Harvest, drying, trimming and curing
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Post-harvest · Procedure

Harvest, drying, trimming and curing

This paper gives all the post-harvest steps, from the harvest of the plants to the sealed flower. It shows when to harvest the plants, how to dry the flower and keep the terpenes in it, and how to prevent mold. It also shows how to remove the leaves without damage to the trichomes, and how to do the curing until the water activity is stable. After you read this paper, you will know the target number for each step and a method that you can do again.

Post-harvest9 diagrams4 sources~14 min to read
In this paper
01 Purpose and scope02 Definitions03 Evidence and limitations04 Time of harvest05 Harvest method and weight of the wet plant06 Drying environment07 Water activity08 Trimming and trichome protection09 Curing and storage10 Troubleshooting11 Expected results and limitations12 References
Start here

Purpose and scope

Post-harvest is all the steps that you do after you cut the plant: drying, trimming, curing and storage. An error in these steps can cause damage to the results of many weeks of careful cultivation. The damage can occur in a small number of days. If you dry the flower too quickly or too much, the aroma and the weight decrease. If you dry the flower too slowly, or the flower is too wet, mold starts.

Keep the flower in a small safe zone. The flower must be sufficiently dry to prevent mold growth, but it must not be too dry. If the flower is too dry, the aroma and the weight decrease. A very dry flower has less mass for sale, but a correct control of this stage keeps this mass. Most growers dry the flower too much when they do not want to. Thus supplier figures show that the yield can increase by approximately 5 to 10%.[8]

The post-harvest steps, from start to end1Harvestcut plants atmaturity→2Hang-dry60F / 60% RH,10-14 days→3Takedowncut in sectionsat 0.60-0.62 aw→4Trimremove leaves,keep trichomes→5Cure, burpaw becomes0.58-0.60→6Seal and keepstop burping,completedEach step has a target number. Drying has a room target. Curing has a flower target.
Figure 1. In these five steps, the plant becomes a completed product that is stable. The figure shows the target number for each step. The next sections give more information about each step.
Who this is for

This paper is for you if you do your initial harvest and want results that you can get again. It is not necessary to know the post-harvest procedure before you read this paper. The paper gives a definition of each term where you first read the term. You can use this paper with the mold-risk and airflow-design papers.

The terms

Definitions

Two of these terms are the most important in this paper. It is not necessary to know the terms at this time. Each term occurs again in the next sections.

Water activity (aw)Water activity shows how available the water in the flower is, on a scale of 0 to 1.00. It is the best indicator of mold growth. Water can move between the flower and the air around it. When this movement stops, multiply the water activity by 100 to get the relative humidity of the air.[6]
Moisture content (%)The percentage of the total weight of the flower that is water. It gives information about the yield, but not about the safety. It is a different number from the water activity.
Relative humidity (RH)The quantity of water vapor in the air, from 0 to 100%. The target for the dry room is 60% RH.
TrichomesThe glands of resin on the flower. They contain the THC, the terpenes and the flavonoids. Prevent damage to the trichomes in each step. If you touch the flower, you can remove trichomes from it.
TerpenesThe oils that give each cultivar its aroma and flavor. They evaporate if the flower becomes too dry.
BurpingA short opening of a sealed container during curing. The opening lets moist air go out of the container and lets new air go into it.
Two numbers about water that have different tasks1Water activity0-1.00 scale ·shows MOLD risk· controls theprocedure→2Moisture content% of weight ·shows YIELD ·measures theproductWater activity shows when the flower is safe and completed. Moisture content shows how much you have.
Figure 2. Water activity is the number that you use to control the procedure. Moisture content is the number that you give in a report. A frequent error of new growers is to use one number for the task of the other number.[8]
Burping decreases jar humidity to the targetOpen the jars each day at the start of the cure to release moisture. Open them less when the jars hold the target band.target 58-62%5056616672seald1d2d3d4d5d6jar RH %
Diagram. Burping removes moisture at the start of the cure. Do this until the humidity in the jars stays at the target value.
Quality of the information

Evidence and limitations

Three types of information

We want each paper to be correct. Thus we examine each paper for information that is not solid. This information comes from the view of one grower, from a small number of sources, or from grower methods that have no controlled test. We identify this information, and we do not show it as solid.

Frequently there is no paper for the decision that you must make. Then we use the reports of other growers and the methods that work in the rooms that we know. This information can help you, but it is not the result of a laboratory test. Use the methods that work for your plants, for your room and for your meters. If a table does not agree with your crop, use the data from your crop and record the difference.

Solid
Tests of plants, specifications or many sources that agree show that the information is correct
  • Water activity is a better indicator of the risk from microbes than only the moisture percentage. For flower, an ASTM-type range is 0.55 to 0.65.
  • Slow drying in darkness at a cool temperature keeps more terpenes than fast drying at a hot temperature.
  • In storage, light and heat increase the rate of degradation of cannabinoids and terpenes.
Grower method
Many growers use this method in their rooms. Start with it, then change it for your room.
  • Usual values of 60 °F and 60% RH for drying, and the procedure to hang all of the plant.
  • Many rooms select dry trim when quality is important.
Weak
The view of one grower, a small number of sources, one test, or a method that works in one room
  • A supplier value of 5 to 10% yield recovered as the result of tests at many sites with peer review.
  • The quantity by which trimming decreases the water activity (aw) as one value for all conditions.

If you find an error, make a report. We will correct it. Make the report on GitHub, with the name of the paper and the information that is incorrect. If you have a source, include it: Make a report of an accuracy problem. The regulations, labels and licenses of your area always override each procedure in these papers. The label weak in a paper shows the points where the risk of an error is highest.

Step 1, the information

Time of harvest

Harvest is the procedure in which you cut all the plants after they complete the flowering. Examine the flower to find the maturity of the plants. Do not use the date on the calendar.

The trichomes are the best signal of maturity. Examine the trichomes with a loupe. They are first transparent, then cloudy, then amber when the maturity increases. The change of color shows the maturity of the resin glands.[1] A usual procedure uses a set time for the flowering, with plant-work stages at days 7 to 10, 21 to 28 and 42 to 49. At the end, you cut the plants.

  • Harvest is the procedure in which you cut all the plants after they complete the flowering.
  • Cut one cultivar at a time, in the sequence on your list of cultivars. Thus the cultivars do not mix.
  • Keep the tag of each plant attached when you cut the plant. The tag gives traceability of the batches.
  • Collect the loose buds that fall on the table. Put a label on the buds of each cultivar and dry them independently.
Harvest is the end of a specified flowering cycleEach stage is a task with a set time. Harvest is the last task.01346trellis d1lollipopping d7-10defanning d21-28last defanning d42-49harvestplant-work stage
Figure 3. Harvest is the end of a set sequence of plant-work stages in the flowering room.
Use the plant for the decision

If the calendar shows that you must cut the plants, but most of the trichomes are transparent, wait. Examine the flower to find the maturity. The date gives only an approximate indication.

Step 2, the procedure

Harvest method and weight of the wet plant

Cut each whole plant and hang it to dry. Do not remove the buds from the plant first. Release each plant from the bottom two layers of the trellis net (the net that holds the plant). Keep the top layer on the plant. The layer holds the plant. Then cut the primary stalk at the bottom.

Before you hang the plants, weigh each bin to record the wet weight. The wet weight is the initial weight. After the drying, compare the wet weight with the last dry weight. Thus you get the dry-to-wet ratio for each cultivar. The dry-to-wet ratio is approximately 10% of the wet weight of the whole plant (one example batch gave 10.46%). It shows how much of the mass of the harvested plants is water.

  1. 1
    Release the plant
    Cut around the plant through the bottom and middle layers of the trellis net. Keep the top layer attached to hold the plant.
  2. 2
    Cut the stalk
    Cut the primary stalk at the bottom. Then you can remove the plant in one piece.
  3. 3
    Fill the bin
    Put 7 to 10 whole plants in each bin of 208 L (55 gal). Do not put too many plants in the bin. Too many plants cause damage to the flower.
  4. 4
    Weigh the wet plants
    Set the scale to zero when the empty bin is on it. Then weigh the bin with the plants to record the wet weight. The wet weight is the baseline for all the yield records.
Water in the plant when you cut itExample batch: dry weight was approximately 10.46% of wet weight. The remaining weight was water.0295786115100%Wet weight10.46%Dry weight
Figure 4. Approximately 90% of the weight of a plant when you cut it is water. The water must move out of the plant during the drying. When you hang the whole plant, the water moves out more slowly, and the moisture moves out of the stem at the same rate.
Meters for water activity and moisture, with dried buds
Example. The same moisture content can have different water activity values, from a dry value to a value with mold risk. Use aw (here approximately 0.61) to control the post-harvest procedure, and not only the moisture content.Fact check
The primary information

Drying environment

Keep the dry room at 16 °C (60 °F) and 60% RH, with the fans on and the lights off. Clean the room fully before you put the plants in it. At these setpoints, the takedown of whole plants is usually possible after 10 to 14 days.[8]

Slow drying in a cool room keeps the terpenes. Terpenes evaporate in heat and in dry air. Slow drying also prevents the condition where the outer part of the bud is dry and the inner part stays wet. This condition is the usual cause of mold in the bud that you cannot see.

Keep the light off, because light causes the degradation of cannabinoids and terpenes with time.[4] The best drying method can have small differences for different cultivars. Thus the setpoints are a good start point, but they are not correct for all cultivars.[2]

  • Setpoints: 16 °C (60 °F), 60% RH, fans on, lights off, doors closed. Keep the number of persons that go into the room as small as possible. Thus the environment stays stable.
  • The drying of whole plants is approximately 10 to 14 days at these setpoints.
  • If the RH in the room is more than 60% and the dehumidification is too small, exhaust fans can decrease the humidity.
  • Keep an equal space between the racks. Thus the air flows to each plant and the buds dry at the same rate. Clean the room fully before each load.
The humidity in the dry room decreases until the takedownKeep the room in the green zone. The curve decreases when the load dries.target 60% RHhigh humidity: mold risktoo dry: terpenes evaporate5256606468day 0day 3day 5day 8day 11day 14room RH %
Figure 5. The green zone is the target of 60% RH. If the RH increases to a value more than the green zone, the risk of mold increases. If the RH stays less than the green zone for a long time, the terpenes start to evaporate.[8]
The primary information

Water activity

After the hang-dry, some moisture stays in the flower. Some moisture is more dangerous than other moisture. The plant material holds some of the water in its inner part, and this water is not dangerous. The free water at the surface is the water that microbes use.

Water activity (aw) shows how available the remaining moisture is to microbes, on a scale of 0 to 1.00. Mold and yeast can increase in number at 0.70 aw and higher. Bacteria that cause disease can increase in number at 0.85 aw. The risk increases quickly near these thresholds. If the aw is less than approximately 0.55, the quality frequently decreases, although the growth of microbes becomes slower. The ASTM range of 0.55 to 0.65 is the target for dry flower.[7]

The growth of microbes gives the maximum value of this range. Quality gives the minimum value. If the aw is less than 0.55, the terpenes evaporate and the quality decreases.

These two limits give a range of 0.55 to 0.65 aw. This range is the same as the range in the ASTM D8197 standard for dry cannabis flower.[5] Start the testing of samples at approximately day 7 to 8. The takedown is the removal of the plants from the racks. Do the takedown when the average aw of the batch is 0.60 to 0.62. Thus there is headroom to the 0.65 mold limit.

Safe zone of water activityDo the takedown in the green zone, at approximately 0.60-0.62 aw, with headroom to the 0.65 mold limit.too drytakedown at 0.60-0.62mold and yeastbacteria0.50.70.9
Figure 6. If the aw is less than 0.55, the terpenes evaporate. If the aw is more than 0.65, there is a risk of mold. The takedown of the batch is at 0.60 to 0.62 aw.[5]
Water activity thresholds for microbe growthThe takedown target (0.62 aw) is less than each growth threshold. The difference is the headroom.00011target0.6 awNo growth0.7 awMold and yeast0.85 awBacteria
Figure 7. Decrease the aw of the batch to a value less than the 0.70 aw mold limit. The takedown target of 0.62 aw gives headroom.[7]
Water activity is better than a low-cost moisture meter
  • Water activity is the better number for control, because it has much less variation than the readings of a low-cost moisture meter.
  • In one example, the measurement of water activity gave a yield precision that was approximately 10 times better (from ±1% to ±0.12%).
  • Flowers with a high density usually have a lower aw at the end of the drying than flowers with a low density. The difference is small. Use the meter as an indication, and also smell the flower.
Water activity (aw): the mold limitaw is the free water that microbes can use. Cure to approximately 0.55-0.65: stable, good to use, below the mold limit.dry / stablecure targetriskmold growth0.30.60.9
Diagram. Dry and cure the flower to a water activity at which the product is stable and good to use. The water activity must be below the value at which mold growth is possible.
Step 3, the procedure

Trimming and trichome protection

Trimming removes the leaves from the bud, and thus the bud is clean. There are two times for the trimming. Wet trim is the trimming immediately after you cut the plants, before the drying. Dry trim is the trimming after the hang-dry. A dry trim makes the drying slower, and it causes less damage to the oils that give the aroma. Thus many facilities select a dry trim to keep more of the terpenes.[3]

Do not touch the flower. If you touch the flower, you remove the trichomes that contain the potency and the aroma. Then the buds have a smooth, matt surface.

To do a dry trim, do the takedown. Then cut the plants into sections of 20 to 30 cm (8 to 12 in). Remove the large fan leaves with your hands. Then cut the smaller sugar leaves with scissors. When resin collects on the scissors, clean them in 71% alcohol.

  • Bucking is the procedure in which you cut the buds from the stem after the trimming. Do the bucking into a sealed bag. Thus the flower does not become too dry in open air.
  • Do not touch the flower. If you touch the flower, you cause damage to the trichomes.
  • Remove the fan leaves with your hands (large leaves with a small number of trichomes). Then cut the sugar leaves with scissors.
  • When resin collects on the scissors, clean the scissors in 71% alcohol.
  • After a dry trim, measure the aw again. If you touch the flower and remove the leaves, the reading can change. Thus do not think that the aw from the hang-dry is correct.
Wet trim compared with dry trim. This paper uses a dry trim, because it keeps more terpenes and the drying causes less damage.[3]
Wet trimDry trim (this paper)
TimeDirectly after you cut the plantsAfter the hang-dry of 10 to 14 days
Drying speedFaster, with more damage to the flowerSlower, with less damage to the flower
Leaf removalEasier (the leaf is soft)The leaf breaks easily. You must be more careful.
Terpenes that you keepLower (you touch the flower more, and the drying is faster)Higher. Thus growers select a dry trim.
Risk of damage when you touch the flowerMoreLess
The primary information

Curing and storage

Curing makes the water activity the same in all the flower of the batch. It also keeps the terpenes. Without curing, there can be degradation of the terpenes in storage.

Keep the flower in containers at 16 to 18 °C (60 to 65 °F) and 58 to 62% RH. Read the humidity sensor. When the reading of a bin is more than approximately 60% RH, burp the bin. Remove the lid for 5 to 10 minutes. Then turn the barrel. Record the reading.

When the flower after the trimming is at 0.58-0.60 aw, you complete the curing. Seal the flower. Stop the burping. More burping only makes the terpenes and the water evaporate. Thus the aroma and the weight for sale decrease.

Curing also keeps the cannabinoids more stable, because you keep the product at a low temperature and without light. These conditions decrease the speed of the degradation during storage.[4]

The burp decision each day1Read sensormeasure binhumidity→2More than 60% RH?if yes, burp5-10 min→3Turn, recordturn barrel,recorddate/RH/bin→4At 0.58-0.60 aw?if yes, seal,stop burpingDo the steps each day until the aw is 0.58-0.60. Then seal and keep it.
Figure 8. Burp the bin while the flower is wet. Turn the barrel to dry the flower at the same rate. Record each burp. Stop when the flower is at 0.58-0.60 aw.
Too many burps decrease the weight for sale

When the flower after the trimming is at 0.58-0.60 aw, seal it. Each burp after this point makes the terpenes and the water evaporate. As a result, the aroma and the weight for sale decrease. Remove the air from the bags, but do not compress the flower. Do not put bags on top of other bags. Thus there is no damage to the structure of the buds.

When there is a problem

Troubleshooting

Most post-harvest problems have one of three causes: the drying is too fast, the flower is too dry, or the space is too full. Too much drying can cause damage that you do not see. A low-cost moisture meter with an error of ±1% can show a reading of ‘11% moisture’. At this reading, the aw of the flower can be from 0.53 aw (too dry, with damage to the flower) to 0.66 aw (mold risk). Thus growers who use one number frequently dry the flower too much, and the weight and the aroma decrease.[5]

One '11% moisture' reading does not show the awA meter with +/-1% error gives an aw from 0.53 (too dry) to 0.66 (mold). A water activity reading gives only 0.617 to 0.623.000110.53 awMeter low0.66 awMeter high0.617 awaw reading low0.623 awaw reading high
Figure 9. The same reading of ‘11% moisture’ can show a flower that is too dry and has damage, or a flower with a risk of mold. Water activity makes this range very small.[5]
The six primary post-harvest errors and their corrections.
ErrorResultCorrection
Too much drying, to less than 0.55 awThe terpenes evaporate, the aroma decreases and the weight of water decreasesDo the takedown at 0.60-0.62 aw. Stop the curing at 0.58-0.60 aw.
Drying that is too hot or too fastThe outer part becomes dry and the inner part stays wet. Mold can start in the inner part, and you cannot see it.Keep 16 °C (60 °F) and 60% RH. Let the plants dry for 10 to 14 days.
You use only a low-cost moisture meter for the decisionAn error of ±1% gives 0.53-0.66 aw, from too dry to a risk of mold.Use a water activity test to find when you can complete the procedure.
Containers that are too fullThe weight compresses the buds, and the moisture cannot move out of them.Fill totes and barrels to a maximum of approximately 2/3. Fill curing barrels to a maximum of half.
You touch the flower, or you do not clean the room fullyYou remove trichomes from the flower, and there is contamination.Touch only the stem. Clean the room fully before each load.
The aw is safe, but you smell that the flower is wetThe inner part is not dryLet the flower dry more. Smell the flower and feel it for the last check.
Typical results

Expected results and limitations

The hang-dry is approximately 10 to 14 days, and the curing is some more days. After the curing, the flower is a completed product. All of the post-harvest stage is two to three weeks. It is not fast, and you cannot make it faster.

The end of the post-harvest stage, day by dayTesting starts near day 7-8. Takedown is near day 10-14, at 0.60-0.62 aw. Cure to 0.58-0.60 aw, then seal.safe zone 0.55-0.65 aw01111harvest d0test d7-8takedown d10-14trim, curesealedaw
Figure 10. A typical curve shows the water activity. It decreases from the harvest, moves into the safe zone at the takedown, and becomes stable in the curing before you seal the batch.[5]
Three primary items
  1. The post-harvest stage is weeks, not days. Use two to three weeks for the stage. Do not make the drying faster.
  2. Do not dry the flower too much. If you control the drying and the curing correctly, you keep the weight for sale. The figures of approximately 5 to 10% from suppliers are only examples.[8]
  3. The cultivar is important. The drying and the curing are different for each cultivar. Flowers with a high density and flowers with a low density have a different aw at the end. The difference is small. Thus record each batch.[2]

Record the aw, the RH, the dates and the results for each cultivar. Thus you can get good results again. The instrument gives an indication and does not make the decision. In the safe aw zone, smell the flower and feel it to make the last decision. Read the mold-risk paper for the procedure if the aw of a batch is more than the mold limit. Read the nutrient-mixing paper for the feed, which has an effect on the quality.

Related papers
Mold risk
Find and stop bud rot
Airflow and fans
How much air to move, and where to put the fans
Mix nutrients
Mix salts correctly, in liters and kilograms

References

  1. Punja, Z.K., Sutton, D.B., & Kim, T. (2023). Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research, 5(1), 12. https://doi.org/10.1186/s42238-023-00178-9 https://doi.org/10.1186/s42238-023-00178-9
  2. Birenboim, M., Brikenstein, N., Duanis-Assaf, D., Maurer, D., Chalupowicz, D., Kenigsbuch, D., & Shimshoni, J.A. (2024). In Pursuit of Optimal Quality: Cultivar-Specific Drying Approaches for Medicinal Cannabis. Plants (Basel), 13(7), 1049. https://doi.org/10.3390/plants13071049 https://doi.org/10.3390/plants13071049
  3. Brikenstein, N., Birenboim, M., Kenigsbuch, D., & Shimshoni, J.A. (2024). Optimization of Trimming Techniques for Enhancing Cannabinoid and Terpene Content in Medical Cannabis Inflorescences. Medical Cannabis and Cannabinoids, 7(1), 111-118. https://doi.org/10.1159/000539192 https://doi.org/10.1159/000539192
  4. Fairbairn, J.W., Liebmann, J.A., & Rowan, M.G. (1976). The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology, 28(1), 1-7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x https://doi.org/10.1111/j.2042-7158.1976.tb04014.x
  5. ASTM International. (2021). ASTM D8197-21: Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower Intended for Human/Animal Use. West Conshohocken, PA: ASTM International. https://www.astm.org/d8197-21.html (source not from a journal, for example from a manufacturer) https://www.astm.org/d8197-21.html
  6. U.S. Food and Drug Administration. Inspection Technical Guides: Water Activity (aw) in Foods. Office of Regulatory Affairs, FDA. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/inspection-technical-guides/water-activity-aw-foods (source not from a journal, for example from a manufacturer) https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/inspection-technical-guides/water-activity-aw-foods
  7. AQUALAB (Addium, Inc.). How Water Activity Controls Microbial Growth. AQUALAB Learning Center. https://aqualab.com/learn/how-water-activity-controls-microbial-growth (source not from a journal, for example from a manufacturer) https://aqualab.com/learn/how-water-activity-controls-microbial-growth
  8. AROYA (Addium, Inc.). Processor's Guide to Moisture and Water Activity (Drying Cannabis). AROYA Education Guides. https://aroya.io/education-guides/drying-cannabis (source not from a journal, for example from a manufacturer) https://aroya.io/education-guides/drying-cannabis

Each citation in the paper, for example [1], refers to an item in this list. Each item is a primary source or an instruction from an authority, unless the item shows a different type. The results of cannabis tissue culture change much with the genotype. Before you use the dilutions, hormone doses and local regulations, make sure that they agree with the primary sources.