Cannabis terpenes are synthesized (manufactured) in the cytoplasm of the cells of the trichome head (TH) via the Mevalonic Acid pathway (MEV), and in plastids via the Methyl-Erythritol Phosphate pathway (MEP) . Monoterpenes, such as the pinenes (1), limonene, terpinolene and myrcene are a result of the MEV, while large terpenes like caryophyllene, farnesene and humulene are derived from the MEP. As the plant synthesizes more and more of the enzymes of terpene synthesis during flower, it makes perfect sense that their aroma becomes more prevalent and more precisely developed as the TH ripen.
Cannabinoids reach maximum concentration in the ninth week of flower (Aizpurua-Olaizola, et al, 2016). This is not a precise measurement, but rather a guide. Most growers believe harvest should take place whenever the TH become opaque and white, which is usually during the ninth week as molecules inside the TH pass their saturation point. Careful inspection and a watchful eye will notice the whiteness of TH without any need for magnification.
Simply keeping up with the number of flowering days elapsed will accurately hit this peak of cannabinoid concentration every time. There’s no need to break out the hand-held microscope and inspect flowers. Keep in mind that individual grow lights may be stronger or weaker than one’s flowers can tolerate, so results will vary. Nine weeks is sixty-three days. Cannabis plants should generally be harvested on day 63 of the flowering phase, when cannabinoid concentration is at or near its maximum to begin preserving the flower in this optimum composition.
Some plants require a longer flowering period, sometimes up to thirteen weeks, to mature (e.g. Laughing Buddha). Once a plant’s maturation period is established for your conditions, that number of days can be relied upon. It is written in the plant’s genetics and there is no escape. 🌂
Aizpurua-Olaizola, O., Soydaner, U., Öztürk, E., Schibano, D., Simsir, Y., Navarro, P., ... & Usobiaga, A. (2016). Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of natural products, 79(2), 324-331.
1. For the sake of brevity and to avoid confusion, terpenes are here named without prefixes such as "alpha" and "beta", as well as without chirality indications such the "d" prefix of d-Limonene.