Why is humidity control so important for industrial hemp suitable for medical use?

Hemp needs different humidity at each growth stage: typically 65–80% RH for seedlings, 55–70% in the vegetative stage and 40–60% during flowering. The inside of dense inflorescences is more humid than the room air; Botrytis (grey mould) develops in this microclimate when relative humidity stays above 85–90% for long periods and surfaces are wet. After harvest, the product must be dried at a controlled rate and brought below a water activity of 0.65. In production for medical use, a batch that fails its microbiological quality requirements cannot be used.

What are the target conditions for drying and curing hemp?

Drying typically takes place at 15–21 °C and 55–65% relative humidity over about 7–14 days; the dew point of these conditions is +6…+14 °C (+10.1 °C at 18 °C / 60%). The product is then cured in closed containers at 18–22 °C and 58–62% RH for 2–8 weeks. The goal is for the dry flower to settle within the 0.55–0.65 water activity range of ASTM D8197 and to meet the maximum 12.0% loss-on-drying limit of European Pharmacopoeia monograph 3028. Drying too fast causes uneven drying and loss of volatile terpenes; drying too slowly increases mould risk.

Which dehumidification technology is used in hemp facilities?

The choice is decided by the room's target dew point and temperature. Condensing (mechanical) dehumidifiers are efficient in seedling, vegetative and flowering rooms where the dew point is +10 °C or higher. Between +5 and +10 °C a condensing unit still works but loses capacity to defrost, so an energy comparison with a silica gel rotor or hybrid system is made. For dew points below +5 °C and for rooms permanently below 15 °C, a silica gel rotor unit is preferred. A drying room at 15–21 °C is usually served by a condensing unit, while at around 15 °C and below a rotor or hybrid system is evaluated.

What is VPD and how is it used in hemp cultivation?

VPD (vapour pressure deficit) is the difference in water vapour pressure between the leaf surface and the surrounding air. Typical ranges are 0.4–0.8 kPa for seedlings and cuttings, 0.8–1.2 kPa in the vegetative stage and 1.0–1.6 kPa during flowering. For example, in a room at 25 °C / 60% RH with a leaf at 23 °C, VPD ≈ 0.91 kPa. VPD is meaningful for the living plant; when drying the harvested product, relative humidity, dew point and water activity are monitored instead.

Which regulation governs hemp cultivation in Türkiye?

Hemp cultivation is governed by the Regulation on Hemp Cultivation and Control published in the Official Gazette No. 33154 of 31 January 2026, which repealed the earlier 2016 regulation. Cultivation requires a permit. For medical and health products, applications are handled through the Turkish Grain Board (TMO), the permit is issued by the Ministry of Agriculture and Forestry, and production takes place in enclosed, climate-controlled, high-security areas.

What does NKT offer for hemp cultivation and drying facilities?

NKT – Nem Kontrol Teknolojileri supplies TFT (Tecnofrigo Tuscany, Italy) condensing and silica gel rotor dehumidifiers and Neptronic (Canada) resistive steam humidifiers, and provides equipment selection support based on each room's target dew point and temperature, as well as technical service and spare parts. Humidity, temperature and dew point can be monitored through the NKT – Pro mobile app with the NKT – Climate Track system.

Technical Article52 min read

Industrial Hemp Drying: Comprehensive Technical Guide

Target temperature, relative humidity, dew point and water activity (a_w 0.55–0.65) for drying and curing industrial hemp suitable for medical use; VPD in growing rooms, choosing condensing or silica gel rotor dehumidifiers by dew point, drying load calculation and Türkiye's 2026 regulation.

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Related Glossary Terms

For deeper definitions of the technical concepts in this article, browse the related entries in the NKT Glossary:

Relative Humidity (RH)Moisture Content (Specific Humidity)Moisture Load Dew Point Latent Heat VPD (Vapor Pressure Deficit)Silica Gel Rotor (Desiccant Rotor)Reactivation (Regeneration)Adsorption Defrost Infiltration Capacitive Humidity Sensor Calibration GMP (Good Manufacturing Practice)TCO (Total Cost of Ownership)ACH (Air Changes per Hour)Sorption (Adsorption + Absorption)Water Activity (aw)VFD (Variable Frequency Drive)Design Conditions (Set Point)Resistive Steam Humidifier Humidification Capacity (kg/h)Silica (SiO₂)Filtration (Water Filtration)Humidity Sensor

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