Tetrahyrdocannabinol or as its better known – THC – is the psychoactive cannabinoid in cannabis that gets you “high”. THC is found within trichome heads of a ripe cannabis flower. Trichomes are a protuberance off of the cannabis flower that contains a mushroom-shaped head where the THC along with other compounds are contained. To observe trichomes in their full glory – a person would need to use a jeweler's loop to be able to see them up-close, so let's dive in.
Within cannabis there are at least 113 cannabinoids identified. To develop an understanding of THC creation and how it pertains to cultivation specifically we need to comprehend its precursor compounds as well as how it degrades into other compounds. Firstly, cannabigerolic acid (CBGA) is the direct precursor to tetrahydrocannabinolic acid (THCA), cannabichromenic acid (CBCA), and cannabidiolic acid (CDBA). Once the plant begins to grow past peak-ripeness the THCA begins to degrade into cannabinol (CBN). To summarize, CBGA turns into THCA, CBCA, and CBDA. THCA naturally degrades into CBN as it is exposed to heat, light, and air. A person can determine peak ripeness of a cannabis plant by measuring THCA over time to determine when optimal harvest time is.
In addition to understanding THC on a chemical level, it is also vital to understand it from a visual perspective as well. To determine peak ripeness there are several factors to consider. Firstly, most of the senesced stigmas (white or brown “hair” like protuberances) should have turned brown from white. Secondly, the aroma of the flowers will be most pungent. Next, the buds should be firm. Lastly, the trichomes heads should appear milky white and just starting to turn amber. When the trichome heads are clear the CBGA has not yet began to synthesize into THCA.When the trichome heads are cloudy the CBGA has synthesized into THCA. Lastly, when the trichome heads begin to go amber the THCA is degrading into CBN.
It's particularly important to consider the intent of why you are growing when deciding on harvest time because CBGA, THCA, and CBN when combusted and consumed have different effects on the consumer. For example, CBGA is classified as non-psychoactive but it is reported to have therapeutic qualities. THC on the other hand is psychoactive and will lead to you feeling “high”. Lastly, CBN is a highly sedating compound that can leave one couch-locked and ready for bed. In a personal grow, it can be fun to experiment with different harvest-times and the resulting effects. In the recreational market – the focus tends to be THC. As you can see, determining peak ripeness and harvest time plays a major role in THC levels and the user experience.