Post-Harvest Care: Trimming and Drying

Growing a successful cannabis crop does not end when the buds are ready for harvest. Two post-harvest processes heavily influence cannabinoid and terpene concentrations: trimming and drying. Their timing and technique can lead to significant differences in the final product’s secondary metabolites—and hence its color, flavor, fragrance and potency.

Harvest timing

Before post-harvest care begins, the first step in securing a high-quality cannabis product is harvesting at the right time. Unripe buds lack the potency and cannabinoid and terpene content of mature buds, while delaying harvest risks cannabinoid degradation.

Determining when cannabis is ready to harvest requires careful daily observation of ripening buds. As buds mature, trichomes become more prominent, resin caps swell and a sticky liquid accumulates. When trichomes transition from clear to a white, cloudy or milky color (Figure 1), cannabinoid composition has peaked, resulting in high THC. Avoid waiting until trichomes turn grey, which indicates that the THC has degraded and harvesttime has passed.[1]

Figure 1. Morphological appearance of white, cloudy or milky trichomes. Image source: Al Ubeed, Hebah Muhsien Sabiah, Ronald B. H. Wills, and Jayani Chandrapala. 2022. “Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review.” Molecules 27 (5): 1719. https://doi.org/10.3390/molecules27051719.

The color of the hair-like structures[2] on the flower is another important indicator (Figure 2). When 75% of the hairs change from pastel to light brown or amber, CBD levels have peaked, signaling the plant is ready for harvest. A digital microscope with 60x magnification and UV and LED lighting can help assess trichomes and budding mass.[3]

Figure 2. When 75% of the “hair” on cannabis flowers turn amber or light brown, the plant is ready to be harvested. While these are technically the stigmas, they’re often referred to as pistils. Image provided by Freepik.

Buds tend to ripen simultaneously on smaller cannabis plants, while larger plants see the outermost 3–6 inches mature before the interior buds.[4]

Trim or dry first?

After harvest, two processes are essential to preserve bud quality: trimming and drying. Trimming removes extraneous plant material, including stems, fan and sugar leaves[5] from the flowers, while drying reduces moisture to retain potency, flavor and psychoactive properties.

The sequence of these processes impacts cannabinoid and terpene content and therefore depends on the grower’s goals. One study examined how the timing and extent of trimming affect these metabolites, with mild trimming[6] before drying increasing cannabinoid content. The researchers hypothesized that leaving some sugar leaves provided a stress signal that increased cannabinoid production. Conversely, terpene content was highest when cannabis was trimmed after drying. They concluded that growers must prioritize which secondary metabolite to optimize, as “optimizing for both simultaneously appears to be difficult.”[7]

Figure 3 illustrates how trimming aggressiveness and moisture levels influence buds.

Figure 3. Mild wet trimming (a): Stems removed, and the top halves of the sugar leaves near the bud trimmed. Aggressive wet trimming (b): Stems and sugar leaves removed before drying. Wet flower before dry trimming (c). Dry flower that underwent any of the trimming treatments (d), the final form of all treatments. Image source: Brikenstein, Nimrod, Matan Birenboim, David Kenigsbuch, and Jakob A. Shimshoni. 2024. “Optimization of Trimming Techniques for Enhancing Cannabinoid and Terpene Content in Medicinal Cannabis Inflorescences.” Medical Cannabis and Cannabinoids 7 (1): 111–118. https://doi.org/10.1159/000539192.

Trimming

Trimming directly affects the final product’s appearance, terpene concentration and cannabinoid profile and potency. Since fan and sugar leaves contain lower cannabinoid concentrations, removing them increases the overall cannabinoid percentage. When done before drying, trimming also increases surface area, promoting moisture removal.

Trimming can be done manually or mechanically, depending on the scale of the grow operation. It typically involves the following steps:

  • Clip and remove buds from the stem.
  • Snip away small, multi-fan leaves around the buds.
  • Remove any petiole leaves remaining between the flowers.
  • After removing fan leaves, cut individual buds from the branch.
  • Trim the buds.

If wet trimming,[8] remove extraneous material from the buds immediately after harvesting while the plant is fresh and moist. Start by removing the large fan leaves lacking trichomes (Figure 4), then carefully snip away sugar leaves from the buds. Avoid prolonged air exposure during this process, as it can lead to terpene evaporation.

If dry trimming,[9] start by removing the fan and sugar leaves from the buds once they have lost most of their moisture. This is more time-consuming than wet trimming because dry leaves curl tightly around the buds, making them harder to remove. Dry trimming is best suited for smaller batches or when preserving terpene content is a priority.

Figure 4. A cannabis plant: (1) mature bud; (2) stem; (3) fan leaves; (4) sugar leaves; (5) trichomes. Image source: Das, Pabitra Chandra, Alec Roger Vista, Lope G. Tabil, and Oon-Doo Baik. 2022. “Postharvest Operations of Cannabis and Their Effect on Cannabinoid Content: A Review.” Bioengineering 9 (8): 364. https://doi.org/10.3390/bioengineering9080364.

Drying

Cannabis contains approximately 80% moisture at harvest, which must be reduced through drying to preserve the buds’ potency, flavor and psychoactive properties, while controlling microbial activity and enabling long-term storage.[10]

Drying must be done carefully, as heat is the primary cause of cannabinoid decarboxylation, the process by which acidic cannabinoids (e.g., THC-A) are converted into their active forms (THC).[11] Terpenes are also highly volatile and can evaporate under elevated temperatures or prolonged air exposure, diminishing the aromatic and therapeutic qualities of the final product.

Understanding the drying rate is critical to prevent quality loss. Drying occurs in two stages:

  • During the constant-rate stage, moisture evaporates consistently from the plant surface as water replenishes it.
  • During the falling-rate stage, surface moisture becomes unsaturated as internal moisture movement slows, reducing drying efficiency. This stage requires careful monitoring to avoid over-drying.[12]

While modern drying technologies such as intermittent or non-isothermal, conveyor, radio frequency and electrodynamic drying are in development,[13] the most common methods remain slow drying, oven drying and vacuum freeze drying.

Slow drying

Slow drying is one of the earliest drying methods and the most used:

  • The most popular approach is hang drying, where excess stems are removed, and the plants are hung upside down in a well-ventilated room maintained at 18–21°C (64–70°F) with 50–55% relative humidity. A small fan helps circulate air. This method allows water to move slowly from the stem into the buds for evaporation, ensuring uniform drying over 4–6 days until the flowers reach optimal moisture levels.[14]
  • Screen drying is another slow-drying method, where the trimmed buds are laid on trays or screens under the same ambient conditions. This approach typically shortens the drying time by one or two days.[15]
Oven drying

A simple and low-cost method is oven drying, done using a vacuum chamber, vacuum desiccator or drying oven. The oven is preheated to 37°C (98.6°F) for 24 hours to prevent decarboxylation of phytocannabinoids; higher temperatures can reduce cannabinoid yield. This method allows moisture to accumulate in flowers without causing bud dehydration. Buds are dried in batches upside down, making this technique better suited for small grow operations.[16]

Vacuum freeze drying

Vacuum freeze drying begins by freezing the plant at ‒40°C to convert most of the water into ice, preventing foaming when the vacuum is applied. The next step, called primary drying, uses negative pressure from the vacuum to sublimate the ice, removing water without altering the end product’s structure. This is followed by secondary drying to eliminate residual moisture. Vacuum freeze drying is considered the best method for medicinal cannabis as it preserves product quality, prevents microbial activity and retains aroma, flavor and cannabinoids.[17]

Conclusion

Harvest and post-harvest care are essential for preserving cannabis quality. By closely monitoring bud ripening to determine the optimal harvest time, selecting an appropriate drying method and timing trimming to prioritize cannabinoid or terpene goals, growers can produce a premium final product.

Emerald Harvest Team

[1] Al Ubeed, Hebah Muhsien Sabiah, Ronald B. H. Wills, and Jayani Chandrapala. 2022. “Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review.” Molecules 27 (5): 1719. https://doi.org/10.3390/molecules27051719.

[2] Commonly referred to as pistils, but they are technically the stigmas.

[3] Ibid.

[4] Ibid.

[5] Small, resin-coated leaves that grow close to or within cannabis buds.

[6] In this case, mild trimming involved removing the stems completely and trimming the top half of the sugar leaves near the flowers.

[7] Brikenstein, Nimrod, Matan Birenboim, David Kenigsbuch, and Jakob A. Shimshoni. 2024. “Optimization of Trimming Techniques for Enhancing Cannabinoid and Terpene Content in Medicinal Cannabis Inflorescences.” Medical Cannabis and Cannabinoids 7 (1): 111–118. https://doi.org/10.1159/000539192.

[8] Wet trimming, or trimming before drying, is ideal for high-humidity regions because removing extra plant material reduces moisture and helps prevent mold. It also minimizes trichome loss, as fresh trichomes are less brittle than dried ones.

[9] Trimming after drying.

[10] Al Ubeed, Hebah Muhsien Sabiah, Ronald B. H. Wills, and Jayani Chandrapala. 2022. “Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review.” Molecules 27 (5): 1719. https://doi.org/10.3390/molecules27051719.

[11] Das, Pabitra Chandra, Alec Roger Vista, Lope G. Tabil, and Oon-Doo Baik. 2022. “Postharvest Operations of Cannabis and Their Effect on Cannabinoid Content: A Review.” Bioengineering 9 (8): 364. https://doi.org/10.3390/bioengineering9080364.

[12] Ibid.

[13] Ibid.

[14] Al Ubeed, Hebah Muhsien Sabiah, Ronald B. H. Wills, and Jayani Chandrapala. 2022. “Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review.” Molecules 27 (5): 1719. https://doi.org/10.3390/molecules27051719.

[15] Das, Pabitra Chandra, Alec Roger Vista, Lope G. Tabil, and Oon-Doo Baik. 2022. “Postharvest Operations of Cannabis and Their Effect on Cannabinoid Content: A Review.” Bioengineering 9 (8): 364. https://doi.org/10.3390/bioengineering9080364.

[16] Al Ubeed, Hebah Muhsien Sabiah, Ronald B. H. Wills, and Jayani Chandrapala. 2022. “Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review.” Molecules 27 (5): 1719. https://doi.org/10.3390/molecules27051719.

[17] Ibid.

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