Curing Cannabis in Jars: How to Nail the 58% vs 62% Humidity Question (2026 Guide)

Quick Answer

Quick answer: Cure cannabis in sealed glass jars at 58 to 62 percent relative humidity and 60 to 70 degrees Fahrenheit. Use 62 percent for most flower and drop to 58 percent for dense or resin-heavy buds. Treat 65 percent as a hard ceiling. That is the top of the ASTM D8197 range for dry flower and the point where mold risk stops being theoretical.

Most people rush this part. They dry their flower for a few days, stuff it in a bag, and wonder why it smells like grass clippings and burns harsh three weeks later. The cure is where good flower either turns great or quietly falls apart, and the whole thing comes down to one number you can actually control: humidity.

I have ruined cures. I have also nailed them. The difference was never luck. It was holding the jar at the right relative humidity (RH) long enough for the plant to finish what it started. This guide walks through the exact RH targets, the day by day timeline, the gear that holds your numbers steady, and how to read a cure that is heading sideways before it costs you the whole jar.

Why Humidity Decides Everything About Your Cure

Curing is a slow, controlled drawdown of moisture combined with the breakdown of leftover chlorophyll, sugars, and starches inside the flower. Drying gets the bud to roughly the right water content. Curing finishes the chemistry. If the air inside the jar is too wet, microbes and mold get comfortable. Too dry, and the terpenes that carry flavor and aroma flash off and never come back.

The target window is narrow on purpose. Hold the jar between 58 and 62 percent RH and you give the enzymes time to work while keeping mold starved of the moisture it needs. Miss the window in either direction and you are no longer curing. You are either rotting or stale-drying.

What curing actually does to flower

During a proper cure, residual chlorophyll continues to degrade, which is why harsh, hay-like notes fade over two to four weeks. Sugars and starches break down further, which smooths the smoke. Terpenes redistribute and stabilize. None of this happens in a paper bag on a shelf. It needs a sealed environment with enough trapped moisture to keep the process alive but not enough to invite trouble.

A finished cure smells louder, tastes cleaner, and burns to a light gray ash instead of a black, crackly mess. That payoff takes a minimum of two weeks and keeps improving for two months.

The 58 versus 62 percent debate in one paragraph

Here is the short version. 62 percent RH is the safe default for most flower because it keeps buds pliable, preserves terpenes, and resists mold for the majority of strains and home setups. 58 percent is the move when you are working with very dense, trichome-heavy buds that hold moisture deep inside, or when you live somewhere humid and want a safety margin against mold. Below 55 percent the flower dries out and the smoke gets scratchy. Above 65 percent you are gambling with mold. Everything else is fine tuning.

What happens when you ignore humidity

Skip humidity control and you get one of two failures. The wet failure shows up as a sharp ammonia smell within the first week, which is anaerobic bacteria breaking down the plant in a jar with no airflow. The dry failure is sneakier. The flower looks fine but crumbles to dust, the aroma is flat, and the smoke bites the back of your throat. Both are preventable with a five dollar humidity pack and a habit of checking the jar.

The Curing Timeline, Day by Day

A cure is not a set-it-and-forget-it process for the first two weeks. It needs attention on a schedule. After that it coasts. Here is the timeline I follow, and the reasoning behind each phase.

Days 1 to 3: the sweat

When freshly dried flower goes into a sealed jar, the outside of the bud is drier than the inside. Within hours, moisture migrates outward and the RH inside the jar climbs. This is the sweat. Check your hygrometer a few hours after sealing. If it reads above 65 percent, the flower went in too wet and you need to leave the lid off for an hour or two, then reseal.

During these first three days I open each jar once or twice a day for a few minutes. The bud should feel slightly springy, not wet, not crunchy. If a stem snaps cleanly it is on the dry side. If it only bends, you have moisture to manage.

Days 4 to 14: the daily burp

Burping is the core ritual of curing. Once a day, open each jar for two to five minutes to vent the humid air and swap in fresh, drier air. This pulls moisture out gradually and prevents the stagnant, anaerobic conditions that breed that ammonia stink.

Two weeks of daily burping is the standard. I set a phone reminder for the same time each evening so I do not skip a night. Watch the hygrometer trend over these days. You want the resealed RH to settle closer to 60 to 62 percent and stay there a little longer each time. When the number stops spiking back up after you reseal, the worst of the moisture is gone.

Weeks 2 to 8: the slow cure

After roughly 14 days of stable readings, you can stop daily burping and switch to checking the jars once or twice a week. This is where patience pays. The flavor at week two is good. At week four it is noticeably better. By week six to eight the harshness is gone and the terpene profile is as loud as it will get. Some growers cure prized batches for three months or longer.

At this stage a two-way humidity pack does most of the work, holding the jar steady so you can mostly leave it alone.

The bend test before you ever seal a jar

Before flower goes into a jar for curing, it needs to pass the bend test, or you are setting up a wet failure from day one. Take a small branch and bend it. A stem that is ready to jar will bend and then snap with a soft crack, not a clean break and not a limp fold. If the stem only folds without snapping, the flower is still too wet for a sealed jar and needs another day or two of drying on a rack. If it snaps instantly and the buds crumble, you dried too far and should jar right away to stop further moisture loss. I learned this the expensive way, jarring a batch that felt dry on the outside but folded at the stem. Three days later every jar reeked of ammonia. Now I bend three or four stems from different parts of the harvest before a single jar gets sealed.

How to know when the cure is done

There is no exact finish line, but there are signals. The flower holds a steady RH without spiking after you reseal. The aroma is rich and consistent across the jar. A bud bends and the small stems inside snap rather than fold. The smoke is smooth and the ash is pale gray. Once you hit that point, the cure has done its job and you are now in long term storage mode, which follows the same humidity rules.

Picking Your Target: 58 versus 62 Percent RH

The 58 to 62 percent range is not arbitrary. It is the band where the plant chemistry continues, mold cannot establish, and the smoke stays smooth. Choosing your exact target depends on your flower, your climate, and your goals.

When 62 percent is the right call

Reach for 62 percent RH for the majority of flower, especially looser, fluffier buds and anything you plan to use within a few months. At 62 percent the bud stays pliable, rolls well, and the terpenes are fully preserved. New to curing? Start here. It is the most forgiving target and the one that keeps flavor at its peak.

When to drop to 58 percent

Switch to 58 percent for dense, compact, resin-soaked buds that trap moisture deep in the core. Those buds can read 62 percent on the surface while still being wetter inside, which is a mold risk over long storage. 58 percent gives a safety margin. It is also the smarter target if you live in a humid region, if you are storing for six months or longer, or if you have ever had a jar go moldy. The flavor tradeoff is minor and the protection is real.

The 55 percent floor and 65 percent ceiling

Treat 55 percent as the bottom and 65 percent as the top. Below 55 percent, terpenes evaporate fast and the smoke turns harsh and scratchy within weeks. Above 65 percent, you are in active mold territory, and a single moldy jar can mean tossing the whole batch. Staying inside this floor and ceiling matters more than hitting any single number perfectly.

How temperature changes the math

Humidity and temperature are linked. Store cured jars at 60 to 70 degrees Fahrenheit. Warmer than 77 degrees and you accelerate terpene loss and create conditions friendlier to mold and even mildew. Cold is not a fix either. A fridge cycles humidity every time the compressor runs, and a freezer makes brittle trichomes snap off the bud. A cool, dark cabinet at room temperature beats both. Light is the other silent killer, since UV degrades cannabinoids, which is why amber or opaque jars and a dark shelf protect your work.

A quick reference by climate

Your local weather shifts the target. In a dry climate, say the high desert at 20 to 30 percent ambient RH, lean toward 62 percent packs and check jars often, because the dry air outside pulls moisture out fast every time you open a lid. In a humid climate, like the Gulf Coast in summer at 70 percent or more ambient, default to 58 percent packs and burp in a room with a dehumidifier or air conditioning running so you are not venting wet air back into the jar. If your home swings between seasons, store cured jars in an interior closet rather than a garage or attic where temperature and humidity spike. The packs buffer a lot, but they last longer and work better when the room is not fighting them.

The 65 Percent Line: What Actually Happens Above It

65 percent is not a number someone picked for a forum post. It is the published ceiling in ASTM D8197, the standard specification for keeping dry cannabis flower between 0.55 and 0.65 water activity, and it is written into state law. Colorado's Marijuana Enforcement Division set 0.65 aw as the hard upper limit for flower, shake, kief, and trim in a rule effective July 1, 2021. Licensed product testing above that number does not reach a shelf. Your jar should be held to the same line.

Water activity and jar RH are the same number

Water activity (aw) measures the free, unbound water available to microbes on a 0 to 1 scale. Seal flower in a jar, let it equilibrate, and the air above it settles at a relative humidity equal to the water activity times 100. A batch at 0.62 aw reads 62 percent on your hygrometer. That is worth sitting with, because it means the five dollar sensor in your jar is tracking the same property a lab measures with a several thousand dollar instrument under ASTM D8196.

The distinction that trips people up is moisture content versus water activity. Two jars can both sit at 11 percent moisture by weight and behave completely differently, because mold does not eat total water, it eats free water. Your hygrometer reads free water. Trust the stabilized number over how the bud feels between your fingers, because dense flower feels dry on the surface at readings that are not.

What starts growing above 65 percent, and how fast

Flower held inside the 0.55 to 0.65 aw band is considered shelf stable and will not support bacteria, mold, or yeast. Past that ceiling the margin disappears in stages rather than all at once. Common spoilage molds and yeasts begin growing around 0.70 aw, which is 70 percent RH in the jar. Pathogenic bacteria need roughly 0.87 aw, far past anything a curing jar reaches. So the 65 to 70 percent band is not instant mold. It is the buffer between cannot grow and will grow, and it is a five point buffer that a warm room, one under-dried bud, or a hygrometer reading three points low can erase without warning.

Practical timeline once you are past 70 percent: a jar at room temperature can show visible growth in three to seven days, and a jar sitting at 75 percent or higher can do it in about 48 hours. Colonies establish before anything is visible. By the time you can see white fuzz on a bud, the spore load through the rest of the jar is already high, which is why the salvage advice below is to discard rather than pick around the damage.

Temperature moves the line against you

A jar at 65 percent RH in a 65 degree closet and the same jar at 65 percent in an 80 degree garage read identically and are not the same risk. Mold metabolism climbs with warmth, so the same borderline humidity converts to visible growth much faster at the top of the range. This is the real argument for the 60 to 70 degree storage window. Heat alone does not spoil flower. Heat turns a marginal humidity reading into an active problem. If you cannot control the room, control the humidity harder and target 58 percent rather than 62.

Your jar reads 66 percent or higher. Do this.

Open it. Venting a too-wet jar is always the first move and it costs nothing. Then work the list in order.

1. Leave the lid off one to two hours in a room at or below 55 percent ambient RH, reseal, and watch the rebound. A jar that climbs straight back above 65 percent has more moisture in the bud cores than a single vent can pull out.
2. If the rebound is stubborn, spread the buds in a single layer on a clean non-porous surface for 30 to 60 minutes. Skip paper towels and cardboard, which shed fibers into sticky flower.
3. Swap in a 58 percent two-way pack rather than a 62 percent one for this batch. A 62 percent pack in a 67 percent jar will absorb, but it pulls toward a target only five points down. The lower rating works faster, and speed is the whole point here.
4. Go back to burping two or three times a day until the resealed reading holds under 62 percent for three consecutive days.
5. Inspect at every burp under bright direct light, ideally with a loupe. That is how you separate the sparkle of trichomes from the dull, matte, web-like look of early growth.

What not to do matters just as much. Do not add rice, bread, citrus peel, or lettuce to the jar. Those are old forum fixes that swing humidity unpredictably and introduce their own microbes to a container you are trying to keep clean. Do not freeze a jar to stop mold, because freezing pauses growth without killing spores and makes trichomes brittle enough to shatter off the bud. And do not drop in a lower-rated pack and walk away, since a two-way pack is a buffer with finite capacity, not a dehumidifier. If the flower is genuinely too wet, the pack saturates and stops helping right when you need it. The same free-water logic drives concentrate shelf life, which we break down in our guide to whether dabs go bad.

The Gear That Holds Your Numbers

You cannot manage what you cannot measure, and you cannot hold a target without the right container. None of this gear is expensive. It just has to be the right kind.

Glass jars versus plastic versus mason jars

Glass is the standard for a reason. It is non-porous, airtight with a good seal, does not leach anything into the flower, and does not hold odors between batches. Wide-mouth glass jars make it easy to get buds in and out without crushing them. Plastic is a poor choice for curing because it can carry a static charge that strips trichomes, and cheaper plastics can off-gas. Standard mason jars work, but the clear glass lets in light, so keep them in a dark cabinet or choose tinted glass. For both flower and concentrates, our team stocks sealable options in the storage containers collection sized from small personal jars up to larger batch sizes.

Two-way humidity packs

A two-way humidity pack is the single best upgrade for a hands-off cure. Brands like Boveda and Integra both make packs in 62 percent and 58 percent versions. The pack absorbs moisture when the jar is too wet and releases it when too dry, holding your target automatically. Match the pack rating to your goal, drop one in each jar, and replace it when it goes stiff, usually every two to four months. Size the pack to the jar as well, since an 8 gram pack is built for a quart and will struggle in a gallon container. Our full humidity gear guide covers pack sizing and replacement timing in more detail. During the active burping phase the pack works alongside your daily venting. After that, it carries the load.

Hygrometers worth trusting

A small digital hygrometer that sits inside the jar takes the guesswork out of curing. The cheap ones drift over time, so calibrate with a salt test now and then, and replace any that read more than a few points off. I keep one in every jar during the first two weeks because the trend it shows me, not the single reading, is what tells me how the cure is moving. Once jars are stable I rotate hygrometers between them.

Calibrating a hygrometer with the salt test

You do not need lab gear to check a hygrometer, just table salt and a bottle cap. Put about a teaspoon of salt in a small cap, add a few drops of water to make a damp slurry that is not soupy, then seal the cap and the hygrometer together in a zip bag or sealed jar. Leave it six hours. A correctly reading hygrometer will land on 75 percent RH, because a saturated salt solution holds exactly that at room temperature. If yours reads 72, it runs three points low, so add three to every future reading. I check mine every couple of months, and the ones that drift more than four or five points get tossed. A hygrometer you cannot trust is worse than none, because it makes you confident about the wrong number.

Jar fill: why 70 to 75 percent is the target

Fill curing jars to 70 to 75 percent of capacity and leave the remaining quarter as headspace. That gap is not wasted room. It is the air volume that lets moisture migrate out of the bud cores and get carried off when you burp, and it gives buds space to tumble and redistribute instead of compacting at the bottom.

Missing the target in either direction causes real problems. Below about 60 percent full, the jar holds more air than flower. That extra oxygen oxidizes cannabinoids, the larger air mass swings humidity harder every time the lid comes off, and the volume outruns a humidity pack, which is rated for a specific container size. Above about 80 percent full, buds press against each other and the glass, trichomes shear off, and the interior of the pile never exchanges air during a burp, which is exactly how you end up with a wet bottom and a dry top in the same jar.

In amounts you can actually measure: a wide-mouth quart jar holds roughly an ounce of well-trimmed flower at the right fill, and a pint jar holds about a half ounce. If a harvest leaves you an awkward quantity, step down to a smaller jar rather than running a large one partly filled. Right-sizing the container costs a few dollars and is cheaper than what you lose to a jar that is mostly air.

Troubleshooting a Cure Gone Wrong

Most failed cures send a warning before they are lost. Learn the signals and you can usually save the batch.

Ammonia smell means too wet

A sharp, urine-like ammonia note when you open a jar is the clearest danger sign. It means anaerobic bacteria are breaking down flower that went in too wet and was not burped enough. Act immediately. Leave the lid off for several hours to vent, increase burping to two or three times a day, and consider laying the buds on a clean surface for an hour to shed surface moisture before resealing. Caught early, the flower recovers. Ignored, it is gone.

Hay or grass smell means over-dried

A flat, hay-like or fresh-cut-grass smell points to over-drying or a cure that stalled because the flower lost moisture too fast. The chlorophyll never got the moist conditions it needed to fully break down. Adding a 62 percent humidity pack can sometimes rehydrate the flower enough to restart a partial cure, though terpenes lost to over-drying do not come back. Prevention beats rescue here: do not let your initial dry run too long or too hot.

Uneven moisture and how to fix it

Sometimes one jar reads 64 percent while another reads 57 percent, or buds at the bottom feel wetter than the top. Gently rotate and redistribute the flower each time you burp so moisture equalizes. If a single bud is noticeably wetter, pull it and dry it separately rather than letting it pull the whole jar up. Consistent burping and the occasional shuffle keep a jar uniform.

Mold: spotting it and cutting losses

Mold looks like white fuzzy patches, gray spots, or a powdery coating, and it is different from the sparkle of trichomes. If you find it, do not try to salvage that flower. Smoking moldy cannabis is a real health risk, especially for anyone with a compromised immune system. Remove and discard affected buds, inspect the rest of the jar closely under good light, and if the contamination is widespread, cut your losses on the batch. Then lower your target to 58 percent and tighten your burping next time.

Storing Concentrates by the Same Rules

The humidity logic that protects flower also protects the things many of us actually care most about. Concentrates degrade with the same enemies: heat, light, air, and the wrong moisture level.

Why concentrates want it drier and cooler

Concentrates do not need the 62 percent moisture band that flower does. They want it dry, dark, and cool. Excess humidity can make some extracts gummy or speed the breakdown of terpenes and cannabinoids. The shared rule across flower and concentrate is the same: airtight container, out of light, at a stable cool room temperature. For long-term concentrate storage, the breakdown of why glass beats other materials is covered in our notes on concentrate storage, and the airtight options in the concentrate containers collection are sized for everything from a gram to a stockpile.

Jars, not bags, for the long haul

Bags are fine for a quick stash run, but they are a poor long-term home for either flower or concentrate. They let in air every time you open them, hold odors, and offer no humidity stability. A sealed glass jar with the right humidity pack does in one step what a bag never will. If you are putting in the work to cure flower properly, finishing it in the right container is the part that keeps that work from unraveling on the shelf.

The Short Version

Cure in airtight glass at 58 to 62 percent RH and 60 to 70 degrees Fahrenheit. Default to 62 percent, drop to 58 percent for dense buds, humid climates, or long storage. Burp daily for two weeks, then weekly, and let a two-way humidity pack hold the number for you. Fill jars 70 to 75 percent full. Watch for ammonia (too wet) and hay smell (too dry). Treat 65 percent RH as a ceiling you do not cross, because that is where the standards stop calling flower shelf stable. Hit those marks and the flower you worked for tastes the way it should, two months from now and beyond.