Dark period before harvest

mhg26 said:

Yes I know I just realized that for the calvin cycle to even take place- first the light cycle has to occur lol. But I think you and Rick definitely both have a lot of good points and I'm really enjoying conversing the science of it with you

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Thank you, I can always appreciate someone who wants to learn more!

RickWhite said:

First, I would like to see the actual studies, how they were conducted and what the actual data was.

Second, I'm not suggesting turning off the lights before the buds are fully mature. I am suggesting allowing the buds to fully mature and then shutting them off for several days. I highly doubt runing a 10 hour light cycle as opposed to a 12 hour life cycle makes much difference in THC production.

One thing you always need to be careful of is citing a single study. In university science department there is a concept known as "publish or perish." This essentially means that if an aspiring professor wants his career to survive he had better come up with something to publish. Again, I would like to see for myself how those studies were conducted and what the actual data is. A lot of times a researcher will publish something calling it an "increase" but when reviewed it shows that the "increase was within the margin of error of the study.

What I observed (granted just with a 30x microscope) was a marked increase in the milky color of trichomes. The milky color is no doubt caused by the presence of something scattering light. Whether or not it's THC I don't know.

But, you could also do both. You could use additional UVB exposure up until harvest time and then flush the plants in the darkness. It seems unlikely to me that the plant will slam on the breaks with regard to THC production the moment the lights go out. That's kind of like saying the minute you stop eating your body begins muscle wasting. The plant will still have ATP stores that contain a significant amount of energy - I'd be willing to bet THC production is still possible.

But again, if light is so crucial to THC production wouldn't it be better to leave the lights on 24 hours a week before harvest?

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I am going to search my academic databases for some more studies that pertains to this matter when I have time Rick, being I am about to start school back myself. I wouldn't dismiss the credibility of mindphuck's article so quickly though. One academic study is less credible than five, but still credible. I doubt Dr. Clarke had any biases in his research about how he thinks cannabis should produce thc, that would be silly, and furthermore unintellectual of him.

Your suggestion of waiting for the buds to become fully mature, as opposed to starting the last week, intuitively seems problematic too. It seems as if once the buds have already fully matured then they would start declining. I don't see how the non-existence of light would interfere with this declination, being it's part of cannabis' natural life cycle.

Also, no one is implying that the light period is significantly more important than the dark period, just the fact that it is significant.

Researchers post BS studies regularly. I'm not saying that study is BS - just that I'd like to see it. If you have access to such a database see if you can copy the full text and post it.

Allowing the buds to fully mature and then giving them a few days of darkness will not degrade THC as there is a large enough window for harvest. And there is dissagreement over when to harvest anyway. Again, I have noted significantly more milky color after the dark period.

I've become more confused reading all this. I'm a newbie to hydro, been growing soil based for awhile. I guess I'm going to pose a simple question that could have a complex answer, but all I'm really looking for is some practical guidance. So here I go...

1. When should I flush my solution prior to harvest?
2. After the flush, should I add nutes back into a new solution, leave the plant in a new flush solution, or replace solution with plain old water?
3. How long do I wait to harvest after I flush?
4. Now the whopper based on this thread, does leaving the lights off for a day or three prior to final harvest get me anything from THC production perspective, or is it better to just keep with the 12/12 and enjoy what I have.

Thanks guys. The knowledge you folks are bustin on this thread is way beyond my understanding.

You help is greatly appreciated.

ottertalkn said:

I've become more confused reading all this. I'm a newbie to hydro, been growing soil based for awhile. I guess I'm going to pose a simple question that could have a complex answer, but all I'm really looking for is some practical guidance. So here I go...

1. When should I flush my solution prior to harvest?
2. After the flush, should I add nutes back into a new solution, leave the plant in a new flush solution, or replace solution with plain old water?
3. How long do I wait to harvest after I flush?
4. Now the whopper based on this thread, does leaving the lights off for a day or three prior to final harvest get me anything from THC production perspective, or is it better to just keep with the 12/12 and enjoy what I have.

Thanks guys. The knowledge you folks are bustin on this thread is way beyond my understanding.

You help is greatly appreciated.

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Really I would stay stick with 12/12 unless you have unlimited time and money to research. If you just want good consistent bud go with 12/12. Also flush 1 full week before harvest, i recommend using Advanced nutrients final phase. Other than the final phase if you put it in you will only be running pure phed water through your system for the whole week up until harvest, no nutrients. This was an awesome disscusion though and i hope someone researches this soon.

a plant will only live for 72 hours without light so before i cut the plants are in the dark for 72 hours

POLARIS01 said:

a plant will only live for 72 hours without light so before i cut the plants are in the dark for 72 hours

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The logic is that you will force the weed to consume all of it's energy stores. This makes for a slightly more potent (per weight), smooth and tasty smoke.


Edit: Just wanted to clarify the pro dark-period point of view.

I put my girls in darkness for the last 72 hours. They have the potential to increase THC production by a possible 5-30% in that time period. 72 hours is the longest a plant can produce without light. This also (as others have pointed out already) is the best way to begin curing before you even harvest! THC breaks down during the day in the light and rejuvenates during the dark period. Obviously this is more true in some strains than others and the results may very but as far as a dark period before harvest to ensure that you have the sweetest buds around (and you never have to flush), well..you can take that home with you and keep it. Its yours now. I recommend you put it to good use though.

you know what's funny? this was actually started to lighten the color of the buds, giving that limey green look.

imo, this does absolutely nothing to potency, pro or con. it does lighten the color, whether green or purple.

KP2 said:

you know what's funny? this was actually started to lighten the color of the buds, giving that limey green look.

imo, this does absolutely nothing to potency, pro or con. it does lighten the color, whether green or purple.

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yeah that's good, you don't want chlorophyll but not all strains increase potency and in the ones it does the results vary greatly between pheno's. Do it for the cure because you almost always want to harvest any herb/spice after a sufficient dark period. Also, THC degrades in the sunlight and regenerates during the dark phase so harvesting mid day = bad idea. These aren't opinions im giving you here.

I want to thank everyone who is involved in this discussion.....

To Quote Robert Clark ...

THC production requires the proper quantity and quality of light. It seems that none of the biosynthetic processes operate efficiently when low light conditions prevent proper photosynthesis. Research has shown (Valle et al. 197 that twice as much THC is produced under a 12-hour photoperiod than under a 10-hour photoperiod.

I was wondering if one increased the photoperiod by 1 or 2 hrs durring the last week or so of flowering (when using 12/12 regiment) would positively affect THC production ?

Perhaps then to implement the extended "Dark Period"....

I also appreciated the info :

In Colombia, farmers girdle the stalk of the main stem, which cuts off the flow of water and nutrients between the roots and the shoots. This technique may not raise the final THC level, but it does cause rapid maturation and yellow gold coloration in the floral cluster (Partridge 1973)

I always thought that Colombian Gold was real pretty, may just have to try that just for fun !!!

Thanks to all of you. I have the direction I need. Looking forward to harvest in 2 weeks.
Thanks again, and great advice!

Smoke crack!!!

My friend's too...they are milky as hell with limited amber trichs....seems to be taking forever...he wants some couch lock from it...weather has been chilly, around 40 and unpredictable. Nature did the flushing the last 2 weeks too along with a good ph'ed soaking.. Amber trichs are taking forever.

I usually give my plants 1-2 days of darkness before harvesting. I do believe that it forces the plant to use up more energy reserves to create the sticky goo we all love. However, I mostly do this because it takes 2 days for me to harvest everything and I'd rather save the $ in electricity.

For maximum THC production, I use this logic:
During the last weeks of flowering, the plant knows that it's life-cycle is coming to an end, so the plants naturally wants to preserve itself for as long as possible. It does this by creating a water proof goo around itself (THC) so the plant doesn't dry out as fast and it can preserve its fruit. Because of this, I think it is more important to drop humidity as low as possible (usually 20-30%) in the last weeks of flowering.

Moreover, I believe that the majority of the THC production comes from the curing process. Once the plant is cut and no more water is available the buds really begin to crystal up. During the drying process most of the water is evaporated out of the buds. The buds usually still have an earthy or grass like smell. Once dry, the curing process begins where I really see the buds crystal up and start to give off that wonderful potent aroma. I do this by placing the dry buds in a glass jar that I burp every so often. During this process, water is still evaporating out of the buds, but not as fast as when they were drying. This slower drying process (curing), is what I believe really gives true potency to the buds; remembering that the buds are still trying to produce as much goo to slow down the evaporation of water. I keep the jars cool and in a dark cabinet. During this time, the remaining active chlorophyl that gives the grassy smell goes away. I'll continue the curing process for 8-12 weeks, before I feel there is diminishing return of crystal production. It's not like I'm not smoking it during this time though.

You know that you've cured your buds well when they leave only a white ash after smoking them. Black ash means there is still lots of nutrients in the buds.

Here's a good little tip. Aside from darkness fo the last week of the grow cycle, make sure when you harvest your plants is is before the lights are turned on. Alot of the nutrients and salts and bad tasting stuff trickles down into the roots at night and then when the lights are turned on they start sucking everything back up. Better tasting smoke. Walah.

I figured I'd just bring back a old thread from the grave of threads I found on google about this damn subject rather then starting a new one.

Can anyone, without referring to "cannabis science" and only from true experience, tell me whether or not 2-3 days of complete darkness before harvest will increase potency?

If it doesn't, what could 2-3 days in complete darkness hurt? It could only help right?

Nother question, would flushing with water and oolong tea+sugar right before harvest increase potency, bud size, or make the taste/smoke better/smoother?

Thank you in advance for any and all replies that are helpful.

RickWhite said:

I haven't counted the number of hours. But basically I figure on about a week. Of course this will be flushing time as well.

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Correct me if I'm mistaken, but with no lights, there won't be any photosynthesis going on, hence no nutrients used, which would render your flush meaningless. I would think that you'd flush before turning off the lights (much like when using the restroom).

Very interesting thread. I'm growing WW and will try your advice.
One week/no light, correct?