the shortage of vapor pressure in the air compared to within the leaf itself.

Another way of thinking about VPD is the atmospheric demand for water or the 'drying power' of the air. VPD is usually measured in pressure units, most commonly millibars or kilopascals, and is essentially a combination of temperature and relative humidity in a single value. VPD values run in the opposite way to RH vales, so when RH is high VPD is low. The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant.
As mentioned above, VPD provides a more accurate picture of how plants feel their environment in relation to temperature and humidity which gives us growers a better platform for environmental control. The only problem with VPD is it's difficult to determine accurately because you need to know the leaf temperature. This is quite a complex issue as leaf temperature can vary from leaf to leaf depending on many factors such as if a leaf is in direct light, partial shade or full shade. The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy. For humidity control purposes it's not necessary to measure the actual leaf VPD to within strict guidelines, what we want is to gain insight into is how the current temperature and humidity surrounding the crop is affecting the plants. A well positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions.

Managing Humidity
Managing the humidity in your indoor garden is essential to keep plants happy and transpiring at a healthy rate. Transpiration is very important for healthy plant growth because the evaporation of water vapor from the leaf into the air actively cools the leaf tissue. The temperature of a healthy transpiring leaf can be up to 2-6°C lower than a non-transpiring leaf, this may seem like a big temperature difference but to put it into perspective around 90% of a healthy plant's water uptake is transpired while only around 10% is used for growth. This shows just how important it is to try and control your plants environment to encourage healthy transpiration and therefore healthy growth.
So what should you aim to keep your humidity at? Many growers say a RH of 70% is good for vegetative growth and 50% is good for generative (fruiting /flowering) growth. This advice can be followed with some degree of success but it's not the whole story as it fails to take into account the air temperature.



humidifier_increases_relative_humidity.jpg


Photo credit: Aquaculture Hydroponics, UK.




vapor_pressure_deficit_relative_humidity_chart_small.jpg

By looking at this example we can see that at 70% RH the temperate should be between 72-79°F (22-26°C) to maintain healthy VPDs. If your growing environment runs on the warm side during summer, like many indoor growers, a RH of 75% should be maintained for temperatures between 79-84°F (26-29°C.)


The problem with running a high relative humidity when growing indoors it that fungal diseases can become an issue and carbon filters become less effective. It is commonly stated that above 60% RH the absorption efficiency drops and above 85% most carbon filters will stop working altogether. For this reason it is good practice to run your RH between 60-70% with the upper temperature limit depending on your crop's ideal VPD range, in the example it would be 64-79°F (18-26°C.)

The table also shows that if your temperature is above 72°F (22°C), 50% RH becomes critically low and should generally be avoided to minimize plant stress.
Please understand that by presenting this information we do not want you to go to your indoor gardens and run your growing environment to within strict VPD values. What's important to take from this is that VPD can help you provide a better indication of how much moisture the air wants to pull from your plants than RH can.
If you want to work out for yourself the VPD of your plants leaves you can follow the steps below:

Measure the leaf temperature and look up the vapor pressure at 100% RH on the table below.



vapor_pressure_deficit_relative_humidity_chart_small2.jpg

Measure the air temperature and relative humidity and look up the nearest vapor pressure figure on the above table.


Subtract the air vapor pressure from the leaf vapor pressure:

Example:
Leaf Temperature = 24°C (100% RH) Leaf VP: 29.8
Air Temperature = 25°C @ 60% RH Air VP: 19.0
VPD= 10.8

Humidity's Effect on Plants
Plants cope with changing humidity by adjusting the stomata on the leaves. Stomata open wider as VPD decreases (high RH) and they begin to close as VPD increases (low RH). Stomata begin to close in response to low RH to prevent excessive water loss and eventually wilting but this closure also affects the rate of photosynthesis because CO2 is absorbed through the stomata openings. Consistently low RH will often cause very slow growth or even stunting. Humidity therefore indirectly affects the rate of photosynthesis so at higher humidity levels the stomata are open allowing co2 to be absorbed.



thai_basil_leaf_curl_localized_low_humidity_stress.jpg



When humidity gets too low plants will really struggle to grow. In response to high VPD plants will try to stop the excessive water loss from their leaves by trying to avoid light hitting the surface of the leaf. They do this by rolling the leaf inwards from the margins to form tube like structures in an attempt to expose less of the leaf surface to the light, as shown in the photo.

For most plants, growth tends to be improved at high RH but excessive humidity can also encourage some unfavorable growth attributes. Low VPD causes low transpiration which limits the transport of minerals, particularly calcium as it moves in the transpiration stream of the plant - the xylem. If VPD is very low (95-100% RH) and the plants are unable to transpire any water into the air, pressure within the plant starts to build up. When this is coupled with a wet root zone, which creates high root pressure, it combines to create excessive pressure within the plant which can lead to water being forced out of leaves at their edges in a process called guttation. Some plants have modified stomata at their leaf edges called hydathodes which are specially adapted to allow guttation to occur. Guttation can be spotted when the edges of leaves have small water droplets on, most evident in early morning or just after the lights have come on. If you see leaves that appear burnt at the edges or have white crystalline circular deposits at the edges it could be evidence that guttation has occurred.



tomato_plants_exhibiting_guttation_excessive_humidity_levels.jpg



Most growers are well aware that with high humidity comes and increased risk of fungal diseases. Water droplets can form on leaves when water vapor condenses out of the air as temperature drops, providing the perfect breeding ground for diseases like botrytis and powdery mildew. If humidity remains high it further promotes the growth of fungal diseases. The water droplet exuded through guttation also creates the perfect environment for fungal spores to germinate inviting disease to take hold.



powdery_mildew_takes_hold_after_poor_humidity_control.jpg



Low VPD / High RH High VPD / Low RH

Mineral deficiencies Wilting
Guttation Leaf roll
Disease Stunted plants
Soft growth Leathery/crispy leaves
Very good info for understanding these common occurrences in plant development. It's the reason why I sometimes need to water more with low RH and water much less when the humidity is high.
 
jumpincactus

jumpincactus

Premium Member
Supporter
11,612
438
Very good info for understanding these common occurrences in plant development. It's the reason why I sometimes need to water more with low RH and water much less when the humidity is high.
you will also find that if you use about an inch of mulch on top you will find you have to water less often. I use par boiled rice hulls for a mulch layer. Works great.
 
P

Pimples

772
143
I dont need to read this to tell you to rock 70-85% humidity with 80 degree temps and co2 1000-1100 ppm. Ive seen the growth before my own.eyes. we run sealed with equipment to extract or add humidity so its ALWAYS perfect. That temp and humidity is used until end of.week 4 then down to 50-60% humidity and 75 degree temps. That is the secret recipe thanks @JACKMAYOFFER
This is the real secret to bumper yields. I take it even further and in the last 3 weeks or even 2 I drop temps and rh even lower. But in veg and early flower..high temps high rh and blast with gas really pushes them. Any base nutrient will do. And if thats the case..stop giving hydroponic marketed bottles your wallet and go with Jacks 3 2 1 . If your able to control the climate like this..manage the canopy for multiple bud site nodes and have the correct anount and quality of light..all you need is a high yielding cultivar . Nutrients are last on the list if at all. 5This is how you pull 2 plus pounds off of 100 watt hid's. Or 20 to 25 ounces off sixers. Or you COB nerds that pull insane numbers for the amount of juice you use. Its not really a secret. Just expensive to have the right equipment to control perfect climate and never dependent on what its like outside. I truly believe that 70% of so called nutrient problems are really problems with climate. Once i went sealed room with the right equipment..I never saw so called calcium or magnesium or potassium or whatever false reads from plants ever again.
 
P

Pimples

772
143
I'm a new believer in the power of VPD. I've been fighting tipburn even though ppms are at the low range in my Blumat reservoirs (going into gallon smartpots with bagged coco).

My new baby comes tomorrow, an ESSICK AIR Space Saver 821 000 evaporative humidifier:
View attachment 486235
WhooHoo, coming up from the new Amazon distribution center in Dupont, free Prime for 30 days!

I'm near Seattle so I didn't expect to need humidity but my (outside air exchange) flower room averages 78F and 40%rh during lights on. Lights are up to 2800W of LED wall power. I bought a decent dehumidifier but I've never plugged it in during the 14 months I've run this room.

. . . or maybe I just need more calcium, from MGRox's Ratio thread (from another source):
By contrast, several costly Ca‐deficiency disorders occur in horticulture. . . These generally arise when sufficient Ca is momentarily unavailable to developing tissues. Deficiency symptoms are observed (a) in young expanding leaves, such as in ‘tipburn’ of leafy vegetables.
Hueys in veg room for sure. High humidity..high temps. Blast co2. With t5..and cmh lamps. Wow. Super fast veg. Insane root growth.
 
P

Pimples

772
143
See this is my problem as well. I'm not as concerned with PM, its just in my environment I would be chasing my tail attempting a near perfect VPD as the Rh around here is very low, (10%) think desert. So even with a ultrasonic fogger for added humidity because my ventilation runs full tilt to keep 2000w hps heat gain down I would be drawing the moisture out as soon as the fogger puts it in the room. For the same reason I also quit running C02. Fans run all during lights on and running C02 is a waste, right out the vent pipe....... Whats a man to do??? I just dont have the funds to spend like some of the heavy hitters. Sounds like grow room envy LOL
In my opinion..if you cant afford the cost of a mini split and commercial grade dehuey..i wouldnt even bother with sealed room and co2. Just vent traditionally and get what you get..which isnt a bad thing at all. Iam in Michigan. Temps weather and humidity is all over the place 365 days a year. I was always a slave to whatever my intakem.ducted lights and gave me. I mean really. Cold as intake for air cooled hoods and room intake in February sucks. As does 85 degrees and 70%rh in July/August. Just a loss pf control really. But i pulled it off..for years. Sealing up the rooms and with the right equipment gives me total control. But its pricey. Really pricey.
 
P

Pimples

772
143
Im curious how to best manage, regularly and without nasty toxins, the PM... at these high humidities... omfg the PM...

I believe VPD to be the most important aspect of growth I've missed paying close attention to.
In mu experience its not high humidity that always gave me powdery mildew (if it wasnt hidden in a gifted cut). It was the radically different fluctuating rh and temps that gave me the spots. Having it warm and humid...cold and humid...warm amd dry....cold and dry..no consistency whatsoever..that's ground zero for the dreaded p.m.
 

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