What trichomes are
The word trichome comes from the Greek for hair (Wikipedia), and many plants have them. On cannabis, the important ones are glandular trichomes: tiny stalks topped with a round head, packed onto the female flowers. Cells at the base of each head make cannabinoids and terpenes, which collect in a storage space under the head's outer skin (Tanney et al., 2021). Those terpenes give each strain its smell, as the complete guide to cannabis terpenes explains.
The frosty coat on well-grown flower is a dense layer of these glands. A University of British Columbia study confirmed that the largest, mushroom-shaped stalked trichomes are the richest source of the compounds that form THC and CBD, and of fragrant terpenes (UBC Science).
The glands mostly hold THCA rather than THC. THCA converts to THC with heat, and some converts slowly after harvest during processing and storage (Tanney et al.).
The 3 types of glandular trichomes
Scientists first sorted cannabis glandular trichomes into 3 types in 1973, using electron microscopes (Tanney et al.):
- Bulbous: the smallest, on a short base about 10 to 15 micrometres tall, with a head 15 to 30 micrometres across (Punja et al., 2023).
- Capitate-sessile: a round head on a very short stalk. True sessile trichomes, found on leaves, have exactly 8 secretory cells, and many sessile-looking glands on young flowers turn out to be an early stage of stalked ones (Tanney et al.).
- Capitate-stalked: the largest, with 12 to 16 secretory cells and a head 40 to 110 micrometres across on a stalk anywhere from 20 to 1,100 micrometres long. These produce the most cannabinoids (Tanney et al.; Punja et al.).
Where trichomes grow and why
Under ultraviolet light, stalked trichomes glow blue and sessile ones red, and the UBC team suggested UV light could help monitor trichome maturity (UBC Science). Cannabis leaves and stems also carry non-glandular hairs that do not make resin (Punja et al.).
Stalked trichomes are concentrated on the calyces and bracts of female flowers and spread onto the small sugar leaves around the buds. Male plants make only small amounts of cannabinoids (Tanney et al.).
Why the plant makes them is not fully settled, but the evidence points to defence. Insect-repelling terpenes are concentrated in the flowers, THCA and CBGA killed insect cells in lab tests, and early research suggested THC may help protect against UV radiation (Tanney et al.).
How growers read trichome colour
As flowers mature, the resin in trichome heads changes from clear to cloudy, or milky white, and then to amber or brown (Punja et al.; Tanney et al.). Growers use that shift, along with the colour of the pistils, the hair-like strands on the buds, as a sign a plant is ready to harvest (Crispim Massuela et al., 2022; a 2025 harvest-timing study).
- Clear: translucent heads that have not yet matured.
- Cloudy or milky: the mature stage, before browning.
- Amber or brown: linked with the plant's senescence, or ageing. A crop harvested at this stage is often described as too late, with a potential loss of quality as THCA breaks down (Crispim Massuela et al.).
Why colour is only a rough guide
There is no agreed standard. Heads on the same bract mature at different times, and plants keep forming new flowers and trichomes late in the season, so readings depend on where you look. Researchers say unbiased, quantitative ways to judge harvest time from trichome colour are still missing (Crispim Massuela et al.; Punja et al.).
Individual heads are a fraction of a millimetre across, so checking them takes magnification. Researchers are building tools to take out the guesswork: a Simon Fraser University team trained a deep-learning model to sort trichome heads into clear, milky and brown from close-up photos taken across an 8-week flowering period (Simon Fraser University).
You may also read that cloudy heads give a more heady effect and amber a heavier one. Treat that as grower lore: researchers note that cannabis growing advice has largely been based on anecdote rather than scientific evidence (Tanney et al.). If you grow your own, the beginner growing guide covers the full cycle.
After harvest: handling, kief and hash
Trichome heads break off easily. In a 2023 study, machine-trimmed buds had many heads detached or collapsed, while hand-trimmed buds kept their heads intact, and drying also changed trichome structure (Punja et al.). The guide on how to dry and cure weed buds covers that step.
Loose trichomes are kief, the white, sticky dust that collects in a grinder's bottom chamber. Kief is the main ingredient in hash, which is made from loose trichomes or pressed resin (Health Canada; CAMH). Read what hash is and how it is made, or shop hash.
Buying frosty flower
Intact trichome heads are a sign buds were handled gently (Punja et al.), but THC and terpene levels come from lab testing. GasDank delivers same day across Toronto and the GTA, usually within 1 to 2 hours, and ships mail order across Canada. The menu carries lab-tested products; browse all flower. Customers must be 19 or older (21 in Quebec), with ID checked at the door.
