When to Harvest Cannabis Trichomes: Colour and Maturity Signs
Two features of the flower mainly indicate when to harvest cannabis trichomes and buds: the colour of the glandular trichome heads and the colour of the stigmas. As trichomes mature, their resin changes from clear to cloudy (milky) to amber and then brown. Stigmas shift from whitish-yellow to reddish-brown. Grow guides also list swollen, firm calyxes as a sign of ripeness. This article focuses on the maturity signs described in the studies below, that is, trichome and stigma colour as markers of cannabinoid development and plant ageing, rather than as predictors of a particular effect.
The colour stages occur side by side though, because trichomes form at different times. On a single bract, a 2023 Canadian study counted 83 clear, 96 cloudy and 52 brown trichome heads near the end of flowering.
Clear, cloudy and amber trichomes as a ripeness sign
Ripeness can be read from the stalked glandular trichomes. According to a botanical paper the Canadian study draws on, these sit most densely on the bracts around the calyx and on the small, simple leaflets within the flower cluster. How these glandular hairs are built is covered in What Are Trichomes. Where the calyx, bracts and stigmas sit on the flower is shown in The Structure of the Cannabis Plant.
As the glandular heads mature, their resin first turns cloudy, milky white, then amber to brown. The study in the Journal of Cannabis Research links this browning to the ageing of the heads: they fluoresce less under UV light, die off and detach. Among growers, the authors note, this colour change is considered a sign of over-mature flowers.
In this study, plants spent 2 weeks in the vegetative stage under an 18-hour light period, then 8 weeks under a 12-hour light period in a flowering room. Two genotypes were examined from week 3 to week 8 of flowering. From around week 5, the heads began secreting resin, ageing and dropping off. After 8 weeks, a high proportion were visibly brown. A colour measurement on a further variety showed decreasing translucency alongside increasing red content from week 3 through week 5 to week 7.
A second paper involving the same research group appeared in 2023 in the journal Smart Agricultural Technology. It used an automated method to classify the trichome heads of 4 varieties by colour between week 3 and week 9 of flowering. The authors noted that the relationship between trichome colour and flower development had not previously been studied, and interpret the colour-stage timelines as strain-independent indicators of flower development.
Colour stage | Appearance of the heads | Finding in a study with 4 varieties (2023) |
|---|---|---|
Clear | translucent | most common around day 25 of flowering |
Cloudy | cloudy, milky white | highest share between day 50 and day 70, depending on variety |
Amber to brown | amber to brown | rapid increase between day 65 and day 75 |
Why trichomes don't mature at the same time
The authors of the Journal of Cannabis Research study attribute the mixed colour stages to the staggered formation of the glandular heads. In both genotypes, trichome density rose gradually up to week 6.
The genotypes also differed: after 6 weeks, trichome stalks were around 500 µm long in one and around 300 µm in the other.
Differences also appeared within the flower. After 6 weeks, the underside of the bracts carried significantly more stalked glandular trichomes than the top side in both genotypes. Trichome density on the top side, by contrast, did not differ significantly between samples taken from the lower, middle and upper parts of the flower clusters.
Head shape also changes as maturation progresses. Secreted resin droplets caused many heads to stick together or collapse. After drying and mechanical trimming, the study found that many glandular heads had become detached or had collapsed.
Checking trichomes with a magnifier or microscope
For visual inspection, German-language grow guides recommend a magnifying glass or pocket microscope with 20 to 50x magnification, or at least 30x. In the Canadian study, bracts were cut with a razor blade from the top, middle and bottom of each flower cluster and examined under a stereomicroscope at 50x magnification. The paper in Smart Agricultural Technology relied on macro photography and on fluorescence triggered by UV light.
Human visual inspection is considered unreliable in research. A 2026 study in the journal Agriculture describes the usual assessment of trichomes and stigmas as subjective and therefore inconsistent. The researchers used simple smartphone-based systems to capture over 14,000 images in a greenhouse and a laboratory. A classification model assigned trichomes to the clear, cloudy and amber classes with an accuracy of 98.6%. A 2025 Australian study lists individual colour perception, experience from previous harvests, and simple user error as sources of error in manual assessment.
Stigma colour as a ripeness sign
Stigmas, botanically the pistils, are the organs of the female flower that receive pollen. According to the Australian study, growers have traditionally used their colour as an indicator of when a plant produces the most cannabinoids. In the Canadian study, stigmas shifted from whitish-yellow to reddish-brown as the plant matured. After harvest and drying, they took on a deep orange-brown tone.
The Australian study, published in 2025 in the journal Plants, tested this relationship. 25 genotypes were grown under a 16-hour light period and then flowered under a 12-hour light period. Over 119 days after the start of flowering, 4 flower clusters per genotype were harvested, assessed by image analysis and analysed with liquid chromatography and mass spectrometry. The researchers assigned stigma colour to 4 stages:
fully white
partly amber
mostly amber
fully amber
In 22 of the 25 genotypes, the highest total cannabinoid concentration occurred at stage 3 or 4, with 10 of these peaking at stage 3 and 12 at stage 4. One genotype reached its peak already at stage 1. For total cannabinoid yield, 18 genotypes peaked at stage 4 and 7 at stage 3. The authors consider the rule of thumb of harvesting when stigmas are mostly amber a useful approximation in most cases, but see a need for research on individual genotypes. Why stigma colour and cannabinoid production should be linked is, in their account, not scientifically established.
The study in Agriculture reached a similar conclusion. There, the stigma colour change from green to orange coincided with the highest cannabinoid concentration, measured by high-performance liquid chromatography.
Percentages cited in grow guides
Fixed shares of discoloured stigmas at which a plant is considered ready to harvest come from grow guides. The figures vary:
Source | Share of discoloured stigmas cited |
|---|---|
Daily newspaper, science section (2024) | at least 40%, harvest window 40 to 70% |
Cannabis trade magazine (2019) | 50 to 75% |
Gardening guide website | 70 to 90% |
Calyxes
A cannabis trade magazine and a gardening guide website cite swollen, firm calyxes as a further ripeness sign. The bracts around the calyx are also where most of the trichomes used for colour assessment are found.
Flowering time and cannabinoid levels over time
The number of weeks since the start of flowering only sets a rough frame. In the Canadian study, flower clusters were harvested after 7 to 8 weeks of flowering.
A field study on industrial hemp, published in 2020 in the Journal of Agricultural and Food Chemistry, examined 3 day-length-sensitive and 2 day-length-neutral varieties. Flowers were sampled weekly, starting 2 to 4 weeks after anthesis and continuing until the plants senesced. THC, CBD and CBG levels rose with maturity and reached their peak 6 to 7 weeks after anthesis. After a plateau stage of varying length depending on variety, levels declined again as the plants aged.
The Australian study points to earlier findings that the most suitable harvest time differs between genotypes and that THC and CBD reach their peaks at different times. A single timeframe that fits all genotypes is, in the authors' assessment, difficult to derive from this.
Harvesting home-grown cannabis in Germany: the KCanG
Rules for growing and harvesting cannabis at home differ by country; the following describes the law that applies in Germany. Under § 9(1) of the German Cannabis Act (KCanG), adults aged 18 and over may grow no more than 3 cannabis plants at a time at their residence or habitual place of stay. Under § 9(2) KCanG, whatever is harvested may not be passed on to third parties. Possession at the place of residence is governed by § 3(2) KCanG: up to 50 grams of cannabis and up to 3 living plants are permitted. For flower and other plant material, the weight counts after drying. The amounts permitted outside the home are summarised in Cannabis Possession in Germany: Permitted Amounts under the KCanG.
Frequently asked questions
How do you know when cannabis is ready to harvest?
The main ripeness signs are the colour of the trichome heads, which changes from clear through cloudy to amber and then brown, and the colour of the stigmas, which shift from whitish-yellow to reddish-brown. Grow guides also cite swollen, firm calyxes.
What's the difference between cloudy and amber trichomes for harvest timing?
They mark later stages of maturity. In a study with 4 varieties, the share of cloudy heads peaked, depending on variety, between day 50 and day 70 of flowering, while brown heads increased rapidly between day 65 and day 75. The browning coincides with the ageing of the glandular heads.
What magnification do you need to check cannabis trichomes?
German-language grow guides cite magnifying glasses or pocket microscopes with 20 to 50x magnification, or at least 30x. In a Canadian study, bracts were examined under a stereomicroscope at 50x magnification.
Why aren't all trichomes on a plant the same colour?
Trichomes form at different times, so heads of different maturity sit side by side on a single bract. One study counted 83 clear, 96 cloudy and 52 brown heads on a single bract.
What percentage of stigmas should be dark before harvest?
Grow guides cite differing shares, between 40% and 90% of discoloured stigmas. In a study with 25 genotypes, the highest cannabinoid concentration occurred in 22 genotypes at the stages with mostly or fully amber stigmas.
Sources
§ 9 KCanG – Anforderungen an den privaten Eigenanbau, Bundesministerium der Justiz
§ 3 KCanG – Erlaubter Besitz von Cannabis, Bundesministerium der Justiz
Der richtige Erntezeitpunkt für Cannabis, Hanf Magazin (Autor: Robert Meister)
Cannabis: Wann ernten?, Stuttgarter Zeitung (Autor: Michael Bosch)
As of: 22 October 2026
This article is for informational purposes only and is not a substitute for medical or therapeutic advice. If you have any health-related questions, please consult a doctor or another qualified professional.