Ask growers where a crop is most easily ruined and many will not say pests or feeding. They will say the fortnight after the harvest. Months of careful work end on a string line or a drying rack, and the questions come thick and fast. How cold? How humid? How long? When does it go into jars, and how often should the jars be opened? Does waiting for amber trichomes really make the result more sedating?

Grower practice has confident answers to all of these. The research behind them is much thinner, and this article says so from the start. On post-harvest handling, CannaTinker's library of research papers holds one small drying experiment, one descriptive study that is available to us only as a preprint, and two broad reviews. A plant-architecture study and a European quality guideline add useful context. That is enough to explain what happens inside a drying bud, and to test one or two habits. It is not enough to confirm or overturn most of the curing routine. Where the collection is silent, we say so.

As with everything on CannaTinker, this is educational. In the UK, growing cannabis, even with a prescription, requires a Home Office licence (Home Office, 2024).

What practice recommends

The grow guide in the CannaTinker app, built from UK small-grow practice, sets out a routine that will be familiar to many home growers:

  • Harvest in the morning, before the lights come on, on the reasoning that terpene levels are highest then.
  • Dry at "60/60": 60 °F (about 16 °C) and 60% relative humidity, in darkness, for 10–14 days, with gentle air exchange and no fan blowing directly on the buds.
  • Check with the snap test: when a small stem snaps rather than bends, the buds are ready for jars.
  • Cure in glass jars with a 62% humidity pack and a small hygrometer, opening the jars daily for the first two weeks ("burping"), then weekly.
  • Judge ripeness by trichomes: clear, then milky ("peak THC"), then amber ("CBN, sedation"), aiming for roughly 75% milky and 25% amber.

This is practice: experience shared and refined by growers, not the result of controlled trials. That does not make it wrong. It does mean it deserves to be tested against what research can show.

What happens inside a bud after the cut

Three things change once a stem is cut: water leaves, cannabinoid acids slowly convert, and aroma compounds evaporate or transform.

Water

Fresh flowers are mostly water. Birenboim et al. (2024), summarising earlier work, put the weight lost in drying at up to 75%, over a typical drying period of two to three weeks. In their own experiment, fully dried buds had lost around 76–80% of their fresh weight, ending with a water content of about 10% (Birenboim et al., 2024). Drying is a race between two things: removing water quickly enough that moulds cannot take hold, and slowly or gently enough that the volatile compounds do not go with it.

Cannabinoid acids and decarboxylation

The living plant makes cannabinoids almost entirely in acid form: THCA rather than THC, CBDA rather than CBD. Turning an acid into its "neutral" form is called decarboxylation. The molecule loses a small group of atoms as carbon dioxide. Kim et al. (2024) describe the acid forms as converting under "light, heat, drying, combustion, or aging". Desaulniers Brousseau et al. (2021) note that this happens "during storage or heating" as non-enzymatic reactions, meaning ordinary chemistry rather than something the plant's enzymes drive. Sommano et al. (2020) add that it is "favored" by storage time. Even the Home Office's drug licensing factsheet records that THCA "readily degrades both naturally, and with a catalyst or environmental change (e.g. heat)" to THC (Home Office, 2024, para. 19).

Heat speeds this up dramatically. Kim et al. (2024), summarising earlier studies, note that accelerated decarboxylation starts above 90 °C. One research team proposed 150 °C as the optimum for converting THCA to THC. Drying temperatures are nowhere near that, so during drying the conversion is slow and partial. It still happens, as the studies below show.

THCA has a second possible fate. Desaulniers Brousseau et al. (2021) note that it "can be converted to" delta-8-THC, CBN (cannabinol) and CBNA. CBN is the compound grower folklore links to amber trichomes, and we return to it below.

Terpenes

Terpenes are the small, fragrant molecules that give each cultivar its smell: myrcene's "musky or hop-like" note, limonene's citrus, β-caryophyllene's pepper (Sommano et al., 2020). They come in two broad sizes. Monoterpenes are smaller and more volatile; sesquiterpenes are larger and evaporate less readily. Birenboim et al. (2024) found that monoterpenes "were more sensitive to the drying process than sesquiterpenes", which they explain by their higher volatility. The terpene profile is not fixed even before harvest. Sommano et al. (2020) note that it varies with variety, plant part, environment, maturity and analytical method. Desaulniers Brousseau et al. (2021) report that as flowers mature, monoterpenes accumulate relative to sesquiterpenes.

The drying experiment: Birenboim et al. (2024)

This is the one controlled drying study in the collection, and the details matter.

What was tested. The researchers, at Israel's Agricultural Research Organization, dried fresh flowers of two commercially grown medical chemovars from an Israeli farm. One was '240', a high-THCA type (THCA 9.5% of dry weight at harvest). The other was 'Gen12', a hybrid with substantial THCA (4.5%) and CBDA (10.0%). The paper gives no detail about how the plants were grown. The samples were small: plates of three buds weighing 2–4 g each, with five analytical replicates per treatment.

The two approaches. Most of the study tested laboratory controlled-atmosphere chambers at 15 °C. Dry gases and silica gel held the humidity below 10%, under three gas mixtures: normal air, nearly pure nitrogen, or a low-oxygen mix. As a reference, the team used what they called traditional drying: buds in breathable trays in a ventilated room at 15 °C and 50–55% relative humidity for 14 days, followed by one day with silica gel. The authors say this reference "imitated the commonly applied slow industrial drying procedure". For a home grower, it is also the closest thing in the collection to 60/60: slightly cooler and a little drier.

What they measured. Weight loss, mould (by counting colonies and by a DNA-based test), cannabinoids by liquid chromatography and terpenes by gas chromatography. Taste and smell were not assessed.

Drying time and mould

The chamber-dried buds stopped losing weight after six days. The open-air buds had not reached a stable dry weight after 14 days: the high-THC '240' buds had lost about 60% of their weight, against about 78% in the chambers. They needed the extra day on silica gel to finish.

Then came the mould. By day 12, about 80% of the open-air '240' buds were "highly infested" with Alternaria alternata, and some carried Botrytis cinerea, the grey mould that growers know as bud rot. Their Alternaria levels were one to two orders of magnitude higher than in fresh or chamber-dried samples. The authors attribute this to the longer time the buds spent with enough water available for mould to grow. In the hybrid 'Gen12', both moulds stayed below the detection limit before and after drying, whichever method was used.

So in one cultivar, conditions close to the home grower's favourite rule led to heavy mould. In the other, nothing happened. The authors' conclusion is that drying needs to be tailored to each chemovar.

Cannabinoids

In '240', THCA fell from 9.5% to 7.6% of dry weight under open-air drying. Under nitrogen or normal air in the chambers, the change was not statistically significant. THC rose about 3.5-fold in the open-air buds, from 0.07% to 0.24%. That rise was an order of magnitude smaller than the THCA lost, so most of the missing THCA did not become THC. The authors point to the longer drying time, the dry gases and silica gel used in the chambers, and the heavy mould as possible explanations. CBGA, the precursor from which the plant builds THCA and CBDA, fell by 42% under open-air drying.

In 'Gen12', THCA and CBDA held steady under every method, changing by less than 10%. Under open-air drying, THC and CBD still rose roughly eight-fold and three-fold respectively, without a matching fall in the acids. The authors conclude that formation and breakdown of cannabinoids "continue to occur during the drying process".

One finding matters for the amber debate. In both chemovars, the authors observed no increase in "isomerization or oxidation degradation products such as ∆8-THC or CBN" during drying (Birenboim et al., 2024).

Terpenes

Myrcene was the most fragile major terpene. It lost about 3–20% in '240' and 16–30% in 'Gen12' under most methods. Only the low-oxygen chamber mix preserved it, and in 'Gen12' it even rose by 15%. Limonene in 'Gen12' fell by 15–58%, depending on the method. Sesquiterpenes moved the other way. In '240', all methods raised them by 20–50%, and total terpene content rose by about 25–30%. In 'Gen12', total sesquiterpenes rose by 15–23%.

A rise in terpenes after drying sounds strange, but the authors suggest that "biological activities continue to occur" inside the flowers during drying. They attribute the changes to "degradation, evaporation, and oxidation". The practical lesson is that drying does not simply preserve or destroy aroma. It reshapes it, and differently in each cultivar.

What the authors found in earlier work

Birenboim et al. also summarise other drying studies, which we have not read in full. Hot-air drying cut drying time sharply but could reduce terpene levels by 80–90%, "particularly at higher temperatures". Infrared or microwave drying cut total volatile content by about 75%, mostly through loss of monoterpenes. They also cite earlier observations that drying on trays, compared with hanging, carries drawbacks such as greater mould susceptibility. They note too that the commonly used drying temperature range is 15–21 °C, and that industrial drying is "often more art than science".

Limits for a home grower

This is a careful study, but its conditions differ from a tent in important ways. The buds were tiny, 2–4 g, and lay on trays rather than hanging on branches. Only two chemovars were tested, from one commercial farm. The open-air reference was a single run at 15 °C and 50–55% relative humidity. No jar curing followed, apart from the one day on silica gel.

The preprint: Kim et al. (2024)

The second study asks a narrower question: how much decarboxylation happens during ordinary air-drying? An important caveat first. The file in our collection is the Research Square preprint, posted on 1 April 2024. The paper was later published in Scientific Reports, and we have not compared the two versions.

What was tested. The researchers, at Colorado State University Pueblo, grew a high-CBD hemp cultivar, 'Cherry Wine' (7.68% total CBD, 0.25% total THC), in a greenhouse. Plants had eight weeks of vegetative growth under 18-hour days, then flowered under 12-hour days, at 25 °C by day and 21 °C by night, with 70% humidity. Flowers were harvested in the eighth week of flowering and air-dried for 15 days at room temperature without sunlight.

The comparison. For fresh material, the team used a fine glass capillary under a microscope to draw resin directly out of the heads of the large stalked trichomes, 40 glands per sample. They compared this with an extract of the dried, ground flowers.

What they found. In the fresh trichome contents, CBD to CBDA was about 1:95 by weight. In the dried flowers it was about 1:20. That is roughly a four- to five-fold rise in the share of CBD. The authors conclude that "just an air-drying procedure without lighting or heating can induce a chemical transformation reaction". In other words, decarboxylation begins in the drying room, not only in a flame or an oven.

Limits. The two samples are different kinds of material: pure gland contents versus whole dried flower. So this is not a strict before-and-after measurement of the same tissue. Some of the paper's percentage summaries are also hard to reconcile with its tables, which is why we quote only the CBD-to-CBDA ratio. There is one cultivar, one drying condition and one time point. Terpenes and mould were not measured.

What the reviews add

The two reviews mainly provide context. Sommano et al. (2020) survey cannabis terpenes, their chemistry and aromas, and how they vary. Desaulniers Brousseau et al. (2021) focus on how light shapes cannabinoids and terpenes during growth. Their most useful contribution to this topic is an admission. "A nascent legal industry with proprietary value," they write, "slows access to reliable information on indoor cannabis production, postharvest practices and processing". The thinness of our collection here is not just bad luck. Much post-harvest knowledge sits with companies and has never been published.

Where the plant matters: a note on uniformity

One more study helps put the harvest in perspective, though it is not about drying. Danziger and Bernstein (2021) grew a high-CBD medical cultivar, 'Topaz', in a commercial Israeli greenhouse at about one plant per square metre, to roughly 2.5 m tall. They harvested 58 days after the switch to short days, "at the maturation stage accepted for commercial harvesting", and dried the flowers at 24 °C and 55% humidity for 14 days in a controlled chamber.

Flowers from the shaded bottom of the plant had cannabinoid concentrations up to 40% lower than flowers higher up. The large top flower was not always the strongest. The plants in a 1×1 tent are far shorter, so gradients are likely to be smaller. Still, the point carries over: what a jar contains depends on which buds went into it. A trichome check on a single top bud describes that bud, not the whole plant.

Slow versus fast drying

Put together, the evidence complicates the simple rule that slower is always better.

  • Too slow risks mould. In Birenboim et al. (2024), cool open-air drying left small buds damp for two weeks. One of two chemovars became heavily mouldy and lost THCA.
  • Too hot or too aggressive strips aroma. The hot-air, infrared and microwave studies that Birenboim et al. summarise lost large shares of terpenes, especially monoterpenes.
  • Fast and cool, in a controlled atmosphere, did best in that study: dry in six days with no visible mould and total terpenes preserved. But this used laboratory chambers with very dry gas and silica gel, not something a tent can reproduce.

The European GACP guideline for medicinal plants makes the same trade-off in general terms. Drying conditions must suit "the nature of its active constituent, such as essential oils". For open-air drying, material should be spread "in a thin layer" so that "uniform drying" avoids "mould formation" (EMA/HMPC, 2006, sections 12.3–12.4). It also recommends harvesting away from dew, rain or "exceptionally high air humidity" (section 11.3).

Practice the collection does not test

Several parts of the routine are neither supported nor contradicted by the collection. They have simply not been studied in the papers we hold.

60/60. No study tested it. The closest condition, 15 °C at 50–55% humidity, was too slow for small buds on trays and allowed mould in one cultivar. Hanging whole branches in a tent with air exchange is a different situation, so this is a warning sign rather than a verdict.

Jars at 62% and burping. Birenboim et al. (2024) describe industry curing as sealing flowers in containers and airing them periodically to remove leftover moisture, a process that can take two to three weeks. They do not test it, and no source measures what a 62% pack does to cannabinoids, terpenes or taste.

Morning harvest. The idea that terpenes peak before lights-on is not tested anywhere in the collection. The only related advice is GACP's general caution against harvesting in wet or very humid conditions.

"Amber = CBN = sedation". The chemistry that THCA can become CBN is real (Desaulniers Brousseau et al., 2021). But no source in the collection links trichome colour to CBN content, and none measures sedation. In the one drying study that looked, CBN did not increase during drying (Birenboim et al., 2024). The amber rule stands as practice.

Flavour "opening up" in the jar. No source measured taste or smell as people perceive them. The studies measured concentrations of compounds.

What this means for a 1×1 tent

These takeaways are educational and deliberately moderate. The evidence base is thin.

  • Cool and dark fits the evidence. The commonly cited drying range is 15–21 °C. Light, heat and storage time all push decarboxylation along. Gentle drying conditions protect monoterpenes; heat strips them.
  • Watch the speed, not just the numbers. If buds still feel damp and stems bend after the expected time, drying is too slow. A musty smell or grey fuzz means mould has started. Mouldy material is best discarded, not cured. Lowering humidity slightly and improving air exchange, without blowing directly on the buds, is the usual practice response.
  • Give buds space. Dense clusters dry unevenly. GACP's "thin layer" and "uniform drying" principle applies as much to a hanging line as to a rack.
  • Jar only when the outside is dry. A jar traps whatever water is left. A small hygrometer that climbs quickly after sealing is a sign the buds need more time.
  • Store cool and dark. Conversion continues slowly in storage.
  • Treat the rest as practice. Morning harvests, 62% packs, burping schedules and amber targets are reasonable habits from experience. The collection neither confirms nor refutes them.

What we know, and what we don't

What we know, with low confidence. Drying removes about three-quarters of a flower's weight. Cannabinoid acids begin converting to their neutral forms during ordinary air-drying, even without heat or light (Kim et al., 2024). Slow, cool open-air drying of small buds left them damp for two weeks, and in one of two chemovars led to heavy mould and THCA loss (Birenboim et al., 2024). Monoterpenes such as myrcene and limonene are the most fragile aroma compounds, while sesquiterpenes may rise during drying. Chemovars respond differently to the same drying conditions.

What we don't know. No source in the collection tests 60/60, jar curing, humidity packs, burping, morning harvests or trichome-colour targets. None measures taste or smell as perceived. None tests whole branches hanging in a home tent. The drying study used tiny buds of two Israeli medical chemovars. The decarboxylation study used one hemp cultivar, and we read it only as a preprint. As Desaulniers Brousseau et al. (2021) note, much of what the industry knows about post-harvest handling has never been published. Until it is, the curing routine remains grower practice, plausible and worth respecting, but untested.

Sources

Birenboim, M., Brikenstein, N., Duanis-Assaf, D., Maurer, D., Chalupowicz, D., Kenigsbuch, D. and Shimshoni, J.A. (2024) 'In pursuit of optimal quality: cultivar-specific drying approaches for medicinal cannabis', Plants, 13(7), 1049. doi:10.3390/plants13071049.

Danziger, N. and Bernstein, N. (2021) 'Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants', Plants, 10(9), 1834. doi:10.3390/plants10091834.

Desaulniers Brousseau, V., Wu, B.-S., MacPherson, S., Morello, V. and Lefsrud, M. (2021) 'Cannabinoids and terpenes: how production of photo-protectants can be manipulated to enhance Cannabis sativa L. phytochemistry', Frontiers in Plant Science, 12, 620021. doi:10.3389/fpls.2021.620021.

EMA/HMPC (European Medicines Agency, Committee on Herbal Medicinal Products) (2006) Guideline on Good Agricultural and Collection Practice (GACP) for starting materials of herbal origin. EMEA/HMPC/246816/2005. London: EMEA.

Home Office (2024) Drug licensing factsheet: cannabis, CBD and other cannabinoids. Updated 3 October 2024. London: Home Office. Available at: https://www.gov.uk/government/publications/cannabis-cbd-and-other-cannabinoids-drug-licensing-factsheet/drug-licensing-factsheet-cannabis-cbd-and-other-cannabinoids.

Kim, E.-S., Park, S.-H., Kinney, C., Olejar, K.J. and Corredor-Perilla, C.I. (2024) 'Decarboxylation of acidic cannabinoids in Cannabis sativa during storage period'. Preprint, Research Square, posted 1 April 2024. doi:10.21203/rs.3.rs-4078895/v1. Published version: 'Comparison of decarboxylation rates of acidic cannabinoids between secretory cavity contents and air-dried inflorescence extracts in Cannabis sativa cv. "Cherry Wine"', Scientific Reports (2024). doi:10.1038/s41598-024-66420-3.

Sommano, S.R., Chittasupho, C., Ruksiriwanich, W. and Jantrawut, P. (2020) 'The cannabis terpenes', Molecules, 25(24), 5792. doi:10.3390/molecules25245792.