Dark period before harvest

[Locrian99]

Curious what people think of the 48 hour dark period before harvest. I know some do it, it’s not necesarry has anyone for sure seen benefits from it as opposed to that’s just always how I’ve done it? I’m curious the same for drying. Obviously don’t have a bright Light right on them. But does the room need to be black, or can there be some light. Thx all.

[CaptainShamrock]

Subbed. Curious about this as well.

[Campesino]

We were discussing this on another thread, but I agree it deserves its own.
I will summarize what I have learned through fairly extensive research.
Cannabis is a C3 plant. As such it does not need any darkness during vegetation. The Calvin cycle, which is sometimes known as the "dark cycle" operates in C3 plants all the time or they are dead. It is inaccurately called the "dark cycle" because it does not need light, however it also does not need darkness.
During light, your plant produces sugars and other chemicals needed to run the Calvin cycle. Your plant stores a portion of these for use when there is no light so that the Calvin cycle can continue and the plant doesn't die.
Now the interesting part...
The production of most cannabinoids is powered by the Calvin cycle. So they are being produced 24 hours a day in the later part of flowering even though the lights are on only 12 (or less!?). Light actually degrades compounds like THC. In some parts of the plant, light degrades them faster than the plant can produce them. Thus, your plant is making THC all 24 hours, but a portion is burning off when the lights are on. You need to keep running the lights so that the plant can do all that it needs and recharge its reservoirs to power the Calvin cycle. But at harvest, you no longer care about the long term health of the plant. Leaving it in extended darkness depletes you plants reservoirs as it will continue powering the Calvin cycle (and making THC) as long as it can.
The above is also why most growers harvest in the morning or before the lights come on, even if they don't do extended darkness.
If you are growing Autos and leaving them on long days up to harvest, I would also consider this carefully.
I plan to increase darkness to 14 hours for the final weeks of Flower and will leave the plants in darkness (if I can, there are more than one) for 48 hours before harvest.

[abadtrip]

@ campesino Can u please direct me to the base of your findings because I have read scientific papers done in labs that say a dark period does nothing and light does not degrade thc. I would love to read the science u have because it contradicts everything I have been reading from the science community.

[Campesino]

@abadtrip
I'm working on it, but have to actually go to work, so I will get back to you

[Campesino]

@abadtrip
As I said, I am going to work to put together some notes and citations on this. I have been poking around during free time today, but will need some time to pull things together and be able to share sources. It feels more like work, and I actually have enough of that right now, so I'll do my best. In the mean time, I want to reiterate my confidence in the information I provided.
Something about your comment has bothered me today. You are asking to know my sources, but didn't share your own. Your comment challenged the veracity of the information I provided by making reference to "scientific papers done in labs". Your challenge obligates me to respond with my sources. I feel you should be similarly obligated to share yours.
I am an academic and "affiliated" with a university. I have access to journal articles. If all you have are citations, I will be happy to fetch the articles.

[DingusKhan]

Thanks again Campesino. When my seeds arrive, I'm doing that too. I hadn't heard that about harvest in the morning. There's another potency boost!

[greenforce]

When drying avoid direct light but, I find that temp & humidity much more crutial. The old ones always said the best place to dry herbs is in the hayloft. Too bad we all don't have one of those puppies.
Be good, G

[greenforce]

Right on D69 ! lofts, grainbend's old cellars & smoke houses. You never know what that mean stud horse in the barn might be standing on or under. Pardon me for the short version of your name. The auto correct is bumming my tablet experience in this end. G
at his end. ,...............

[D.A.A.S.69]

Hey GF, no problems with the spelling, but yeah, you damn right , that's where everything happened was in the barn, or loft, an I do mean everything, a special place.

[ZigZag]

My drying and curing has worked best when the humidity is about 50% and the temp is about 72 degrees F. Anything warmer or dryer seems to dry them too fast.
Never had any issues with mold, rot or anything like that (knock on wood). I get a dry time of 5-7 days under those conditions and then a careful cure for the next few weeks and then the jars seem to stabilize after that. No lights except occasional weak lamp light when I'm in and out of the room.

[Ell]

Have not darkene them last couple harvest. If anything, plants seem a couple of days better. If that makes sense.

[D.A.A.S.69]

I quit feeding an watering my plants 2-3 days before harvest, so the dry only takes 4-5days not a week, hang them in the dark 2-3days in a closet. Then brown paper bags ,gently shake the bags every day a couple of times, the bags have Hydrometer in them, when close to 50-60percent humidity I put them in jars with Bovedas.
My outdoor plants we cover up totally with black plastic an do them the same. No scientist, but I can promise you ,you'll see alot more trichs if you keep them in the black dark a few days before chopping.

[ALASKAGREEN]

DASS

What brand of hydrometer do you use? I need to buy some.

[D.A.A.S.69]

Hey AlaskaGreen, I know your plants have got to be very close to harvest, if you haven't already. I got a bunch of the small kind Nebula talks about on GWE, about 20bucks a piece. They work great, but the cheaper ones on Amazon work ok, you might need to calibrate them ,but that's easy to do.

[ZigZag]

Next time I harvest I'm going to try lights out for 3 days before taking them down. I'll take some macro shots of the trichomes before and after the three days and see if there is a difference_at least a visible one. I also quit watering my plants 3 days before harvest and got the same result. This last time I watered them right up to harvest then hung whole branches for almost two weeks in 60% humidity. I was concerned they would mold or something being wet when I hung them or too dry when I got back but lucky for me they were fine and cured well. The buds were more dense than before, but I'll never try that again_it was just too crazy not being there to check on them! This next time I'm going to stop watering the day I put them in the dark and then take them down to dry. That should be good balance, we'll see....

[DingusKhan]

I hung my current harvest, first half of Death Star in my veg closet with the lights going on and off because I had no idea about all of this. I took all that shit down, and will now do what you just said, DAAS.

[Locrian99]

I’m leaning towards for sure trying the dark. Hopefully the humidity doesn’t get too high, I see a pretty good jump during lights out and of course we are having our wettest week since last winter this week. Last two plants in the tent, so it’s an easy enough option. Drying I might do in a large cardboard box cut a few holes for air flow. No closet in basement and don’t really want to dry on main floor or upstairs around my son.

[greenforce]

I have never given this any real thought before but it absolutely rings clear now. Back in the day we harvested at night/early morning for stealth. Now that I am indoors, I usually harvest my plants first thing in the morning, trim, & hang so I can get it behind me. After reading through this thread I have already drawn up plans for a dark room with simple enviromentals. Thanks Campesino, your science checked, and sold ! I'm in.
This will allow me to free up space in the flowering chamber 2-3 days early. What's not to love ?
This is the first site for growers I have taken the time to participate in and now I wonder what took me so long. This forum is the sweet frosting on the all ready delicious cake. Thanks to all. G

[Vitreous]

Hey Locrian, I once wondered the same thing, let me help speed up your decision making from my experience. I say.. "No" not much difference, especially with resin production.
I have done both with the same strains on back to back harvests, 2 plants of White Cookies. both harvests yielded 12oz, @ 23% THC.
I would also like to add the plant that had no darkness continued to produce a little more weight, it was 1/2oz more than the plant in darkness.
But once they are cut, I keep them in cool dark room with very small fan for circulation. I also found it made no difference to the plant watering right to the last day or not watering for 2 days before cutting.
I am an avid data collector, so I document all my moves.

[D.A.A.S.69]

Your not the only one that collects data. My eyes tell me what's going on.I see more trichs when I put mine in the dark.

[Vitreous]

@D.A.A.S.69
Naturally your eyes are most important, Imagine being blind and feeling your way around cannabis plants, judging how sticky and stinky your fingers get. lol
When mine are in the dark, the trichs shine like white mountain tops, as opposed to staring at them during the day with light saturation. Keep in mind, keeping data stored in the head, certain details can be forgotten, hence the importance of journals and data columns.

[D.A.A.S.69]

Vitreous , my eyes are 20-20 ,,just cause,you see no improvements with your plants, tells me nothing, plus, I've been keeping journals from my huntin-fishin-pot growing for over 50years, plus I might add some things to my plants ,that you don't. Like really knowing how to wound or stress a plant, in the right way, that really helps trich production, that You don't do.
You stick with your ways, I'll stick with mine.And anytime ,that you want to compare
buds, just let me know, my good friend.
Ps, your couple of plants comparison, is really small, compare plenty next time, because we grow plenty outdoors where I live, an like I said, I don't have to go in there an feel around like you suggest, cause I got good eyes.
Lots of variables, that your not considering.
I didn't say it was a cure , especially if you don't grow your plants right. But we see, a little more by keeping them in the dark, a few days before harvest, no big explosion, by any means, but enough ,to justify it helps us. And we will continue doing the same, You don't have to,though, no one is forcing you.
Anyway, good luck, with your future crops.

[Campesino]

abadtrip

@ campesino Can u please direct me to the base of your findings because I have read scientific papers done in labs that say a dark period does nothing and light does not degrade thc. I would love to read the science u have because it contradicts everything I have been reading from the science community.

A couple sources to consider. I am still planning to put together a more thorough post on this, but time is limited.
Also, please share the "scientific papers" you mentioned!

You said "light does not degrade THC". This is the easiest claim to correct. See this Leafly article for example: https://www.leafly.com/news/cannabis...is-degradation

There does not appear to be clinical experimentation on dark periods before harvesting Cannabis. Well, there does not appear to be published info on them. Entirely possible that large growers have done the tests, but keep the results proprietary. The information I provided is the theory behind why it should work. You'll come across other theories online to explain it, and lots of circumstantial evidence on both sides. If you are looking for hard clinical data on this particular question I am afraid you will be disappointed.

That said, there has been research on other C3 plants, that supports the theory. In particular, I offer the abstract from the following paper on Spinach. It does not explore an extended dark period but rather the effect of time of day on harvest potency. They don't study extended periods of darkness on Spinach because (despite the pictures on many LED brochures) nobody grows spinach in a light sealed tent, so extending the darkness isn't really an option!

I am an educator and my use of the following conforms to fair use guidelines.

"Ascorbic acid, nitrate, and nitrite concentration relationship to the 24 hour light/dark cycle for spinach grown in different conditions"
Food chemistry, 01 May 2013, Vol.138(1), pp.382-8
Description
Nitrate, nitrite and ascorbic acid (vitamin C) concentrations were determined for spinach (Spinacia oleracea L.) over a 24 h period to determine if light intensity (including dark periods) at time of harvest impacts concentrations in raw vegetables. Nitrate, nitrate and ascorbic acid concentrations varied significantly over the 24 h period and appeared to be related to changes in light intensity. Light intensity at the time an experimental sample is collected may affect the concentration of some constituents that a researcher is studying. Also, nitrate and nitrite concentrations in raw spinach can be reduced by harvesting at the best time of day. The highest nitrate concentrations in spinach occurred in the darkjust prior to an increase in light intensity. Ascorbic acid was near its highest level for the 24 h period when the light intensity initially increased, then decreased to its lowest level around 3-6 h later.

[MadMike]

Very interesting info. I like the 'fair use' claim. Keep the research papers coming!

[Locrian99]

This is probably along the lines of defoliating. Some swear by it and some don’t. I guess just do what works for you in the end.

[Locrian99]

We should’ve germinated during the eclipse last year! Pop em in the rooter during totality! I was bar tending during it figured out when to start dark side of the moon so that eclipse was playing on the jukebox right at totality. You’d be shocked how many people were drinking at 8 am that day.

[DingusKhan]

Holy shit, Locrian99 you were pouring in the path of totality? Damn. Props, man.

[Locrian99]

Lol. I was opened the bar at 8 am that day I had people standing out front. Sat on the back patio to watch and any place else people could park in that little town. We were on the north end of totality