Dark before harvest

I've heard a lot of people say they leave their plant in darkness for the last 24 to 48 hours before Harvest I was wondering what the purpose of this is

Some say it increases thc production. Others say a myth. High Times on harvesting doesn't mention darkness, but a good flush.

I'm sure others will tune in. For us, good flushing (water the last 2 weeks) and drying out the soil before chopping.

Yes I'm going to flush them I have a tds meter I will use for the first time, I just got it, I'm going to flush with 10 gallons of water and test the run off. What's a good avarge ppm after flushing. Also I have a jewlers loop to check the tricombs and I was just wondering when the best time to harvest to help give a nice head high because I've seen a little on the subject but not much.

Old wives tale. Cannabis doesn't get a magic 24-48 hours of dark in nature. Might as well turn it upside down and boil the roots to get the extra THC...

Newbie95 said:

I'm going to flush with 10 gallons of water

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Yikes...

well it obviously doesn't get a magical 24 to 48 hours of darkness in nature that wasn't the question I was wondering what the purpose of doing it inside was. thanks for your aware airbud

CrossBones said:

Yikes...

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Between 3 plants

I'm going to give one a week dark before harvest. Just because I'm curious. I also gave it 3 days dark before flower already. Again, curious. I'll compare two side branches, one harvested normally the other with a week of dark.

Nature shmature.

For anyone curious about 72 hours dark before flower it didn't hurt it, slow it, stunt it, herm it and it didn't speed it up, it did jack and shit.

WelderDan said:

Old wives tale. Cannabis doesn't get a magic 24-48 hours of dark in nature. Might as well turn it upside down and boil the roots to get the extra THC...

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Lol or maybe hook a car battery up to it and shock it into making more thc.

Newbie95 I highly doubt there's anything to it if there was it'd be standard practice everywhere. Flushing and harvesting when the trichomes have the correct ratio of cloudy to amber heads is all that you need to be worried about. Good luck man

Newbie95 said:

I've heard a lot of people say they leave their plant in darkness for the last 24 to 48 hours before Harvest I was wondering what the purpose of this is

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Perhaps nothing more than an old wives’ tale; however, harvesting during the dark cycle isn’t.

I do it more so out of routine than anything else. Running a multi-strain garden from seed it’s easier to remove plants for darkness to then chop later outside the flower room instead of potentially disrupting light cycle to chop a plant or two. Additionally, the "dark room" is also maintained at a much lower humidity than the flower room.

Following quotes are from High Times:

"Lowering the humidity in the room on that last night before harvest morning will ensure increased resin production, without having to let the medium go bone-dry first. Additionally, some growers like to subject their gardens to prolonged dark periods of up to 24 hours just before cutting, claiming they notice spikes in resin production. This is all right as the low humidity will cut down on light uptake anyway, plus it helps to make sure liquid foods within the plants drain down to the root zone."

What time of day to harvest?

"Timing the harvest is Paramount to the final quality. Harvest your precious buds in the dark, just before the lights normally come on. If possible, do not allow the plants to see direct light as long as their roots are attached. Direct light on a plant will draw up stored starches and sugars from the root system. During the nighttime hours, our ladies are busy storing food down in their root system that they made during the daylight hours. During “lights out,” starches and sugars produced by photosynthesis during the day drain downward to the roots. Knowing this, it is easy to figure out that you want to cut your plants away from the roots before the lights come on, when food moves back upward into the buds. Outdoor herb is often harvested during the daytime hours and the result is a harsh, difficult burn and an extra long cure. The starches and sugars present in daytime-harvested herb act like fire retardants—not the effect we’re looking for. In addition to tasting and burning bad, these fire retardants also change the chemical make up of the smoke you’re ingesting. This means that the THC, cannabinol, cannabidoil and other active cannabinoids can’t burn at the perfect temperature to get you properly high because they haven’t properly converted to their psychoactive forms."

The excerpts from HT were just the most readily accessible, but I have read more "technical" writings over the years about the importance of a night time harvest - so it's doubtful a couple days darkness hurts anything. But does it increase THC? You'd have to run clones and harvest accordingly to submit samples to a lab. I look a plant over before putting into dry darkness and feel that resin often does increase by the time I chop - but I could just be really high!

That’s 48 hours of light down-time , fuck that... the next ladies could be using that growroom.
I like to repot and refil the room as soon as the last bud is hung

Was reading an article about a longtime Canadian breeder (Dr. Atomic) and a claim he made therein reminded me of this thread. Here’s what he said:

“These plants were left in darkness for three full days before being chopped down. Cannabis plants react to an extended absence of sun or light with the realization that frost/death is imminent, and pump out a lot of resin in a sort of panic. They know that their life is soon terminated so they try to attract pollen in a last gasp to get fertilized. I believe these last three days of resin production contain the most potent cannabinoids.”

The article was from 2006, so maybe his thoughts are different today, maybe not. Wonder if science has shown one way or the other...

IMO, it's nonsense most likely generated (again) due to slightly less than ideal flowering conditions. His plants appreciated the break and rewarded him for it.

Good find though, as it documents how some of this line of thinking was spread. I too would like to hear their opinion today as well.

Shmavis said:

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Thank you for your messages Shmavis. I found them well articulated and helpful. You put it very nicely that you do not have info on the subject but are repeating what you have found out from good sources.


As said, very helpful and well shared information - Thank you kindly

Shmavis said:

Perhaps nothing more than an old wives’ tale; however, harvesting during the dark cycle isn’t.

I do it more so out of routine than anything else. Running a multi-strain garden from seed it’s easier to remove plants for darkness to then chop later outside the flower room instead of potentially disrupting light cycle to chop a plant or two.

"Timing the harvest is Paramount to the final quality. Harvest your precious buds in the dark, just before the lights normally come on. If possible, do not allow the plants to see direct light as long as their roots are attached. Direct light on a plant will draw up stored starches and sugars from the root system. During the nighttime hours, our ladies are busy storing food down in their root system that they made during the daylight hours. During “lights out,” starches and sugars produced by photosynthesis during the day drain downward to the roots.

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This is why I do it not for increased resin production. It's not a strict 24hrs anyway. My lights come on close to midnight and I don't want to start chopping at midnight so I switch the lights off until the next morning.

Iamnumber said:

Thank you for your messages Shmavis. I found them well articulated and helpful. You put it very nicely that you do not have info on the subject but are repeating what you have found out from good sources.


As said, very helpful and well shared information - Thank you kindly

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You’re welcome. Thanks for the kind words. And yes, (practical) anecdotal evidence is all I have to point to. Just as deniers have nothing but opinions to deny with.

When we consider how a plant goes hermi in an attempt to preserve itself, it doesn’t seem too much of a stretch to think that it would pump out extra resin under such conditions (extended dark period) to attract pollen to get fertilized, as claimed.

It’s interesting, and something I have done for many years but admit I have questioned it from time to time.

insomniac_AU said:

This is why I do it not for increased resin production. It's not a strict 24hrs anyway. My lights come on close to midnight and I don't want to start chopping at midnight so I switch the lights off until the next morning.

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Thanks for sharing your experience. You’re getting at the gist of what I was trying to get at. This is the New Growers forum and even if new growers don’t give an extended period of dark before chopping, they should strive to chop before lights on. There is sound reasons for doing so.

If you want your weed to taste like the dirt/res it was grown in harvest at day. If you want your weed to taste like weed harvest at night. Taste buds required to make this determination.. Most growers don't have em apparently.

Plants pull nutes during the day and use them at night. All your starches and proteins will be converted, the low temps alone increase terps.. There's no reason not to harvest before lights on. It's goin to knock time off your cure at the minimum.

I have some thoughts for and against this:

Carbon assimilation is done best in the light. Stomata actively open and capture CO2 when light and heat are creating negative pressure, thus this the best opportunity for stomata to be open. In the dark, stomata are closed but porous- however, not even a percent of the activity when light is present. 50% of PAR is absorbed in the light becoming ~2% biomass. What might you think that percentage is in the dark?

That CO2 becomes CH2O becoming pyruvate to fuel TCA and mevalonate pathways which employ/metabolize root exudates and the excretions in our substrate and rhizosphere- ultimately becoming the prenoids/hydrocarbons which are the glands of our glandular trichomes. (There are a thousand more steps in there, but that's basically the frame...)

You can't get to frost/resin without light. I'm not saying a plant doesn't metabolize in the dark but the sort of negative pressure the light and heat provide are just as important as your nutrients, water, water use efficiency, etc. Preservation tactics would be employed and executed by the pericarp and endocarp cells of our bud- but guess what? pericarp cells also have stomata and they have to be open as well. If they were closed for a few days, how could these cells do anything remotely preservation like, let alone think about giving back frost, which costs the plant tremendously in terms of sugar or ATP/rubisco usage?

My point For is less.... pointed- when we go to cure, our enemies are heat, light and air- correct? Maybe the less light and heat you deploy on a standing plant, the less trichomes you destroy before harvesting? Or perhaps at a different angle of acceptance, or no angle of acceptance, of light- we perceive a difference in aesthetic quality?

Cheers, my friends!

And also, to clarify: metabolization in the dark. Creation of sugars is not light dependent; I just mean to point out the assimilation in the process. How can we have more production when our assimilation is capped by the lack of light, if you see what I mean...The splitting of water and the reduction of CO2 have to take place simultaneously, so that can only happen in the light.