Answer
Hold cannabis flower between 58% and 62% relative humidity at 60 to 70 degrees F. Use an airtight glass jar with a two-way humidity pack rated at 62% RH. Fill the jar to about three-quarters of volume. Track the level with a digital hygrometer. The target water activity range is 0.55 to 0.65 aw.
Cannabis Storage Humidity Too High: Causes and Fixes
Target numbers
- Relative humidity: 58 to 62%
- Water activity: 0.55 to 0.65 aw
- Temperature: 60 to 70 degrees F (15 to 21 degrees C)
- Light: dark
- Container: sealed glass, stored in a cabinet
Why those numbers
Below 55% RH, flower dries out. Terpenes evaporate, trichomes turn brittle, and weight drops. Above 65% RH, water activity passes 0.65 aw. That is the point where mold and bacteria grow on plant material. Aspergillus and Botrytis both need free water. A jar held at 70% RH keeps that water on the surface of the bud.
Containers
Glass jars with a rubber gasket and a clamp lid hold humidity best. Screw-top mason jars work. Plastic bags and thin food containers pass water vapor through the walls, so the level drifts. Fill a jar to about 75% of volume. Leave the rest as air space so vapor can move. Packed jars trap moisture in the center of the flower.
Cannabis Storage Humidity Chart: What RH to Target and Why
Humidity packs
Two-way packs release and absorb water vapor to hold a set RH. Use 62% for storage. Use 58% for flower you plan to grind in the next few weeks. Pack size tracks jar volume. An 8-gram pack covers up to 1 ounce of flower. A 67-gram pack covers up to 1 pound. Replace a pack when it turns rigid and crunchy.
Measure
Digital hygrometers for jars cost under $20. Calibrate each one with a salt test. Put half a cup of table salt and a few drops of water in a sealed bag with the hygrometer. Wait 24 hours. The reading should be 75% RH. Note the difference and adjust your numbers.
Curing
Freshly cut flower sits at 70 to 75% RH. Dry it down to 62% before it goes in a jar. Burp jars for 5 to 10 minutes one time per day during week one. Burp one time every two days during week two. After that, burp one time per week. Stop burping once the RH holds steady at 62%.
Errors to avoid
- Orange peel and bread slices. They push RH past 65% and can carry mold spores.
- Refrigerators. Each trip out of the cold forms condensation on the flower.
- Sunlight and heat. UV light degrades THC and terpenes.
- Overfilling. No air space means no vapor movement.
- One hygrometer for many jars. Jar readings differ.
Warning signs
Ammonia smell: moisture is too high. Hay smell: flower dried too fast. White fuzz or gray patches: mold, discard the batch. Stems that snap: below 55% RH. Recheck each jar every two weeks. A sealed jar at 62% holds for 6 months or more.