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Thanks for the link, but I'd like to keep this thread focused on VPD theory applied to drying & curing.
Mold grows in h2o saturated air (low VPD), and you get that by ignoring VPD.Mold grows best over 75f and you lose terps. Not good idea to use vpd for drying.
Good place to be. At 80f and 64%- not a good place.I’m drying in my tent right now. I have a ac infinity 6” cloudline running on a 67 controller. It’s the newer controller with Bluetooth etc. it gives a vpd readout. I have leaf temp offset set to zero and fan is running on 3 at minimum and 8 on high. The same controller is also running my t4 supply fan. My settings are maintaining 60% rh and temp is currently 68 degrees. The controller is giving a vpd reading of .99 kpa
My temps and rh are constant and the buds are currently 4 days from chop. I checked them for the first time today and they are drying nice and slow. No hay smell in the tent.
Thank you for the first hand testimony.I’m drying in my tent right now. I have a ac infinity 6” cloudline running on a 67 controller. It’s the newer controller with Bluetooth etc. it gives a vpd readout. I have leaf temp offset set to zero and fan is running on 3 at minimum and 8 on high. The same controller is also running my t4 supply fan. My settings are maintaining 60% rh and temp is currently 68 degrees. The controller is giving a vpd reading of .99 kpa
My temps and rh are constant and the buds are currently 4 days from chop. I checked them for the first time today and they are drying nice and slow. No hay smell in the tent.
Yes I know, I’m not using vpd to dry. I just offered what the vpd is in my tent while drying at my set temp and rh.Good place to be. At 80f and 64%- not a good place.
Min temp 67.2Thank you for the first hand testimony.
That controller can give the VPD average over a span of time, could you post the max/min/average for those days? No need to export to a file, it's just 3 numbers.
Yep, that's the gist of it...VPD is essentially the same reasoning during dry and cure as it is for growing… its used to control the rate of the movement of water through the plant tissue
During dry and curing we use it to slow the water movement thatGreenhouse Condensation Control: Understanding and Using Vapor Pressure Deficit (VPD) allows certain processes to continue that would stop if moisture gets to low.
First 3 days are usually lower humidity higher temps to lower the moisture on the exterior of the bud to prevent mold, bacterial or fungal infection. Then we go higher RH and lower temp to prevent the outside from getting to dry and allow the moisture to evenly be drawn out of the bud.
This slow even draw of moisture is very key to allow the breakdown and conversion of chlorophyll, starches etc. through chemical and biological reactions and processes. If it dries to fast it stops
Thats the basic idea and youll find varying opinions on thia subject.
[...]several studies that explore disease pathogen survival at different climate levels reveal two critical values of VPD. Studies show that fungal pathogens survive best below 0.062 psi VPD (<0.43 kPa). Furthermore, disease infection is most damaging below 0.030 psi (0.20 kPa). Thus, the greenhouse climate should be kept above 0.062 psi (>0.43 kPa), to prevent disease and damage to crops.
This is because you want water movement always exiting the tissue never entering as it then becomes a vector for infection. I have long said that rehydration of your buds is not a good idea for this reasonYep, that's the gist of it...
Here is a very clear scientific paper (a fact sheet, in fact) on using VPD for both fungual and disease control by controling condensation in greenhouses I just dug up for us...
It goes deeper into VPD's effect on when condensation & evaporation will occure, and give insight on management at any temprature.
And here are the important details:
However, that is *very saturated* air, and I'm thinking a VPD range of 1.0-1.1 is going to be near ideal for drying, and well out of range of disease/mold levels.
Also when reaching dew point in the grow its is ideal for infection. Also long said ppl dont pay enough attention to the humidity just after lights out. I say this because the lights go off and the temperature drops fast and RH being RELATIVE humidity (relative to temperature) that means the humidity spikes up fast and can reach dew point quickly that most never even onow this is happening until its to late. When this happens a few days in a row bam infection.Yep, that's the gist of it...
Here is a very clear scientific paper (a fact sheet, in fact) on using VPD for both fungual and disease control by controling condensation in greenhouses I just dug up for us...
It goes deeper into VPD's effect on when condensation & evaporation will occure, and give insight on management at any temprature.
And here are the important details:
However, that is *very saturated* air, and I'm thinking a VPD range of 1.0-1.1 is going to be near ideal for drying, and well out of range of disease/mold levels.
Dry days & humid nights is the end of an Arizona Summer... and I am juggling temp/RH with 2 different evaporative cooler systems and 2 micro climates (an uninsulated well ventilated enclosed 10'x20'x15' shop, and a 4x4x7 AC Inf. tent in that shop).Also when reaching dew point in the grow its is ideal for infection. Also long said ppl dont pay enough attention to the humidity just after lights out. I say this because the lights go off and the temperature drops fast and RH being RELATIVE humidity (relative to temperature) that means the humidity spikes up fast and can reach dew point quickly that most never even onow this is happening until its to late. When this happens a few days in a row bam infection.
The worst grow condition is dray days and humid nights. This is ideal for spore germination and spore dispersion
Humid days and dry nights are fine butbi wont get into that
I've got the same ac controller and fan and will be using it to dry for the first time soon. I'm hella nervous. So much work to screw it up at the end. I almost want to take a week off work so I can monitor it. But I'm going to count on that controller to maintain 60%. My temps should run around 68°.I’m drying in my tent right now. I have a ac infinity 6” cloudline running on a 67 controller. It’s the newer controller with Bluetooth etc. it gives a vpd readout. I have leaf temp offset set to zero and fan is running on 3 at minimum and 8 on high. The same controller is also running my t4 supply fan. My settings are maintaining 60% rh and temp is currently 68 degrees. The controller is giving a vpd reading of .99 kpa
My temps and rh are constant and the buds are currently 4 days from chop. I checked them for the first time today and they are drying nice and slow. No hay smell in the tent.
I found 70f at 50% for 3 days then 60-63 at 60% until ready to jar. Depending on bud size anywhere from 10-20 days. Just what i found to work well for me.I've got the same ac controller and fan and will be using it to dry for the first time soon. I'm hella nervous. So much work to screw it up at the end. I almost want to take a week off work so I can monitor it. But I'm going to count on that controller to maintain 60%. My temps should run around 68°.
70f @ 50% is ~1.45 kPa, and 60-63 @ 60% is ~0.8-0.9 kPaI found 70f at 50% for 3 days then 60-63 at 60% until ready to jar. Depending on bud size anywhere from 10-20 days. Just what i found to work well for me.
Sensor placement is key. Air movement is key but never directly at the buds
Many ways to skin a drying an curing cat… just need to keep the principal in mind and you will do fine brother. No hard rules just goals to strive for and what works for me70f @ 50% is ~1.45 kPa, and 60-63 @ 60% is ~0.8-0.9 kPa
I'd have to use at least 2 different temp/RH combos... one starting a bit after dawn, and the other, after sunset... to sustain that VPD...
Evaporative coolers have a hard limit: they max out at a 40f temp drop from outdoor ambient @ <10% humidity. Also, as humidity rises, this max temp drop goes down.
So I can't drop and hold a ~110f+ outdoor ambient temp to more than about 82-84f in the tent... but I can drive up humidity to bring it to those VPD targets by using a dual micro-climate approach and running the 2nd evap cooler in the shop's ambient (around 100f+ and 30% RH) and venting the tent's humidity back into the shop.
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