Drying and Curing CBD Flowers: A Grower's Complete Guide
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By Quentin, CBD hemp grower – updated October 2026
Six months of growing… and two weeks to ruin it all. Drying is the shortest stage of the year, but it decides whether the aromas you worked on all season make it into the bag. Here is everything I do in my drying room: the settings, the equipment, the pitfalls, and the only real way to know whether a flower is dry.
The essentials in 30 seconds
- Dry in the dark, at 16°C and 58 to 60% humidity, which gives a VPD between 0.6 and 1 kPa.
- Only bring inspected material into the drying room: a damaged flower is removed whole.
- Size the dehumidifier first (rated capacity divided by two), then the air conditioning.
- Keep air moving everywhere, without ever blowing on the flowers.
- Check your hygrometers with salt and measure water activity in a jar: aim for 0.55 to 0.65.
- Curing refines a well-dried flower; it never makes up for a failed drying.
The goal of drying: remove water, keep the aromas
Drying means removing water from the flower without degrading its active compounds or its aromatic molecules. A fresh flower contains 75 to 80% water depending on the variety. You don't want to remove all of it: the target is a final moisture content of 8 to 12%, 14% at most. Weigh your flowers before and after: their weight is almost divided by four.
A flower is not uniform: the stem, the bracts, the core and the surface don't lose water at the same rate. That's why a wood moisture meter is useless on a flower. We'll see below how to measure properly.
Before drying: sort without mercy
Before anything goes into the drying room, I inspect each plant flower by flower, on a separate table: mould, caterpillar droppings… A damaged flower is removed whole, not just the affected part. A visible patch of mould is often the tip of the iceberg, and by trying to save 1 g, you contaminate 20.
The right settings: darkness, 16°C and 60% humidity
Dry in the dark: light and UV degrade active compounds and aromas, and a flower exposed to the sun ends up turning brown.
Terpenes evaporate no matter what; you can only control how fast. The cooler it is, the better they keep: 16°C is ideal, you can go up to 20°C without losing too much, and beyond that the aromas disappear much faster.
Temperature isn't enough: you have to control humidity. VPD (vapour pressure deficit) combines the two and expresses how strongly the air "pulls" water out of the flower. Keep it between 0.6 and 1 kPa; at 16°C and 60%, you're at 0.73 kPa. My VPD temperature and humidity chart gives every combination.
A good VPD is not enough:
| Conditions | VPD | Result |
|---|---|---|
| 16°C, 60% | 0.73 kPa | Ideal |
| 20°C, 60% | 0.94 kPa | Possible, at the upper limit |
| 20°C, 69% | 0.73 kPa | Flower never dry enough, risk of mould |
| 16°C, 50% | 0.91 kPa | Flower too dry, brittle |
Sizing your drying room
The size of the drying room determines everything else: better slightly too big than running out of space in the middle of harvest. Mine is 4 m by 7 m and 2.5 m high, so 70 m³ to keep in the right conditions for the 10 to 14 days of drying.
The dehumidifier first
Divide the advertised capacity in litres per 24 hours by two: it is measured at around 30°C and 80% humidity, nothing like a drying room at 16°C. For 100 kg of fresh flowers, count roughly 18 L on day one, 17 L on day two, 13 L on day three, 10 L a day up to day six, then 7 L a day up to day fourteen (source, p. 8).
100 kg brought in at once therefore needs a dehumidifier rated at 36 L/24 h at the very least. If you bring in your harvest in several batches, the peaks overlap: two batches of 100 kg one day apart means 35 L to remove and a 70 L/24 h unit. Add 20% for the outside air coming in. My dehumidifier sizing calculator does the maths for you.
Then the air conditioning
A dehumidifier is a refrigeration machine: it cools the air to condense its water, but releases all its heat into the room. Its electrical power adds to that of the other appliances, and the air conditioning has to offset all of it, plus the input from outside air, with a 30% margin. Simple rule: the more powerful the AC, the closer you'll stay to 16°C. Mine is 15,500 BTU; when it's over 28°C outside, the best I can get is 18°C.
Air circulation
Warm and cold air don't mix well, and neither do dry and humid air. There must be no pockets of humid, stagnant air: I use a circulation fan near the AC and the dehumidifier, wall fans all pointing the same way for a perimeter airflow, and extractors spread around the edges. Fans everywhere, but never pointed at the flowers: terpenes don't like gusts of wind.
Hanging, on racks or hybrid?
| Method | Pros | Cons |
|---|---|---|
| Whole plant hanging | Simple, fast harvest, hardly any equipment | Takes a lot of space, airflow hard to even out, core of the plant stays wetter |
| Flowers on racks (my method) | Little handling once dry, sorting by size, saves space, straight to curing | Much longer harvest, demanding climate control, investment |
| Hybrid (branches, large leaves removed) | Good compromise on time and space | A lot of handling once dry |
A myth along the way: the stem does not act as a "water reserve" that improves quality. Terpenes are volatile, and drying too slowly is no guarantee of quality. Trim wet or dry? Without trimming, the flower dries more slowly and stays vulnerable longer; with trimming, every cut is an entry point for spores. The risk is the same. A perfectly controlled method is as good as any other perfectly controlled method.
The pitfalls that ruin a dry
Drying too fast. Too warm or too dry, the surface sets before the core and the water stays trapped inside. The flower seems dry, then the water comes back out in the jar and causes mould. And the terpenes leave faster.
Drying too slowly. Too humid, the flower stays wet for days. Botrytis (grey mould) develops between roughly 10 and 27°C, with an optimum around 20°C (source). At 16°C, you're within its range: it's controlled humidity that protects you, not the cold.
Trusting a single sensor. A hygrometer measures the air around it, not the whole room. Add more measuring points to find the pockets, and adjust the airflow.
Letting the dehumidifier control itself. Its built-in humidistat measures the air entering the machine, often roughly. Set it to continuous mode and control it with a smart plug linked to a sensor placed at flower height. Check that it restarts on its own after a power cut, and leave a gap between the off and on values.
Calibrating your hygrometer with salt
- In an airtight box or a zip bag, place a small dish of table salt with a few drops of water: a damp paste with some undissolved salt left.
- Put your sensors next to it, without touching the salt, and close.
- Wait at least 8 hours, ideally overnight, at a stable temperature.
- An accurate sensor reads about 75% (source). If it reads 71%, it is 4 points low: correct the offset.
Repeat the test before every drying season, even with a new sensor.
How do you know a flower is really dry?
The snapping-stem test isn't enough: it tells you about the stem, not the core of a big flower. What you need to measure is water activity (aw), meaning the free water that mould can use. The right range for a dry flower is 0.55 to 0.65 (ASTM D8197 standard). Above 0.65, mould can grow in the jar; below 0.55, the flower crumbles, the trichomes fall off and the aromas have suffered. In 2024, one of my batches rose to 0.70 in a curing container: I caught it in time and put it back in the drying room.
No need for lab equipment: fill a clear airtight jar three-quarters full with a representative sample of the batch, slip in a calibrated hygrometer, close it, and leave it for at least 12 hours, ideally 24, in the drying room so the temperature stays stable. The humidity reading divided by 100 gives the aw: between 55 and 65%, it's ready; above that, back to the drying room.
That's also why I set my drying room to 60%: a flower that stays there long enough ends up in equilibrium, at around 0.60. On my 2026 harvest, my batches measure between 0.56 and 0.62 depending on the variety.
Curing in brief
Curing is not drying. In the jar, water spreads between the core and the surface until it reaches equilibrium: it is first and foremost a homogenisation. Opening your jars ("burping") is mainly useful to release humidity when the jar's hygrometer goes above 65%; if the flower went in at the right water activity, there's almost nothing to release.
On the biological side, enzymes break down chlorophyll and starch as long as there is enough water and active cells, which fades the grassy notes. But curing creates no terpenes: it reveals the ones that are left (see my article on hemp terpenes). And if drying was too fast or went too far, these changes stop for good: curing never makes up for a failed drying.
To see the result: the shop's outdoor CBD flowers.
Frequently asked questions
How long does it take to dry CBD flowers?
In my drying room, at 16°C and 60% humidity, count 10 to 14 days. Water activity tells you when it's done, not the calendar.
What temperature and humidity should you dry at?
Ideally 16°C (20°C at most) and 58 to 60% relative humidity, in the dark, with a VPD between 0.6 and 1 kPa.
How do you know if a CBD flower is dry enough?
Place a sample in a closed jar with a calibrated hygrometer and wait 12 to 24 hours. Between 55 and 65% humidity, the flower is ready.
Should you open your jars every day during curing?
No. Open them when the jar's hygrometer goes above 65%. If the flower went in at the right water activity, there's almost nothing to release.
CBD flowers sold in France must contain less than 0.3% THC.
CBD products are not medicines and are reserved for adults.
Quentin, CBD hemp grower – L'Herbe Enchantée