How a Trichome Works: What That Frost on Your Plant Really Is

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That frost on your flowers isn't frost. Look closely at a ripening cannabis flower and it glitters: every sparkle is a tiny gland on a stalk, about as wide as a hair. Those glands are where the resin is made and stored, and they change as the flower matures. Here is how they work, what the famous colour chart really tells you, and why you should keep your hands off.

The short answer ▶ 0:30

A trichome is a hair on the plant's skin, and the resin-making kind is a gland. A ring of cells in its head makes the resin and pushes it into a sealed store above them. As the flower matures, that store changes colour.

Hairs and the three kinds of gland ▶ 0:46

Not every hair on the plant makes resin. Most of the hairs on top of the leaves are plain, pointed ones, and many carry a tiny grain of calcium carbonate, the mineral in chalk. They make nothing. The resin comes from the glands.

Source · Dayanandan & Kaufman, Am. J. Bot. (1976)

There are three kinds of gland. Bulbous: the smallest, scattered over the plant. Sessile: a round head sitting flat on the surface, common on leaves. And stalked: a bigger head raised on a stalk, crowded onto the flowers. The stalked ones make most of the resin.

Source · Tanney et al., Front. Plant Sci. (2021)

They are not fixed types. In a 2020 study of hemp flowers, Canadian researchers found that as heads gained more working cells, they tended to rise up on a stalk. So many of the stalked glands on a flower start life as sessile ones, and grow up. A sessile gland on a leaf has exactly 8 working cells in its head; a mature stalked gland on a flower has 12 to 16.

Source · Livingston et al., Plant J. (2020)

Inside the gland ▶ 1:41

At the base of the head sits a ring of disc cells: the factory floor. They make the resin's ingredients and push them upwards, into a space between their own walls and a thin, waxy skin called the cuticle. That space swells into the round head you see. It is a store, sealed off from the living cells below.

Source · Tanney et al., Front. Plant Sci. (2021)

Here is the clever part. In 2005, Japanese researchers found that the enzyme that makes THCA, the plant's main cannabinoid acid, is itself pushed out into that store. So the final step of the chemistry happens outside the living cells.

Source · Sirikantaramas et al., Plant Cell Physiol. (2005)

Why go to all that trouble? Because compounds like THCA can be toxic to the plant's own cells. Keeping them in a sealed store outside the cells protects the plant from its own chemistry.

And it isn't just cannabinoids. More than 120 terpenes, the smell compounds, have been found in cannabis, and the glands are where most of the flower's terpenes are made.

Source · Tanney et al., Front. Plant Sci. (2021)

What the resin is for (and UV-B) ▶ 2:41

So what is all that resin for? The best-supported answer is defence. Some of its terpenes repel insects, and the sticky resin can trap small ones. Scientists also suspect the glands help shield the flowers from ultraviolet light, but that is much less certain.

That suspicion is why some growers add UV lamps, hoping for more resin. But when Canadian researchers tested extra UV-B through flowering, it didn't increase the yield or what the glands produced, and terpene content actually went down. Their verdict: no commercially relevant benefit.

Source · Rodriguez-Morrison et al., Front. Plant Sci. (2021)

Clear, cloudy, amber ▶ 3:13

Under a magnifier, gland heads start clear, turn cloudy, then amber, and growers use this to judge when a plant is mature. What does the science say? In a 2022 study, Canadian researchers trained a computer to sort gland heads in close-up photos, week by week, across four varieties.

Clear heads peaked around day 25 of flowering. Cloudy heads peaked between day 50 and day 70, depending on the variety. Amber was absent until about day 50, then climbed fast near the end.

And the amber heads were smaller. In two of the varieties, cloudy heads were about 108 micrometres across, and amber ones about 90. So amber isn't a gland ripening further. It is a sign the gland is past its peak.

Source · Sutton, Punja & Hamarneh, Smart Agric. Technol. (2022)

Two honest caveats. That study didn't measure the chemistry inside the glands, and the three colours are a grower tradition, not categories science has tested. So treat the colours as a sign of the flower's age, not a precise recipe.

One more finding worth knowing. In a small test in the same study, flowers sprayed with a potassium bicarbonate mildew spray in weeks 5 and 6 had more amber glands and fewer cloudy ones a week later.

In your tent ▶ 4:30

First, those heads sit on very thin stalks, and they snap off easily. That sticky film on your fingers and scissors is broken glands. So handle flowers as little as you can.

Second, flowers in the upper canopy make significantly more cannabinoids and terpenes than lower ones, so the top and the bottom of one plant can look quite different.

Source · Tanney et al., Front. Plant Sci. (2021)

So: use a jeweller's loupe or a small lens, and look at the bracts, the little leaf-like parts of the flower, where most stalked glands sit. Check several buds, top and lower. Handle the plant as little as you can. And avoid spraying the flowers late in flowering.

The glitter is a crop of tiny sealed factories. Look with a lens, touch as little as you can, and read amber as age, not as a bonus. Next, the space those plants need: what size grow tent you actually need.