Drying Cannabis: Process, Climate and Duration
Drying cannabis means removing water from freshly harvested flower until it is stable enough for storage. For the common slow-drying method, a review article in the journal Bioengineering (2022) and a factsheet from Oregon State University list 18 to 21 °C at 50 to 55 % relative humidity in a dark, ventilated room. Depending on the source, the process takes 5 to 6 days or 2 to 3 weeks.
Most of the published figures come from research on industrial hemp and medical cannabis. According to these studies, climate and method affect microbial load as well as the content of terpenes and cannabinoids.
Why fresh cannabis flower is dried
Freshly harvested flower consists of roughly 78 to 80 % water, according to the Bioengineering review. In a study by Israeli research institutions covering 2 chemovars (journal Plants, 2024), the flower lost 77.4 % and 78.5 % of its weight during a 6-day drying period in a controlled atmosphere. According to the review, insufficient control of drying and storage leads to mold.
In Germany, drying is also the reference point for legal possession limits. Under the German Cannabis Act (KCanG), Section 3(1) and (2) set allowed possession limits for flower, flower-adjacent leaves and other plant material based on the weight after drying. Adults may possess up to 25 grams for personal use, up to 50 grams at their place of residence or habitual abode, and no more than 50 grams in total. Private home cultivation is limited under Section 9(1) KCanG to 3 plants at a time, and cannabis from home cultivation may not be passed on to third parties under Section 9(2) KCanG. Rules on cannabis possession and cultivation differ from country to country, and the figures above apply only within Germany.
From trimming to hanging the buds
Leaves are removed from the flower clusters either before or after drying. The review distinguishes wet trimming before drying from dry trimming after drying or curing. In both cases, the authors note, the goal is to preserve the structure of the trichomes.
In classic hang-drying, stems hang with the flower clusters pointing downward on wires in a room with stable temperature until the targeted water activity is reached. Alternatively, flower is laid out on racks or trays. For rack drying, the review lists around 4 to 5 days, and for slow drying under close-to-ambient conditions, 5 to 6 days.
The 2022 Oregon State University factsheet on industrial hemp flower describes slow drying in a dark, well-ventilated space such as a barn or shipping container, with climate controlled using fans, dehumidifiers or heaters.
Temperature and humidity during drying
Both the factsheet and the review agree on 18 to 21 °C and 50 to 55 % relative humidity for slow drying. In the control groups of more recent studies, conventional drying ran somewhat cooler or warmer.
Study | Material | Temperature | Humidity | Duration |
|---|---|---|---|---|
Israeli study, Plants (2024) | medical cannabis, 2 chemovars | 15 °C | 50 to 55 % | 14 days plus 1 day curing |
Microwave-drying study, Cannabis and Cannabinoid Research (2024) | medical cannabis, THC-rich chemovar | 16 °C | 50 % | 10 days |
Cornell University study, Plants (2025) | industrial hemp, 2 cultivars | 25 °C | 45 % | 1 week |
Higher temperatures change the material. The review cites a study on hemp in which raising the drying temperature from ambient to 90 °C reduced the share of terpenes retained from 82.1 % to 29.9 %, while decarboxylation of CBDA rose from 0.2 % to 14.1 %.
How long cannabis takes to dry
There is no single accepted duration. The Bioengineering review lists 5 to 6 days for slow drying. In their introduction, the authors of the Israeli study describe a drying phase of 2 to 3 weeks that depends, among other things, on temperature and humidity. In the experiments themselves, conventional drying ran at 15 °C, 16 °C and 25 °C, lasting between 1 week and 14 days.
How dryness is measured
One benchmark for completed drying is water activity (aw). The 2022 revision of ASTM D8197 sets a range of 0.55 to 0.65 for dried cannabis flower. The upper figure is meant to prevent the growth of microorganisms such as mold, the lower figure to prevent damage from breakage during handling and storage. If water activity exceeds 0.68, the standard calls for further drying. As residual moisture after 10 days of conventional drying at 16 °C, the microwave-drying study measured 13.10 %.
Mold and terpene loss during drying
According to the authors of the Israeli study, long drying periods raise the risk of mold because moisture escapes only slowly. By day 12 of their experiment, around 80 % of the conventionally dried flower from the chemovar labeled 240 was heavily affected by the fungus Alternaria alternata, with a smaller degree of Botrytis cinerea. In the microwave-drying study, microbial load under conventional drying rose by 2 log units. In the Cornell University study, the samples dried in ambient air showed the highest yeast and mold counts.
Drying also causes loss of volatile terpenes. A 2020 paper in the Journal of Cannabis Research cites a 1996 study in which air-dried and subsequently stored flower lost 31.0 % of its terpene content after 1 week, 44.8 % after 1 month and 55.2 % after 3 months, compared with fresh material.
Faster drying methods in research
The Israeli study dried flower at 15 °C in chambers with controlled gas composition, including pure nitrogen and a mix of 5 % carbon dioxide, 5 % oxygen and 90 % nitrogen, at a humidity below 10 %. Drying and curing time fell by at least 60 % compared with the conventional method, while volatile terpenes were preserved. Under nitrogen, the THCA content of the THC-rich chemovar did not differ significantly from the level measured at harvest. The authors conclude that each chemovar may require its own drying conditions.
In the microwave-drying study, flower from a THC-rich chemovar was dried at 40, 50, 60 and 80 °C and analyzed for 67 cannabinoids and 36 terpenoids. At 50 °C, drying time fell from 10 days to well under a day, with THC content similar to conventional drying. At 80 °C, THC concentration rose markedly, while terpenoid content fell by about 50 %.
The Cornell University study on 2 industrial hemp cultivars compared hot air at 75 °C for 8 hours, ambient air at 25 °C and 45 % humidity for 1 week, and freeze-drying for 24 hours. Total cannabinoid content did not differ significantly between methods. With hot air, however, decarboxylation reached 8.5 to 9.0 %, compared with under 0.1 % for the other two methods, and yeast and mold load was around 2 log units lower.
According to the Oregon State University factsheet, convection, infrared and freeze-drying are also options, though they require substantial investment.
Curing and storage after drying
Drying is usually followed by curing: the flower continues to mature in sealed containers that are opened at intervals. The Oregon State University factsheet lists 14 days at 18 °C and 60 % relative humidity, at a water activity below 0.65. A study cited in the review rated 18 °C and 60 % over 2 weeks, with the lid opened after 6 hours, as the best condition. In the Cornell University study, curing lasted 3 weeks at around 25 °C in the dark, in glass jars or foil bags.
For storage, the factsheet lists 18 °C and 45 to 55 % relative humidity; light, air and high temperatures are said to reduce cannabinoid content. According to the review, storage at 22 °C under light exposure is strongly detrimental to cannabinoids compared with dark storage at 4 °C.
Frequently asked questions
At what temperature and humidity is cannabis dried?
For slow drying, a factsheet from Oregon State University and a review in Bioengineering (2022) list 18 to 21 °C and 50 to 55 % relative humidity. In studies, conventional drying also ran at 15 °C, 16 °C or 25 °C.
How long does it take to dry cannabis?
The Bioengineering review lists 5 to 6 days for slow drying and around 4 to 5 days on racks. Other researchers describe a phase of 2 to 3 weeks; in studies, conventional drying lasted between 1 week and 14 days.
How is it measured whether buds are dry enough?
One benchmark is water activity. The ASTM D8197 standard sets a range of 0.55 to 0.65 for dried cannabis flower and calls for further drying above 0.68.
How much weight do cannabis buds lose while drying?
Fresh flower consists of roughly 78 to 80 % water, according to a review article. In a study with 2 chemovars, flower lost 77.4 % and 78.5 % of its weight during drying.
Under German law, does cannabis possession count fresh or dried weight?
Under Section 3(1) and (2) KCanG, German possession limits for flower, flower-adjacent leaves and other plant material are based on the weight after drying.
What is curing in cannabis processing?
Curing is the continued maturation of dried flower in sealed containers that are opened at intervals. The Oregon State University factsheet lists 14 days at 18 °C and 60 % relative humidity for this step.
Sources
§ 9 KCanG – Anforderungen an den privaten Eigenanbau, Bundesministerium der Justiz
Bridges, C.: Post-harvest processing of hemp flowers, Oregon State University Extension Service
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.