How to decrease THC level in harvest time?

Hi growers,
bcs I want sell legal CBD flowers, my target is 0,2%THC and lower.

  1. If I let plants longer time unlit trichomes will be brown - from THC will be CBN, so for my purpose is better cut them 7-10 days after normal harvest time?
  2. I can cut them one week early, but I get also lower amount of grams.
  3. Cut them 7-10 days later, than normalny, after 12 hours light, when THC level will be lowest and also rest of THC will be CBN?

What do you think? Any tips or ideas?


I want to preference this, I am no expert. I’ve heard from local hemp growers that THC increases with longer flower. CBD increases but THC also increases. They have to continually test the hemp early to make sure it does not “over mature” and make the growers THC content go over the allowed limit for CBD hemp. Does this make sense?


Just to verify, you are running a CBD type plant / pheno?

Three distinct types illustrated from potency testing of around 3K samples:

Here is a plot of strains that have THC tested to less than 1%:

And, further, strains that have shown a THC of less than (0.2%):


Nice graphs, it can show how high can be CBD in diferent strains with different THC levels, but not help me, with my question… And yes, I have CBD strain. Limit 0,2%THC (can be also 0,3%, but first is better).

What I rode is THC degrades to CBN (not CBD), when are trichomes amber. Also I know, than THC level is lower, when are trichomes clear and just few milky.

I just looking for somebody who tested in lab same strain in diferent phases or somebody who is sure in that… When is best time harvest CBD strain with lowest THC… I found some discussions, but also speculations…


Anyway… now my plan is cut plants in stadium, when trichomes will be clear and just few milky… I leave one plant until she will have all trichomes amber… then lab tests… it is not cheap, but I will be sure, if I dont find the right ansver somewhere esle (like here or Google) :slight_smile:


I think most of the stuff we’ve read about THC degrading into CBN later in flower is mostly unverified ‘stoner science’. I’d bet that the cannabinoid profile of any plant is pretty much exclusively determined by genetics. I think your best bet would be to grow lots of different phenos, get them tested, and then keep the suitable ones as mothers for future runs.


Yes, I will make this way with my regular seeds from breedind… Now I have clones from tested mother, they harvest this flowers when I wrote first time - clear trichomes 70% and 30% milky. stigmas a little brown.

I think the same thing what you wrote - depend on genetic, the best way is find the mother and the right procedure :slight_smile: so thx growers for consultation

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It’s actually verified science. It’s not subject to debate. THC degrades to CBN as a product of oxidation.


Yes I think so too… and CBD is same all the time, maybe little bit higher in old plant. Only one minus is, than old plants with all amber trichomes can get fungi (mold) faster…

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Hemp growers test their product throughout the flower process. Most CBD cannabis is grown with clones because of this reason. You cannot guarantee a seed will have low enough THC until you flower it and test it. Anyone who grows CBD cannabis (less then a certain % of THC legally) for profit will not look at how amber or clear the trichomes are (bro science in this industry). They will test it in a lab during the flower process. They will harvest when the THC test gets close to the max. This is something they do not push because they often have thousands or millions ridding on a crop. It is not worth hoping some of the THC will convert to CBN due to oxidation.


You can play with altering THC content in the ways you mentioned, but it is only going to sway it 10-30 percent at most. When we are talking about 0.2% that is not very much loss, and your CBD % will be affected by all of those methods. Most people pull early if they are trying to stay under for THC.

I have had similar ideas though, about spreading out flower under UV light or heat to degrade the THC. At the end of the day, it isn’t worth it; you should just find a cultivar that will test legal when grown and treated right. There are some CBD varieties compliant for smoked flower that are emerging (Soverign Fields claims a 13% CBD, <0.01THC).

Hemp is mostly grown from seed, due to the sheer scale. To grow for legal flower for CBD, @Tommy_McCain is correct that the best way to do it is find a clone with a good ratio (1:50 or greater), so that you can take it to full term and not go over THC %. This is exactly the reason CBG is becoming a huge thing for smoked flower next year, as there are CBG cultivars that will test legal when grown from seed. (Please see my thread here.)

from Potter, D. J. (2013). A review of the cultivation and processing of cannabis (Cannabis sativaL.) for production of prescription medicines in the UK. Drug Testing and Analysis, 6(1-2), 31–38


I understand. Thx for ansver. Just I am with open thinking and showing to the others my results… So maybe I have to stop and keep it for me… No, I am just joking :slight_smile: I always had great tasting models, made it with love and I am not afraid from rivals… Yes I want in the time build bigger company, maybe I will show resulst with less informations :smiley:

One test in my country cost 65€ (70$). And I dont know cheap and accurate machine for testing… Best what I found was some spectrometer from Israel And price was 4000€. So I can do only few test in one round. Also if I want test during flower time, resulst will come in 5-7 days delay…

Also I am fighting for increase level THC in hemp, like in Schiwtzerland - 1%THC… Now we have 0,3… I am in legalization group created by growers and politics, so I hope, than soon we will have good results :slight_smile: I think than 1 or 2 years and we will move…

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Where are you located?

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Within a week or two on the plant? Do all strains do it at the same rate and times? I’d love to see some actual studies on this.

Thank you for this graph. Thats what I need. Yesterday I spoke with my friend about CBG, so cross fingers, for your project :slight_smile:
And great inspirstion, maybe I ll try too some CBG strains… when it will be able to buy

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Adam Dunn said it best…Send it here, I’ll take all that THC & dispose of it in small controlled burns :joy:


:evergreen_tree: love me some CBD too