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What Are They
Trichomes are the small hairs or outgrowths from the epidermis of a plant that are seen on the buds, leaves, and stalks of cannabis. They are the reason for that brilliant carpet of glittering white that coats cannabis flowers. They produce terpenes and flavonoids (chemicals related to the smell and taste of the bud), and they produce cannabinoids (chemicals such as THC or CBD that bind to cannabinoid receptors in the body) as well as maintain their storage.
Trichomes have many important purposes including defense against insects and other herbivores, defense against pathogens, protection from UV light burn, and even foliar water absorption.
In dry atmospheric conditions, more trichomes will be produced to better absorb and retain water giving plants in areas of scarcity protection from dehydration. Higher amounts of UV-B light can increase trichome density as well to keep the plant surface from receiving too much high intensity radiation and to mitigate or prevent light burn. Trichomes can even act as feeding deterrents for herbivores through terpenes and alkaloids created within the trichomes secretory cells. Trichomes are complex as well as fascinating and come in several forms.
Types
There are two main categories of trichomes on cannabis and they are known as Glandular and Non-Glandular trichomes. Each category contains a few subtypes of trichomes:
Glandular Trichomes: Trichomes that possess a glandular head and secrete secondary metabolites such as cannabinoids, terpenes, and flavonoids.
–Capitate-Stalked Trichomes: Glandular trichomes that produce and store the highest amount of terpenes, flavonoids, and cannabinoids (all also known as secondary metabolites). They have spherical or ovoid heads atop slender, cylindrical stalks. They resemble tiny mushrooms and can be anywhere from 150-500 microns tall. These only form after cannabis has begun flowering.
–Capitate Sessile Trichomes: Glandular trichomes that produce and store secondary metabolites but at a lower concentration than capitate-stalked trichomes. They have spherical or ovoid heads and a unicellular stalk or no stalk. These appear to be ‘sitting’ just above plant surfaces instead of being raised up by a tall stalk. These trichomes are between 25-100 microns in size.
–Bulbous Trichomes: The smallest kind of glandular trichome at 15-30 microns in size, bulbous trichomes are tiny and globular with no stalk beneath them. They are found all over cannabis plants and produce very limited amounts of cannabinoids.
Non-Glandular Trichomes: Trichomes that provide physical defenses, do not have glandular heads, and do not produce or store secondary metabolites.
–Cystolithic Trichomes: Found on the upper and lower surfaces of leaves resembling tiny bear claws with a calcium deposit for a base. These trichomes are between 150-220 microns in height. These trichomes produce neither cannabinoids nor terpenes.
–Non-Cystolithic Trichomes: Very slender trichomes with no heads and no bear claw shape at their base. Often found on the lower side of leaves and on bracts of the cannabis flower as well as on stalks. They produce neither cannabinoids nor terpenes but act as physical barriers to disrupt pests and pathogens.
Visual Indicators of Harvest Readiness/Maturity
Trichomes change in appearance during the maturation of the cannabis plant. It’s this change in appearance that can act as a strong visual cue of harvest readiness.
Trichomes can be found on the leaves and stems of young plants but most trichomes start to appear during the flowering stage and are largely centered on the buds or flowers of cannabis. It’s common to see them grow on leaf surfaces as well as stalk surfaces and their presence on leaves can indicate that the cultivar will have high trichome production.
Trichomes begin with clear or transparent heads that become opaque or milky/cloudy with time. They will eventually turn to an amber or honey color if left to develop for long enough. These color differences indicate that chemical changes are occurring within the trichome’s head.
Clear trichome heads indicate the trichome is still young and filled more with CBGA, which is a precursor to THCA and CBDA (which are themselves the precursors to THC and CBD).
As the trichome matures it becomes milky or cloudy. This indicates the highest amount of THCA content. The cloudier the trichome head becomes without turning amber, the more THCA is present inside the trichome head.
If the flowering plant is grown long enough trichomes will change again from cloudy and opaque to an amber which indicates higher CBNA (precursor to CBN) and lower THCA levels than in its cloudy stage.
Many people like to harvest when more than half of their capitate-stalked trichome heads turn cloudy with little to no amber heads. Some people wait to harvest until as much as 70% of their trichome heads are cloudy with a few amber heads and the remaining ~30% still being clear. Others will prefer to harvest when there is a higher percentage of amber trichome heads as this will usually lend itself to more sedative effects from the flower due to higher CBNA content. There is much debate over the best ratios of cloudy to clear trichome heads for optimal harvest time, but regardless, the more opaque and cloudier the appearance of a trichome, without any amber, indicates the highest amount of THCA it will have.
It is not uncommon to see purples in the stalks and/or heads of capitate stalked trichomes. The color purple is a result of pigments called anthocyanins made within the plant. Normally anthocyanins are more commonly seen in the leaves and the bracts of the flowers of cannabis as well as on the stalks but occasionally it can make its way into trichomes. The presence of anthocyanins does not act as an indicator of increased or decreased potency but does look stunningly gorgeous.
Trichomes are incredible evolutionary adaptations that have complex interactions between plants and their environment as well as produce the substances that many people enjoy recreationally and medically. The multifaceted nature of trichomes and their contents allows them to aid plants in survival, interact with human biochemistry, and endure as one of nature’s true works of art.
