How do I know my flower is dry enough?

By Curtis Olson — retired software developer, home grower, and the builder of the device this site is about. More about me and why I built it. · Last reviewed 2026-10-19

The short answer

Flower is dry when its moisture content is right, not when a calendar says so. The published target for smokable flower is 8–13% moisture by weight, which puts it under the 0.65 water-activity line that several state regulators (Colorado, Washington, California) treat as the safety threshold — water activity being how much of the water left in the bud is still loose enough for mold and bacteria to use. Hang-drying typically takes 5–7 days to get there — but “typically” is doing real work in that sentence. Bigger, denser buds take longer; a dry room running at the wet or cold end of its band takes longer. The days are an estimate. The moisture is the endpoint.

Why the target is a range, and what sits at each edge

The number food scientists actually care about is that water-activity figure (aW) rather than the moisture percentage, because it is the part of the water that is loose enough for microbes to use. In cannabis the two line up at roughly 14% moisture to 0.65 aW, which is why the smokable-flower target stops just under it. Below about 0.6 aW, nothing much can grow at all — that’s the spoilage-safety edge of the range. The chapter is equally frank about the other direction: drying too fast or too far costs quality, which is why it doesn’t just say “drier is safer, keep going.”

Labs measure aW directly, but the meters run four figures, so at home you are estimating — by weight loss, by feel, by the usual stem-snap folklore, or by a hygrometer sealed in a jar with the flower (below), which is the closest a home grower gets to the measured number. That’s fine as long as you know that’s what you’re doing: estimating a measured quantity, not counting down a timer.

The outside is crisp and the inside is still sticky

This is the state most growers are in when they ask whether it is time for jars: the sugar leaves are dry and brittle and the buds still feel dense and tacky. Both are true at once because flower dries from the outside in. The thin leaves give up their water in days; the middle of a dense bud is still handing its water outward. Feel is reading the surface, and the endpoint is the whole bud.

There is a cheap way to read the whole bud, and it follows from what water activity is. Seal some flower in a jar with a small hygrometer and wait. The air in the jar settles to a humidity set by the flower, and that settled reading, divided by 100, is the water activity: a jar that holds at 62 % is flower at about 0.62. That is the same number as the 0.65 line above, read with a ten-dollar instrument instead of a lab meter.

Three cautions, so the number is not trusted further than it deserves. Give it time: the reading climbs as the damp middle of the bud catches up with the dry outside, so read it once it has stopped moving, not ten minutes after you close the lid. Cheap hygrometers are commonly off by a few points either way, so treat 0.65 as a line to sit clearly under, not one to land on. And if the jar settles above it, the flower is not ready to stay sealed: take it out and keep drying. The jar method is growers’ practice, not something the chapter below tested; the arithmetic behind it is just the definition of water activity.

Drying room or drying closet: the conditions with actual published backing

The same chapter gives the dry room itself concrete numbers: air temperature 18–21 °C (about 64–70 °F), relative humidity 45–60%, darkness throughout, and generous air exchange. Those are the bands we would hold a dry space to, and they are cooler and wetter than a lot of grow-room folklore suggests — the point of a slow dry is to be slow.

Most home growers are not drying in a room at all but in a closet or a spare tent, and the bands are the same. A small closed space is harder to hold, not easier: a closet full of fresh plants raises its own humidity fast, and one fan or one open door swings it. So in a drying closet, hang the plants loosely, move air around them rather than straight at them, and read the humidity where the flower hangs, not by the door.

And here is the honest caveat, which comes from the chapter itself rather than from us: even the field’s reference text says the optimal drying setpoints have yet to be established experimentally. The bands above are the best published guidance that exists, offered by authors who are candid that they’re describing good practice, not a solved problem. When a source admits the limit of its own evidence, we would trust it more, not less.

What humidity should I dry at, and what if the room will not hold it? “60/60” is a shorthand

The rule of thumb growers trade — 60 °F and 60 % humidity — sits at the damp edge of the published band above and a few degrees below its cool end, and that is why it works when it works. But it is a shorthand, not a law, and the thing it is standing in for is the pull the air exerts on the flower: how hard the room is drawing water out. That pull is set by temperature and humidity together, the same vapour-pressure-deficit idea that governs a living leaf. 60/60 names one point that gives a gentle pull. 65 °F at 55 % gives a very similar pull; 70 °F at 60 % gives a harder one, which dries faster and rougher; 60 °F at 65 % gives a softer one, which dries slower and closer to the mold edge.

So when a room cannot hit 60/60 exactly — and most home dry spaces cannot — the question is not “how far off am I?” but “is the pull about right?” A degree or two warmer with a few points more humidity lands in the same place. What does not land in the same place is drifting warm and dry together (fast, harsh) or cool and wet together (slow, risky). The endpoint is still the moisture content; the pull just decides how many days it takes to get there and how much of the aroma survives the trip.

There is now a direct test of what the gentle pull buys. A 2026 study dried one cultivar three ways. Buds held at 20 °C (68 °F), 60 % humidity for four days and 55 % after that, took six to seven days to reach about 14 % moisture, and kept as much essential oil as fresh flower: 2.5 %. Freeze-dried buds were done in about 11 hours and lost roughly 40 % of it. A 40 °C oven took 35 hours and shifted the terpene mix toward oxidised compounds. The cannabinoids barely moved under any of the three. It is one cultivar with three samples per method, and the buds were trimmed wet before drying, so whole branches hung up will take longer. But it is a measurement, and it lands inside the published band above, at its damp end.

What about curing?

Here the published record gets genuinely strange: there are no peer-reviewed publications on cannabis curing. None. That sentence comes from the field’s own textbook, not from a skeptic. Every confident claim you have read about what two weeks in a jar does chemically — whatever its merits — is practitioner knowledge, not measured science. Curing may well matter; growers with decades of experience insist it does. But nobody can currently tell you, with data, how long is long enough or what exactly is happening in the jar. Which means any app or device selling you a precise “days until cured” countdown is putting a decimal point on folklore.

Where our device fits, stated narrowly

Croplock treats the dry space as its own room with its own targets — the published bands above, held cool, wet-ish and dark — and where you’ve handed it equipment, it holds the room there and records what it did. What it deliberately does not do is show you a “days until jars” countdown, for the reason this whole page exists: the endpoint is a measured state of the flower, and the call is yours to make.

Sources

• Caplan, D., Matzneller, P. & Gutierrez, C. “Harvest and Post-Harvest.” Ch. 10 in Handbook of Cannabis Production in Controlled Environments (Y. Zheng, ed.), CRC Press, 2022. DOI 10.1201/9781003150442. Moisture and water-activity targets, dry-room bands, typical durations, and both candour statements (setpoints not established; no peer-reviewed curing literature) are from §10.7.
• Grant, C. et al. (2004), on water activity and microbial growth limits, as cited in the chapter above.
• Mallis, E., Koukovinos, N. et al. (2026). Post-harvest drying determines cannabinoid and volatile composition in pharmaceutical cannabis (Cannabis sativa). Journal of Cannabis Research, article in press. DOI 10.1186/s42238-026-00514-9. Drying settings, moisture timeline, essential-oil yields and the cannabinoid comparison are from its methods and results.

More of these at Answers. The device is at croplock.com.

Also read: Bud rot: how humid, for how long? · How should I store flower after the cure? · Can trichome colour tell me when to harvest?