Optimizing VPD for drying?

M

Mothperson

Member
Given that everyone's drying conditions are different and many people have the ability to control at least one of temp or humidity, can VPD be used to optimize drying conditions or as a general guide that makes sense regardless of local environment? I imagine the same principles would apply as in the growing process. Has anyone done this or is there a general VPD range for drying? I know there are charts for growing, but I would assume that drying would be different since the only goal is to remove water at a specific rate.
 
Mothperson said:
Given that everyone's drying conditions are different and many people have the ability to control at least one of temp or humidity, can VPD be used to optimize drying conditions or as a general guide that makes sense regardless of local environment? I imagine the same principles would apply as in the growing process. Has anyone done this or is there a general VPD range for drying? I know there are charts for growing, but I would assume that drying would be different since the only goal is to remove water at a specific rate.
Click to expand...
Atoms. Out with the old in with the new.
 
Dontjudgeme said:
Not to my knowledge. Drying is relatively simple in comparison to growing.
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It does feel like that. My humidity and temp have been way more stable than main tent. My temps (75F) are slightly higher than people recommend (63-68 , but my RH (50-55) has been floating on the top end of what I’ve seen suggested (40-55), so I wondered if the higher temp (faster dry) is balanced by the higher RH (slower dry).
 
VPD is a moot point since you are at harvest not growing. All you have to do is dry in as stable of an environment as you do , low and slow. Drying can take easily 10 days plus. Everyone has their “ preferred “ zone , but I shoot for 60-70° temp and about 60 to 65 Rh.
That way most of the work has been done and then I can step down the Rh to match desired storage Rh.
62% is common , but like 58% better In jar.

RH too low , buds dry out too quickly.
RH too high , mold.

Recommend Hygrometers to monitor dry space .
 
LinguaPeel said:
Put a jar with a hygrometer in the fridge, the RH goes up. Does that mean cold causes mold? Or makes the weed moister?
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This question kind of adds to what I'm curious about.. as in maybe drying a.k.a "curing" can be optimized by running on the higher end of the RH range, but at colder temps to avoid mold all together (though I don't know enough about mold to support this).
 
I don't have the personal supply to take major risks right now, but I can't wait until I do. I want to do some fucked up things to my cannabis to see what happens.
 
Dontjudgeme said:
Not to my knowledge. Drying is relatively simple in comparison to growing.
Click to expand...

I think its quite the opposite. Drying/harvest is the number one way that people fuck up their grow. Everyday there are new threads about how someone dried their plants for 2 days and put them in a jar and it smells like lawn clippings.
 
Cannabis can be stored in refrigerator under some conditions , checking it every so often . Heard actually for years , however I indulge
far too much to carry stock that long. My seeds however are stored in fridge container with a desiccant pack.

The decapitated heads in my freezer get frost burn from time to time tho.
 
So going by a vpd chart you can have your temp at 59° and as long as you RH is 45%-55% all is well and plant will love it? So if I move heaven and earth to match temp to vpd sweet spot humidity I'm good?
 
I think the whole scheme can be changed. In tobacco they use precise conditions to cause the leaves to turn brown, this makes them smoke smoother. Why don’t we do this with chronic. That’s what I want to aim for.
 
I read some of that, looks like it has to do with high temps for a short amount of the, which I don’t want. I want the plant to turn brown just like the leaves on the trees, or leaves that fall off trees. But also conserve the terppz.

Might as well mention it now. I have heard people say ‘bacteria break down the chlorophyll’. Bacteria! People!? So where are the bacteria, inside the cells of the plant? Outside? Or do people mean Enzymes. ?
 
SnidleyBluntash said:
I read some of that, looks like it has to do with high temps for a short amount of the, which I don’t want. I want the plant to turn brown just like the leaves on the trees, or leaves that fall off trees. But also conserve the terppz.

Might as well mention it now. I have heard people say ‘bacteria break down the chlorophyll’. Bacteria! People!? So where are the bacteria, inside the cells of the plant? Outside? Or do people mean Enzymes. ?
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"As current research activities have focused on symbiotic or parasitic plant–microbe interactions, other types of associations between plants and microorganisms are often overlooked. Endophytic bacteria colonize inner host tissues, sometimes in high numbers, without damaging the host or eliciting strong defense responses. " - https://www.sciencedirect.com/science/article/abs/pii/S1369526611000549
 
Mothperson said:
Given that everyone's drying conditions are different and many people have the ability to control at least one of temp or humidity, can VPD be used to optimize drying conditions or as a general guide that makes sense regardless of local environment? I imagine the same principles would apply as in the growing process. Has anyone done this or is there a general VPD range for drying? I know there are charts for growing, but I would assume that drying would be different since the only goal is to remove water at a specific rate.
Click to expand...

I too am pondering VPD. I'm just about to cut and start drying. The "60/60" rule I've come to believe is common, suggests a very specific VPD (0.72), and it's a rather humid one. For those who don't know Air VPD, it's effectively the pressure (or lack of) the moisture in the air exerts on the plant. There is also "Leave VPD" which is effectively the pressure the plant holds against the air, or very much the compliment of Air VPD. A VPD of 1.0 is balanced. A VPD of 0.0 would essentially be immersion in water and a VPD above 1 means the air will start taking up the moisture the plant respires.

SO, a VPD of 0.72 is humid (as if 60/60 didn't describe that well enough). If we are trying to dry the plant, we want the Air VPD to be higher than the leaf VPD (the plant gives off the moisture because the air has less vapor pressure than the plant.

As I understand it, "Drying" is really about slowly removing enough moisture that we don't have to worry about mold and such, and in that process there are chemical changes as well (Chlorophyll leaving with the water I think).

All that said, 60/60 is a cool, but humid environment. Isn't that what many molds like, or am I mistaken and they (the ones we'll encounter anyway) prefer warmer, hence the 60f?
 
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