Growers in Thailand report meters reading 99% overnight in the wet season. The widely recommended slow dry runs at about 18–21 °C and 55–62% relative humidity (RH). Here, that condition does not occur naturally at any hour of any day. One tonne (1,000 kg) of wet flower at 80% moisture holds about 778 litres of water that must be removed to bring it down to 10%. This article works out where that water goes. It then ranks five setups Thai growers actually use, from a traditional open-eave barn to a small controlled chamber, by cost, capacity and what each one gives up.
1. Start with the water, not the equipment
The single most useful number in drying is not a temperature or a humidity setpoint. It is the mass of water you have to move.
Drying typically takes plant material from about 80% moisture content at harvest to about 10% for storage, on a wet basis (water as a share of total fresh weight). The dry matter stays the same, so:
- Water to remove = wet mass × (1 − 0.20 ÷ 0.90) ≈ wet mass × 0.78
- 5 kg wet → about 3.9 L of water
- 20 kg wet → about 15.6 L
- 100 kg wet → about 78 L
- 1,000 kg wet → about 778 L (1 L of water ≈ 1 kg)
This matches the ratio in University of Vermont Extension’s drying guide: 39 lb of water per 50 lb of wet crop.
Those figures are climate-independent. They are arithmetic about the crop.
The figure in the same source that does not transfer is the ventilation one. A 36-inch (about 0.9 m) fan moving 10,000 CFM (about 17,000 m³/h) is quoted as carrying about 250 lb (about 113 kg) of water per hour on 55 °F (about 13 °C), 60% RH intake air. That rises to about 700 lb (about 318 kg) per hour if the air is heated to 80 °F (about 27 °C). The calculation depends entirely on the intake air having room to take up moisture. At 30 °C and 85–95% RH, incoming Thai air has almost none. Flower moves towards equilibrium with the air around it. Air already at 85–95% RH cannot pull flower below a water activity of roughly 0.85–0.95, however much of it you move. Ventilation-based drying is the default method in most extension literature and most grower guides, and it is simply unavailable to you in the wet season. The load moves onto refrigerant dehumidification, and you also pay to cool any outside air you let in.
This is the sentence to take away: a Thai dry room needs roughly the dehumidifier capacity a temperate room needs, plus the cooling to condition any outside air that gets in. And it cannot fall back on air exchange when the dehumidifier is undersized.
2. What growers here actually report
Evidence from Thailand-resident growers, so the problem is described rather than assumed:
- “Humidity reached 99% overnight according to my meter, optimum for drying is 45–55%.” (ASEAN NOW, “Is it possible to dry buds outside in Thailand?”) The 45–55% figure is that grower’s opinion. This article uses one target band throughout: about 55–62% RH at 18–21 °C, finishing the flower at a water activity of roughly 0.55–0.65. Drying much below that band speeds the dry and risks over-drying. Staying above it is the main risk in this climate.
- A dedicated high-humidity drying thread on THCFarmer proposes answers ranging from traditional open-eave barns to under-stair cupboards to newspaper wrapping to spacing individual branches. The range of answers is itself the finding: there is no settled method.
- Budget hardware sold in Thailand: Xiaomi and Widetech 18-litre units at 4,700–5,000 THB on Lazada at the time of that thread. They are reported to take a room from 55–60% down to 40–45% RH, with an explicit warning that build quality is a gamble (ASEAN NOW, “Dehumidifier for drying”).
- Commercial-grade reference point often mentioned by growers: the Quest 70. Its manufacturer rates it at 70 US pints (about 33 L) per day at 26.7 °C / 60% RH (80 °F / 60% RH), falling to 43 pints (about 20 L) per day at 23.9 °C / 50% RH. The manufacturer lists it only as a 110–120 V / 60 Hz unit (Thai mains is 220 V / 50 Hz) and has discontinued the model. Treat it as a capacity benchmark, not a shopping recommendation.
3. The five setups
Ranked from cheapest to most controlled. Cost figures are the ones reported by growers in the threads cited. They are indicative, not quotes, and hardware prices in Thailand move.
Setup 1 — Traditional open-eave barn or airy roofed space
What it is: hanging in a shaded, roofed, open-sided structure with continuous cross-breeze, as used for other Thai agricultural drying.
Capacity: large, in the sense that you can hang a lot. Control: none.
What actually happens in the wet season: the space tracks ambient. At 85–95% RH the flower does not dry. It sits at high water activity for days, where moulds such as botrytis and Aspergillus can colonise it. Growers who report success with this method are almost always describing the cool dry season (roughly November to February, varying by region), when ambient air can genuinely fall into a usable band overnight.
Verdict: viable for dry-season harvests only. In the wet season this is not a slow dry, it is a slow spoil.
Setup 2 — Small sealed room with one or two consumer dehumidifiers
What it is: a closed bedroom or storeroom, 18 L/day consumer dehumidifiers, a fan for air movement, no cooling.
Cost: 4,700–5,000 THB per unit, as reported.
Capacity, done properly: compare the unit’s real litres per day against the batch’s total water load spread over the dry. Do not compare it with “kg of crop per day”.
- Rating conditions differ. Many consumer units sold in Asia are rated at warm, wet test conditions (commonly 30 °C / 80% RH; check the label or manual). US pint ratings use a different standard (26.7 °C / 60% RH). At drying conditions of 18–21 °C and around 60% RH, any refrigerant dehumidifier removes noticeably less than its label figure. The Quest 70’s own ratings show the effect: about 33 L/day at 26.7 °C / 60% RH, but about 20 L/day at 23.9 °C / 50% RH.
- Worked example: 20 kg of wet flower holds about 15.6 L of water. Over a 7–10 day dry that averages about 1.6–2.2 L per day, with more than the average coming off in the first days. One 18 L-label unit, even well below its rating, has headroom for the crop itself. What overloads it is humid air leaking into a poorly sealed room, and a full tank.
- Scale it up: 100 kg wet is about 78 L, or roughly 8–11 L per day on average over 7–10 days, higher at the start. Once real-world output and leakage are counted, that likely needs several consumer units or a commercial-class machine.
Failure modes to plan for: with no cooling, the dehumidifier’s own heat raises room temperature, and drying too warm costs terpenes. Consumer units also have small tanks. If you are not plumbing to a drain, a full tank stops the machine and the room reverts to ambient overnight, which is exactly when ambient is worst.
Verdict: the realistic entry point for a personal-scale grow. Seal the room, plumb the drain, add a fan, and measure the room with your own hygrometer rather than trusting the unit’s display.
Setup 3 — Sealed room with air conditioner plus dehumidifier
What it is: the standard small-commercial answer. The A/C does the cooling, a refrigerant dehumidifier removes the moisture, and both run together.
What matters for drying: air conditioning alone does not hold a dry room in the 55–62% band in this climate. A room that “has A/C” is not a controlled room. Over-specify the dehumidifier; growers in the threads cited agree on this. A refrigerant dehumidifier releases into the room all the electricity it draws plus the heat given off when the water condenses. The A/C has to remove that heat to keep the room at 18–21 °C, so size the cooling with the dehumidifier running.
Cost: an A/C plus a commercial-class dehumidifier, plus power. Get local quotes, and check voltage: many grow-market dehumidifiers are US 120 V / 60 Hz models.
Verdict: this is where genuine control starts. Sizing the A/C and dehumidifier for a whole room is a separate problem from drying and is not covered here.
Setup 4 — Small chamber with tight water-activity control
What it is: a small insulated cabinet or chest holding a modest batch, with humidity and temperature controlled to a narrow band.
Why it appeals here: the smaller the conditioned volume, the smaller the load from outside air leaking in, which is the expensive part in this climate. A cabinet holding 5 kg wet (about 3.9 L of water in total) is a manageable problem in a way that a 40 m² room is not.
The target it aims at: a finished water activity around 0.55–0.65, the band commonly cited as the upper limit for storing dried flower safely.
The Thai-specific inversion: in a dry climate the risk is drifting below the band and over-drying. Here the risk is drifting above it, back towards the water activity at which moulds grow, every time the chamber is opened or its control slips.
Verdict: best control per baht at small scale. It does not scale to a commercial harvest without buying many of them.
Setup 5 — Fast hot-air drying, for biomass destined for extraction only
What it is: forced hot air at around 75 °C for roughly 8 hours, rather than a slow ambient dry.
What the study found: a Cornell study on hemp compared hot air at 75 °C (about 8 h), ambient air drying (about 1 week) and freeze-drying (24–48 h) (Baek, Grab & Chen, Plants 2025). It found that “both drying and curing did not significantly affect the total cannabinoid contents”. Total CBD ranged from about 10.6 to 13.4 g/100 g across methods. Hot air took moisture from 77% to 6% in about 8 hours and caused 8.5–9.0% decarboxylation. It delivered up to a 2-log reduction in total yeast and mould, and its drying rate was about 5× that of freeze-drying.
The two limitations that decide how you may use this: terpenes were not measured, and the material was CBD-type industrial hemp inflorescence (cultivars Hempress and Wild Bourbon), not high-THC premium flower.
Verdict: do not read this as licence to bake premium flower where terpene quality matters. Read it as a defensible answer to a specific Thai problem: biomass headed for extraction, harvested in the monsoon, failing total yeast and mould limits. For that use case, a 2-log microbial reduction with cannabinoids intact is a real result. Remediating after the fact adds cost and processing steps, so getting the microbial load down at the drying step is the better place to solve it.
4. The five, side by side
| Cost | Control | Scale | Wet-season viable | Best use | |
|---|---|---|---|---|---|
| 1. Open-eave barn | near zero | none | large | no | dry-season harvests |
| 2. Sealed room, consumer dehumidifier | ~5,000 THB/unit | low–medium | batch water load within the units’ real-world L/day | yes, if sealed and plumbed | personal grow |
| 3. Sealed room, A/C + dehumidifier | A/C + commercial dehumidifier (local quotes) | medium–high | room-scale | yes | small commercial |
| 4. Small chamber, water-activity control | medium per unit | highest | small batches | yes | premium flower, small batch |
| 5. Hot air, 75 °C | low–medium | n/a | fast, high throughput | yes | extraction biomass only |
5. The five things to get right regardless of setup
- Plumb every drain. A full tank at 3 a.m. hands the room back to ambient at the worst hour.
- Measure the room, not the appliance. Use an independent, calibrated hygrometer placed among the hanging material and away from the dehumidifier’s discharge. The unit’s built-in sensor reads conditions at the machine, not inside the crop.
- Space the material. Every high-humidity thread converges on this: hang individual branches with space between them, not crowded bundles. Crowding creates a saturated microclimate inside the mass, whatever the room reads.
- Size for the peak, not the average. Your entire harvest arrives on one day, and the moisture load is highest in the first days of the dry.
- Budget the dry room separately from the grow room. It is a different problem with a bigger moisture load at harvest, and it is not somewhere to economise after spending on lights.
What is your actual measured room humidity through a wet-season dry, and with what equipment in what volume? Not the target, the reading. Everything above is arithmetic plus other people’s reports. What this region genuinely lacks is a set of measured curves from real Thai dry rooms. If you have logged one, it is worth more than this article.
Sources
- University of Vermont Extension, “Drying and curing herbs and flowers, hops, hemp and everything else”: Drying and Curing Herbs and Flowers (Hops, Hemp, and Everything Else!) – UVM Extension Ag Engineering
- Quest 70 manufacturer product page (ratings, voltage, discontinued notice): Quest 70 industrial dehumidifier | Quest Climate
- Baek Y., Grab H., Chen C. “Postharvest Drying and Curing Affect Cannabinoid Contents and Microbial Levels in Industrial Hemp (Cannabis sativa L.).” Plants 2025; 14(3):414. https://doi.org/10.3390/plants14030414
- ASEAN NOW, “Is it possible to dry buds outside in Thailand?”: https://aseannow.com/topic/1280372-is-it-possible-to-dry-buds-outside-in-thailand/
- ASEAN NOW, “Dehumidifier for drying”: https://aseannow.com/topic/1275085-dehumidifier-for-drying/
- THCFarmer, “How do you dry in high humidity area?”: https://www.thcfarmer.com/threads/how-do-you-dry-in-high-humidity-area.140243/
Related reading on this forum: topics 1363, 245, 1323 and 324.
This article is technical horticultural information for readers operating legally in their jurisdiction. Cannabis is regulated differently in every country. In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568. It may be dispensed only against a PT 33 prescription from an authorised practitioner, online sale and advertising of flower are not permitted, and recreational use is not permitted. Cultivation, extraction and sale require the relevant licences. The Cannabis Control Act is still a draft: the Cabinet approved it on 22 September 2026 and sent it to the House. Nothing here is legal advice.