# Dark period before harvest



## RickWhite (Aug 9, 2009)

Most of us have head the hypothesis that there is a correlation between higher UVB light and THC production.

One of the main thoughts behind this is that weed from geographic areas with higher UVB is more potent and that the reason is to protect the plant from the damaging UVB rays.

Let's suppose there is merit to this notion. If this is so, it is likely that strains from this region have evolved genetically to produce more THC. But, we also know that UV light damages THC.

So, it might make sense that the way to optimize TCH levels is to grow a plant with high THC producing genetics and then turn off the lights for the last week or so before harvest.

The logic behind this is that evolution has programed the plant to produce high THC levels, but in the process the TCH is likewise degraded by the UV light it protects against.

If this logic holds, the best results would be obtained by allowing the plant to produce a genetically determined amount of THC with no UVB light decomposing that THC. In other words, you turn the lights off a week before harvest to minimize degradation by the UV but the plant continues to produce THC based on genetics.

Scientifically it makes more sense than supplying more UV light that we already know to be damaging to THC. It also makes sense that evolution of a population is more responsible for THC production than environmental factors placed on a single plant. This is basic genetic understanding. Evolution works on populations, not on individuals.

If 'm correct, it's best to turn off the lights a week before harvest.


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## Properlike (Aug 10, 2009)

RickWhite said:


> Most of us have head the hypothesis that there is a correlation between higher UVB light and THC production.
> 
> One of the main thoughts behind this is that weed from geographic areas with higher UVB is more potent and that the reason is to protect the plant from the damaging UVB rays.
> 
> ...


It works I've tried it with White Widow before in fact it is recommended with white widow during the ninth week to do so...I noticed significant crystal production over the previous week....why would any plant be any different?


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## RickWhite (Aug 11, 2009)

Properlike said:


> It works I've tried it with White Widow before in fact it is recommended with white widow during the ninth week to do so...I noticed significant crystal production over the previous week....why would any plant be any different?


I doubt they would. I think THC production is genetically pre-determined much more so than it is condition dependent and will occur on any healthy plant. Plus, I'm also quite sure it takes very little energy for the plant to produce it.


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## KP2 (Aug 11, 2009)

turning the lights off is an old trick, but i think the reason has been forgotten. you know how hydro plants have nice pretty dark green leaves at harvest? people shut the lights off to lighten the color of the buds. dark green turns to light green from lack of light, which is more appealing in a bag than extremely dark buds.


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## RickWhite (Aug 11, 2009)

Sounds like a good time to cut the lights is when you begin the flushing process. Plus, less chlorophyll means less lawn mulch smell.


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## jeebuscheebus (Aug 11, 2009)

So you are going to have the plants in 168 hours of continual darkness before you harvest?


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## chompy (Aug 11, 2009)

I think 24 to 48 hours is the standard procedure


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## sandmonkey (Aug 11, 2009)

I don't buy into this.

If indeed light (or UVB) is the cause for resin glands and thus THC production, then how would darkness increase it???

If anything I'd add reptile UVB lights to my grow room.


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## RickWhite (Aug 12, 2009)

sandmonkey said:


> I don't buy into this.
> 
> If indeed light (or UVB) is the cause for resin glands and thus THC production, then how would darkness increase it???
> 
> If anything I'd add reptile UVB lights to my grow room.


It comes from a good understanding of how evolution works. Environmental stress causes a change in populations, not in individuals.

People assume that because potent weed comes from areas of high UVB concentration that it is exposure to the light that makes them produce THC. It is just as reasonable (maybe more so) to attribute this to evolution and genetics rather than exposure of the individual specimen.

It is also just as likely that the THC produced by the plant is an expendable component with regard to the plant's reproductive success. Therefore the UVB could actually destroy THC rather than stimulate it's production.

More simply put - I'm betting the THC production comes from genetics and evolution much more so than environment. If this all holds, you could improve your strain genetics by actually killing 9 of 10 plants with excessive UV exposure and breeding the survivers. After several sets of offspring you should have a much more potent plant.

I know this all sounds complex and that's because it is. Especially, if you don't have a background in biology, evolution and genetics.

Anyway, if all that is accomplished is loss of chlorophyll it's worth doing. Anyway, I hope this makes some sense.


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## jeebuscheebus (Aug 12, 2009)

Still no answer...?

So you are going to have the plants in 168 hours of continual darkness before you harvest?


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## RickWhite (Aug 12, 2009)

jeebuscheebus said:


> Still no answer...?
> 
> So you are going to have the plants in 168 hours of continual darkness before you harvest?


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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## potsticker (Aug 16, 2009)

Could it be that areas with high UVb light get more light overall and that is why they produce more?


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## bushmang (Aug 16, 2009)

24 to 48 hrs worked best for me i did it on nlx once with and once with out and when i did it with the nugs put me on the couch more. 36 hrs is what i do


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## RickWhite (Aug 20, 2009)

So I was at my friends place and had a look at the plants after close to a week of no light soaking in Clearex.

What I observed was marked lightening of the leaves but not so much in the buds. More importantly, I noticed that the trichomes were significantly more milky when looked at under a 30x microscope. He has begun the harvest with no amber but a lot of very milky trichomes. According to Craventes the milky color correlates with peak THC. This crop definitely has far more milky color than the last and they are the same clones.


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## potsticker (Aug 21, 2009)

Trichomes are clear, then milky, then amber. Harvest around 60% amber for peak potency. I don't know who Cravente is but it sounds like he harvests a little early.


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## mindphuk (Aug 22, 2009)

potsticker said:


> Trichomes are clear, then milky, then amber. Harvest around 60% amber for peak potency. I don't know who Cravente is but it sounds like he harvests a little early.


I thought amber was degrading THC. You want to wait until there's a few amber to assure you have the majority of them in milky, high THC levels. That's what I have read.


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## matthew1 (Aug 22, 2009)

does this trick work for every strain or does it work better with a indica or sativa? I got 18 of them going now so i will deff try this process with one or two of the same strain to see if it works. thanks for the idea.


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## mindphuk (Aug 22, 2009)

RickWhite said:


> I know this all sounds complex and that's because it is. Especially, if you don't have a background in biology, evolution and genetics.


Evolution, schmevolution! You activist atheists can't stop shoving that crap down our throats everywhere you go, can you? 




j/k


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## RickWhite (Aug 22, 2009)

J. Craventes wrote the "Grower's Bible." He says to harvest once the trichomes become milky and that amber trichomes is a sign of THC degradation. IMO, I wouldn't wait so long as to see too many amber trichomes.

As far as which strains it works with I would assume all of them would be equally affected. Besides, even if there turns out to be the same level of THC, getting rid of some chlorophyll never hurts.


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## potsticker (Aug 22, 2009)

Well if it's in the bible it must be true! We're all entitled to our opinions however in my experience waiting for the amber results in a far more devastating high. I believe your milky theory only applies to pure sativas.


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## Brick Top (Aug 22, 2009)

potsticker said:


> Well if it's in the bible it must be true! We're all entitled to our opinions however *in my experience waiting for the amber results in a far more devastating high. I believe your milky theory only applies to pure sativas*.


The differing effects that come from trichome color changes are not limited in any way by a strain being a sativa or an indica or a cross that is dominant in one or the other. Of course you cannot turn a sativa high into an indica couch-lock body stone simply by letting the trichomes turn a darker amber and you cannot turn an indica couch-lock body stone into a cerebral sativa high by harvesting when most trichomes are milky white but in any case you can fine tune what you get by when you harvest and what trichome colors you have at the time. 
&#12288;
It is all based on personal preference in high or stone or a combination of each and of course whatever strain or strains are grown and how much fine tuning can be done by picking different trichome colors to harvest at.
 

Trichomes 

Trichomes are small appendages that look like hairs. They are produced by marijuana, and other plants. Female marijuana plants produce certain trichomes that are a rich source of THC. These trichomes can be found in their largest concentration on the buds. They start out clear, turn a milky color, then turn amber (light brown). 

The trichomes in picture 1 are clear. After the plant has flowered for a few weeks, the trichomes start to turn a milky color (picture 2). After a few more weeks, they will be totally milky in color. In the later stages of flowering, trichomes will turn to a light brown color (picture 3). The amount of time required to get to this point depends on the marijuana strain and the growing conditions. 

In picture 2 you can see the stems have started to turn from a clear color to a milky translucent color. *For maximum THC content *and a more cerebral and energetic high, harvest your plants when a majority of the trichomes on the plants in your garden are a fully milky translucent color. 

You can wait until most of the trichomes have started to turn amber, but the resulting marijuana will produce more of a sleepy body stone than it would if plants were harvested earlier. The trichome in picture 3 is about 90% amber, with just a trace of the milky translucent color it previously possessed. 

After the trichome is fully amber in color, the THC starts to degrade. This makes it very important to harvest marijuana at the time before a majority of the trichomes have attained a total amber color. If not, the marijuana will not be as potent as it could have been.


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## RickWhite (Aug 22, 2009)

The trichomes I saw after the long dark period were far more milky looking than that pictured.


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## mhg26 (Aug 22, 2009)

RickWhite I definitely understand what you are saying. I'm majoring in Biology so it definitely makes sense to me that a lack of UVB light would actually increase the plants THC. But on the contrary, some think that short exposures to marijuana plants makes the plant produce extra THC to protect itself because in nature THC is the chemical that cannabis uses to protect itself from UVB rays- sort of like melanin in humans


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## RickWhite (Aug 23, 2009)

mhg26 said:


> RickWhite I definitely understand what you are saying. I'm majoring in Biology so it definitely makes sense to me that a lack of UVB light would actually increase the plants THC. But on the contrary, some think that short exposures to marijuana plants makes the plant produce extra THC to protect itself because in nature THC is the chemical that cannabis uses to protect itself from UVB rays- sort of like melanin in humans


Of course, there are several threads on that. Either hypothesis could be correct. If milky color is an indicator of THC content I guess one could expose a single cola to a reptile bulb and compare to the other colas. Then of course there is the smoke test. But that's pretty subjective. And we don't know if milky color is a good indicator but I'm guessing it is. After the dark period these trichomes were notably more milky than previous clones taken from the same mother.

Perhaps someone using additional UVB will post about their trichome color.


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## 323cheezy (Aug 23, 2009)

elementry if u ask me 
my deer watson...
plants , species, aniomals.... all evolve...
over millions of years....
most evolution happens within the first 100 years of the species...

my understanding is that increased darkness promotes flowering .....
by tricking the plant into thinking fall and winter are coming...
as for trichs....
i always thought they may have come about due to pests....
the trichs may have been an evolutionary tool .... that allowed cannabis palnt to survive pest attack....
i could be wrong.... those are just assumptions....


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## mindphuk (Aug 23, 2009)

323cheezy said:


> elementry if u ask me
> my deer watson...
> plants , species, aniomals.... all evolve...
> over millions of years....
> ...


Actually there are some people that believe THC started out as protection from pests/UV light, but then there was a co-evolutionary development with man.


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## bball15bac (Aug 23, 2009)

would this theory hold true for auto-flowering plants. I ask because altough they only go through about 6-7 weeks of flowering. Would it maybe be better to keep them off for the last 48-72 hours?

~Smoke Blissfully, Life Is Good


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## Higher Education (Aug 23, 2009)

The problem I see with this is that although turning the lights off for such an extended period of time would cease the degregation of thc, it would also hinder the uptake and processing of essential carbohydrates since photosynthesis cannot take place in the dark. Doing this is the last few days of flowering might actually be counterproductive in terms if overall yield.

Also, what if the plants that produce more thc in areas of higher uvb radiation do so because the uvb radiation activates the particular genetics that make it possible? What if by taking away the uvb radiation in attempt to stop the degregation of thc has a counter effect and prevents the plant from activating the genetics neccessary to produce that extra thc in the first place?


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## RickWhite (Aug 23, 2009)

Higher Education said:


> The problem I see with this is that although turning the lights off for such an extended period of time would cease the degregation of thc, it would also hinder the uptake and processing of essential carbohydrates since photosynthesis cannot take place in the dark. Doing this is the last few days of flowering might actually be counterproductive in terms if overall yield.
> 
> Also, what if the plants that produce more thc in areas of higher uvb radiation do so because the uvb radiation activates the particular genetics that make it possible? What if by taking away the uvb radiation in attempt to stop the degregation of thc has a counter effect and prevents the plant from activating the genetics neccessary to produce that extra thc in the first place?


When you have reached harvest time growth has pretty much ceased and THC production has peaked. It is possible that the plant will stop producing more in the absence of light or it may produce even more. Remember the plant does have a mechanism in which longer dark periods stimulate THC production, this we know to be true.

You could be correct but if this is the case it would be best to leave the lights on continuously for the last few days of growth.

In the end there are a number of hypothesis that could be correct. I am just putting together the things I am reasonably confident in.

A) UV light degrades most chemical compounds.

B) THC is largely a result of genetics more so than environment. Obviously the best grow hemp would just be hemp and OG Kush would still be potent even if growth was slow and yields small.

C) Longer dark periods signal the mechanisms that produce buds and THC.

D) Milky trichomes signify high THC levels and I have observed a marked increase in milky trichomes of plants kept in the dark for several days.

Other considerations:

If you are getting ready to flush the plant and harvest you are killing the plant anyway so why not flush in the dark. Also, promoting loss of chlorophyll is good.


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## mhg26 (Aug 23, 2009)

Higher Education, while some of your points may be true, the dark period is essential for plants to complete the calvin cycle. In this cycle the plant takes the light and energy from the light cycle and uses it to create sugars for growth- So I would say although the light is very important so is the dark.


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## That 5hit (Aug 23, 2009)

what of the revers
can i leaves the lights on for a week then harvest sences i will be drying in darkness anyways for 5-7 days
leave the lights on for the last 5-7 days then harvest what of this


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## Higher Education (Aug 23, 2009)

RickWhite said:


> When you have reached harvest time growth has pretty much ceased and THC production has peaked. It is possible that the plant will stop producing more in the absence of light or it may produce even more. Remember the plant does have a mechanism in which longer dark periods stimulate THC production, this we know to be true.
> 
> You could be correct but if this is the case it would be best to leave the lights on continuously for the last few days of growth.
> 
> ...


Rick, I agree with what you are proposing, just not on such a drastic time scale. Yes, when you reach harvest growth has ceased and so has thc production, but you are proposing turning the lights off a week before if I'm not confused. I believe there are exceptions to a lot of your points too though. The first thing you said would be obviously as counterproductive as what I am supposing your idea over such an extended time period to be. The plant would not be able to use the ATP and NADH it has worked hard at producing during the day. Now, for your lettered points:

A. I agree completely!

B. If environment wasn't that significant, then we wouldn't be debating over how to alter it to increase thc right now.

C. I believe this is true to an extent. I think the inverse is more true, shorter light periods induce budding and thc production, which in turn, means longer dark periods, but not to the extent that where there is not enough light to complete one circadian rythm.

D. I agree!

I also believe what you are suggesting about the chlorophyll would be a wonderful idea. The drying and curing process could possibly be much quicker. I am just not sure on the time scale of your proposal though, convince me otherwise.





mhg26 said:


> Higher Education, while some of your points may be true, the dark period is essential for plants to complete the calvin cycle. In this cycle the plant takes the light and energy from the light cycle and uses it to create sugars for growth- So I would say although the light is very important so is the dark.


Well said, but remember what we are suggesting here is to take away one of neccessary elements to complete the calvin cycle.


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## mhg26 (Aug 24, 2009)

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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## mindphuk (Aug 24, 2009)

Here's where I think you are thinking about this incorrectly. If the time to harvest is x weeks, then shutting the lights down two weeks early will decrease the time to harvest by two weeks. IOW, the time specified is based on when the plant is mature in bud and weight density otherwise they would judge the strain to have finished earlier. So ending your light cycles too early will stop the photosynthesis cycle and carbohydrate and THC production will grind to a halt. 

Taken from Marijuana Botany by Robert Clarke

Factors Influencing THC Production

Many factors influence the production of THC. In general, the older a plant, the greater its potential to produce THC. This is true, however, only if the plant remains healthy and vigorous, *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. Warm temperatures are known to promote metabolic activity and the production of THC. Heat also promotes resin secretion, possibly in response to the threat of floral desiccation by the hot sun, Resin collects in the heads of glandular trichomes and does not directly seal the pores of the calyx to prevent desiccation. Resin heads may serve to break up the rays of the sun so that fewer of them strike the leaf surface and raise the temperature. However, light and heat also destroy THC. In a drug strain, a bio-synthetic rate must be maintained such that substantially more THC is produced than is broken down. Humidity is an interesting parameter of THC production and one of the least understood. Most high-quality drug Cannabis grows in areas that are dry much of the time at least during the maturation period. It follows that increased resin produc. tion in response to arid conditions might account for increased THC production. High-THC strains, however, also grow in very humid conditions (greenhouses and equatorial zones) and produce copious quantities of resin. Cannabis seems not to produce more resins in response to dry soil, as it does to a dry atmosphere. Drying out plants by with-holding water for the last weeks of flowering does not stimulate THC production, although an arid atmosphere may do so. A Cannabis plant in flower requires water, so that nutrients are available. for operating the various bio-synthetic pathways.

There is really no confirmed method of forcing increased THC production. Many techniques have developed through misinterpretations of ancient tradition. 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). Impaling with nails, pine splinters, balls of opium, and stones are clandestine folk methods of promoting flowering, taste and THC production. However none of these have any valid documentation from the original culture or scientific basis. Symbiotic relationships between herbs in companion plantings are known to influence the production of essential oils. Experiments might be carried out with different herbs, such as stinging nettles, as companion plants for Cannabis, in an effort to stimulate resin production. In the future, agricultural techniques may be discovered which specifically promote THC biosynthesis.

In general, it is considered most important that the plant be healthy for it to produce high THC levels. The genotype of the plant, a result of seed selection, is the primary factor which determines the THC levels. After that, the provision of adequate organic nutrients, water, sunlight, fresh air, growing space, and time for maturation seems to be the key to producing high-THC Cannabis in all circumstances. Stress resulting from inadequacies in the environment limits the true expression of phenotype and cannabinoid potential. Cannabis finds a normal adaptive defense in the production of THC laden resins, and it seems logical that a healthy plant is best able to raise this defense. Forcing plants to produce is a perverse ideal and alien to the principles of organic agriculture. Plants are not machines that can be worked faster and harder to produce more. The life processes of the plant rely on delicate natural balances aimed at the ultimate survival of the plant until it reproduces. The most a Cannabis cultivator or researcher can expect to do is provide all the requisites for healthy growth and guide the plant until it matures.

Flowering in Cannabis may be forced or accelerated by many different techniques. This does not mean that THC production is forced, only that the time before and during flowering is shortened and flowers are produced rapidly. Most techniques involve the deprivation of light during the long days of summer to promote early floral induction and sexual differentiation. This is sometimes done by moving the plants inside a completely dark structure for 12 hours of each 24-hour day until the floral clusters are mature. This stimulates an autumn light cycle and promotes flowering at any time of the year. In the field, covers may be made to block out the sun for a few hours at sunrise or sunset, and these are used to cover small plants. Photoperiod alteration is most easily accomplished in a greenhouse, where blackout curtains are easily rolled over the plants. Drug Cannabis production requires 11-12 hours of continuous darkness to induce flowering and at least 10 hours of light for adequate THC production (Valle et al. 197. In a greenhouse, supplemental lighting need be used only to extend daylength, while the sun supplies the energy needed for growth and THC biosynthesis. It is not known why at least 10 hours (and preferably 12 or 13 hours) of light are needed for high THC production. This is not dependent on accumulated solar energy since light responses can be activated and THC production increased with only a 40-watt bulb. A reasonable theory is that a light-sensitive pigment in the plant (possibly phytochrome) acts as a switch, causing the plant to follow the flowering cycle. THC production is probably associated with the induction of flowering resulting from the photoperiod change.

Cool night temperatures seem to promote flowering in plants that have previously differentiated sexually. Extended cold periods, however, cause metabolic processes to slow and maturation to cease. Most temperate Cannabis strains are sensitive to many of the signs of an approaching fall season and respond by beginning to flower. In contrast, strains from tropical areas, such as Thailand, often seem unresponsive to any signs of fall and never speed up development.


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## mindphuk (Aug 24, 2009)

Peer review studies have shown elevated levels of THC after exposure to UV. I agree with you that UV should be damaging and breaking down THC, but I suggest that maybe the THC production out paces the breakdown. Remember, it can take years to degrade THC with light but the plant produces a majority of it in 8-14 weeks. Also, some compounds, sunscreen comes to mind, scatter UV light, others absorb it and re-radiate it as heat. Keep in mind the many cannabinoids beside THC, they could all be working in conjunction as the plant's natural sunscreen, some absorbing, some scatter, etc. 

Here's the abstract of at least one study showing an increase in THC after exposure to UV.




UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES

John Lydon* 2 Alan H. Teramura 1 C. Benjamin Coffman 3 1 Department of Botany, University of Maryland, College Park, MD 20742, USA 2 USDA-ARS, Southern Weed Science Laboratory, P.O. Box 350, Stoneville, MS 38776, USA 3 USDA-ARS, Weed Science Laboratory, AEQ. I, Beltsville, MD 20705, USA 
*To whom correspondence should be adressed. 

Copyright 1987 American Society for Photobiology

*ABSTRACT*


The effects of UV-B radiation on photosynthesis, growth and cannabinoid production of two greenhouse-grown C. sativa chemotypes (drug and fiber) were assessed. Terminal meristems of vegetative and reproductive tissues were irradiated for 40 days at a daily dose of 0, 6.7 or 13.4 kJ m-2 biologically effective UV-B radiation. Infrared gas analysis was used to measure the physiological response of mature leaves, whereas gas-liquid chromatography was used to determine the concentration of cannabinoids in leaf and floral tissue.
There were no significant physiological or morphological differences among UV-B treatments in either drug- or fiber-type plants. The concentration of &#916;9-tetrahydrocannabinol (&#916;9-THC), but not of other cannabinoids, in both leaf and floral tissues increased with UV-B dose in drug-type plants. None of the cannabinoids in fiber-type plants were affected by UV-B radiation.
The increased levels of &#916;9-THC in leaves after irradiation may account for the physiological and morphological tolerance to UV-B radiation in the drug-type plants. However, fiber plants showed no comparable change in the level of cannabidiol (a cannabinoid with UV-B absorptive characteristics similar to &#916;9 THC). Thus the contribution of cannabinoids as selective UV-B filters in C. sativa is equivocal.


(Received 29 August 1986; accepted 24 February 1987)


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## Higher Education (Aug 24, 2009)

Mindphuk, I am too tired to read your entire post, but I am completely with you on the influence uvb has on thc production. The most potent outdoor weed in the world comes from areas that have high uvb concentrations. The science behind this is not completely understood, but marijuana man does a great job explaining what is known in this youtube video. I am so convinced, I am going to buy a uvb light from a reptile store. Everyone watch this!

http://www.youtube.com/watch?v=IPcpt3Be28o

I am sorry to diverge from your hypothesis Rick, but I think this information in this video can be beneficial to us all.


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## stonurse (Aug 24, 2009)

lights off...this needs good timing..and differs in every strain..specially sativas...so observe your girls carefully... =)


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## 323cheezy (Aug 24, 2009)

so ive been doin 11light ... 13 dark since my 3rd week of flower .... to lower heat and electric bill....
mostly cause after 10 hrs of my 400 being on ..... it gets hot ....like about 86-90 degrees...
i think that his debate helped us shed light on this mystery ....however
i believe ... without fact or resource..... just using my convientional wisdom......
that the more light a plant get the more energy is produced .....
but does the plant really need 12 hrs..... 
and is 10hrs gonna really stop production.....
i dont think thats the case.... 
yeah it might not producce as much energy....
but less hrs of light tellls the plant fallscoming time for budding....
furthermore in nature in the fall light cycles can go from aprox(depending where u live)
from 14hrs of light in summer ....to 10hrs in the fall to winter periods.....
that seeems natural ... in nature it not 12/12 the whole flowering time.....
Moving along ... ive seeen many outdoor grows that only get about 8 to 10 hrs of direct sun.....
and the plants still grow nicely.... 

so should i be worred that because my plants only get 11hrs of light thatll theyll stop producing as much as they should?????


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## RickWhite (Aug 24, 2009)

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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## mindphuk (Aug 24, 2009)

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.


Then I didn't understand. If you wait until harvest to shut off the lights then flush, how is that going to be better than just harvesting and drying? They don't get light while drying or curing so it will be essentially the same except if you keep them alive for 2 more weeks, that extends the time until it is ready to smoke and I doubt it will do anything more than if you properly flushed before hand. 

Please don't try to claim that a paper is invalid just because researchers have to publish. The very fact that it passed peer review is enough to take it seriously. Sure, results need to be confirmed but this study was 1987, and I don't have access to the most current botany journals, but I would bet money that this study has already been replicated. The fact that this was an actual scientific study in a refereed journal makes it more compelling than some guy on a weed forum with a hypothesis and who's attempting to compare THC levels by trich color and smokability alone without performing an actual assay. Sorry but it is pretty damn arrogant of you to criticize a study by Dr. John Lydon, a preeminent plant physiologist at the same time you want us to take you seriously yet you don't have any substantial evidence to back up your claims. 

If you want to see the full study, order a reprint or call Dr. Lydon and ask him to send you one. While you are at it, you can ask him for any additional studies he can find on the subject. I bet he'd be more than happy to comply.


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## Higher Education (Aug 24, 2009)

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


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.
> 
> ...


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.


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## RickWhite (Aug 25, 2009)

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.


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## ottertalkn (Oct 25, 2009)

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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## ebbnflow (Oct 26, 2009)

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?
> ...


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.


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## POLARIS01 (Oct 26, 2009)

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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## RanTyr (Oct 27, 2009)

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


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.


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## Twistedfunk (Oct 27, 2009)

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.


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## KP2 (Oct 27, 2009)

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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## Twistedfunk (Oct 27, 2009)

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.


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.


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## Old Fat Dude (Oct 28, 2009)

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 !!!


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## ottertalkn (Oct 28, 2009)

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


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## P. STONIE (Oct 28, 2009)

Smoke crack!!!


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## YankeeBurner (Nov 6, 2010)

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.


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## DecimateForce (Nov 24, 2010)

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.


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## SOGfarmer (Nov 25, 2010)

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.


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## JenkemBombs (Mar 4, 2011)

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.


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## Uncultivated (Mar 6, 2011)

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.


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).


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## dannyboy602 (Mar 11, 2011)

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


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