The Dude Grows Show

Dark Period Before Harvest

I’ve seen a lot of people say they put their plants into a dark period before harvest. I wasn’t sure if it was “Bro Science” but last week DGC posted a video called “Proper Flush for Connoisseur Quality Cannabis” and Dude says he shuts off the lights for a 3-day dark period before harvest. 

What’s the science/reasoning behind it and are there  any other pre-harvest tips/tricks I should incorporate like not watering, lowering temps, etc.?


9 responses to “Dark Period Before Harvest”

  1. highhog_og


  2. highhog_og Avatar

    Good question

    1. Annette Furscroggen Avatar
      Annette Furscroggen

      Darkness before harvest is not exactly bro-science but there’s not a lot of data on it.

      These are my findings:
      1) Terpenes, resin and other secondary metabolites that form mainly during the dark cycle are at their highest levels at the end of it.
      2) Sugars travel to the root zone during the dark cycle to feed microbes resulting in smoother smoke.
      3) In any case, water just before chop to extend drying time (14 days is lagom).

      My practice has been to harvest after 48 hours.
      “It (THC) reaches the peak at the end of the dark period (night), and then cannabinoids get partly degraded by light during the day.”

  3. growingpain5 Avatar

    Some of the theories I’ve read include:

    1) Darkness increases resin production
    2) Darkness increases terpene production
    3) Terpene levels are at their highest at the end of the dark cycle right before lights on
    4) Sugars/starches recede from the plant to the root zone while in dark cycle resulting in a better tasting/burning bud
    5) Chlorophyll isn’t produced/active in the dark and existing chlorophyll begins to break down

    Other practices:
    1) keep them watered before chop to extend drying time (this makes sense)
    2) let them get bone dry to to increase resin/terpene production

  4. jmystro Avatar

    The best reason for extending the dark peroid for a few days would be to save on power. growingpain5 brings up some valid points he’s read based on the plant’s biology. I’ll go over them.

    1) Darkness increases resin production.

    During a plant’s dark cycle, respiration is in full swing. The light during the day provides the sugars/energy during respiration in the dark for growth of many things including trichomes and the oils inside. This is a normal process during flowering. When a plant is maturing and pretty much done, you shouldn’t see many, if any, clear trichomes forming. This is easy to check and don’t hold your breath waiting for more trichomes to form when the plant is finishing in those 3 dark days.

    2) Darkness increases terpene production.

    Terpenes and other secondary metabolites form mainly during the dark cycle.

    3) Terpene levels are at their highest at the end of the dark cycle right before lights on.

    Heat from the day evap’s volitle terp’s off we can smell so it make’s sense the highest levels would be when they are forming during the cycle with the coolest temps.

    4) Sugars/starches recede from the plant to the root zone while in dark cycle resulting in a better tasting/burning bud.

    This is also a normal cycle when the plant is growing leaf and photosynthesizing. At the end of the plants life there shouldn’t be much of anything going on if the plant is truly finishing. It’s a good practice for sure to cut during the dark cycle to gaurantee she hasn’t sucked anything up during a day time chop.

    5) Chlorophyll isn’t produced/active in the dark and existing chlorophyll begins to break down.

    This happenes during the drying period anyways.

  5. Herbncowboy Avatar

    Great post and replies.

  6. growingpain5 Avatar

    Thanks for the great info @jmystro, incredibly helpful. Is there a minimum/maximum time for the extended dark cycle to achieve these desired results? i.e. Is 24/36/48 hours not enough? Will going over 3 days of dark cause any undesired outcomes?

  7. jmystro Avatar

    You will not see any real benefit keeping your plants in the dark for the last 3 days. They go in the dark when you chop them. Plants have an internal clock that can be reset by being in the dark that long. You’d be fucking with her hormones that can do strange things like throw nanners with more than 3 days of darkness.

  8. SOUP Avatar

    I’ve seen no real science to explain the 3 day dark period thing. I’ve always considered it bro-science and don’t do it myself. Really seems like one of those broscience tips you get from the bro at the hydro store tryin to sell you somma dem bloom boostaas! (BRO GET DIS 0-50-30! Don’t you want your buds to get BOOSTED?!?!)

    I always try to harvest at the end of the dark period because thats when the odor is the strongest. (you can easily confirm this one for yourself with a sniff test). As mystro said, some terps evaporate off during the day, so chop them in the dark when levels are at their highest.

    Totally not convinced theres any benefit to the 3 days of darkness tho… Putting your plants in the dark for three days before harvest might actually lead to less flavor. While darkness helps preserve terpenes, photosynthesis helps create them. Some terps evaporate off each day, but many of the lost terps are replaced as long as the plant is still metabolizing. Chopping them in the dark seems like it could help preserve the existing terps, but keeping them in the dark for an extended period seems like it might interfere with the plant’s ability to make new ones to take their place. Over a three day dark period I suspect you’d end up with a net loss.

    I also like to keep watering my plants as usual up until the day of harvest. In my opinion one of the biggest things people can do to improve their flavor is SLOW DOWN THEIR DRYING, and keeping your plant well hydrated up until harvest day helps with that.

    This is especially true for you Colorado folks! No offense, but your beautiful state is crazy dry! I felt like a giant human shaped dried out sponge the whole time i was out there visiting. Gotta take every step you can to slow down your drying or you end up with that Colorado Crispy weed. 🙂

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