Field Guides

How to store cannabis: keeping flower fresh and locked away

By SŌMA 9 min read Updated

Dried cannabis flower is perishable. After harvest its aroma compounds fade and its THC slowly breaks down, and how it is kept decides how fast. Light, air and warmth speed the change up; the wrong humidity leaves flower prone to breaking up or open to mould.

In New York there is a second job: keeping cannabis away from children and pets. This guide covers both, and its sources are listed at the end.

Start with New York's advice: locked, and in the original package

New York's Office of Cannabis Management (OCM) asks adults to store cannabis locked, out of sight and out of reach of children and pets, and to keep it in its original child-resistant packaging. Its safe-storage card is plain about it: keeping products out of reach is not enough; they should be locked and out of sight. A locked container, or a lockable drawer or filing cabinet, will do.

The original package is also a good place for the flower. New York's packaging rules require a retail package to stay child-resistant for the useful life of the product, to be resealable if it holds more than one serving, and to minimise oxygen exposure and prevent the product's degradation. Its label carries the warnings, the expiration date and the storage conditions to follow. So the first storage habit is the simplest one: close the package properly every time.

The rest of OCM's checklist

  • Keep cannabis apart from everyday food and drink and away from common household areas. OCM singles out infused drinks and gummies, which should not sit in a shared fridge or pantry.
  • Clear up after use: ground flower, crumbs, lighters and matches left out.
  • Ask visitors, grandparents and anyone looking after your child or pet to lock their cannabis away too.
  • Put cannabis waste in a bin with a closed lid, out of reach of children and pets.

If someone takes it by accident

Call the Poison Center at 1-800-222-1222 if you think someone has been accidentally exposed to a cannabis product or has taken too much, and call 911 if the person shows signs of an emergency. In New York City the NYC Poison Center is also on 212-POISONS (212-764-7667).

Light: keep it in the dark

In a two-year study of herbal and resin cannabis and of cannabinoid solutions, exposure to ordinary light (not direct sunlight) was the greatest single cause of cannabinoid loss, most of all for cannabinoids in solution. The same study judged carefully prepared flower reasonably stable for one to two years when kept in the dark at room temperature. A later four-year study found that light changed both how fast THC broke down and how much of it turned into cannabinol (CBN).

In practice: a closed cupboard, drawer or box, not a windowsill or a lit shelf.

Air: keep it closed, and whole

THC oxidises over time, and CBN is its main breakdown product. In the two-year study, air oxidation caused significant losses and, in the dark, raised CBN. The authors concluded that those losses could be reduced by taking care not to damage the resin glands, which they described as acting as “well filled, well closed containers”.

In a one-year laboratory study, ground flower held higher levels of breakdown products than whole flower, especially at 25°C, which the authors suggest may be due to the larger surface area exposed to air. Aroma compounds were measured in one CBD-rich variety: after four months, every ground sample of it had somewhat lower levels of them than the matching whole one. Keep flower whole and grind it just before use.

Warmth: keep it cool

Warmth speeds the change up, though not at every temperature studied: the two-year study found that temperatures up to 20°C made no significant difference. The later studies found losses at room temperature. In the four-year study, samples of six high-potency herbal and resin products kept at 22°C, in light or in darkness, lost THC and gained CBN significantly, and almost all of their THC had broken down after four years; temperature changed how fast that happened. In the one-year study, which kept whole and ground flower in the dark at 25°C, 4°C, −30°C and −80°C, 25°C changed the cannabinoids most, and whole flower at 4°C kept its composition best.

An older four-year study, of dried plant material grown in 1991 and 1993 and kept in closed barrels in the dark at 20–22°C, found a slower pace: THC fell on average by 16.6% of its starting value in the first year and by 41.4% by the fourth, with wide variation between samples. Its authors believe that the higher the THC, the faster it breaks down over the first one or two years. More on what that means for buying in Why freshness matters.

That does not make the family fridge the answer. OCM advises storing cannabis separately from regular food and drink and away from common household areas, and its safe-storage card says infused products should not be kept in a shared fridge or pantry near other food. A locked box in a cool, dark cupboard, away from the oven, radiators and sun, follows the evidence and the advice together.

What about the freezer?

Cold slows the loss of THC. Older work summarised by Ross and ElSohly found THC lost 3.83% a year at −18°C, 5.38% at 4°C and 6.92% at 22°C over two years of storage, and in the four-year study the significant changes reported were in the samples kept at room temperature; the others were kept at 4°C and frozen at −20°C. For aroma compounds the evidence is thinner. In the one-year study, which measured them in one CBD-rich variety after four months, they fell under every condition, and the authors found the two temperatures below −20°C, −30°C and −80°C, the least favourable. No study we read measured aroma compounds at −18°C or −20°C. The freezer also holds food, so OCM's advice to keep cannabis apart from food and drink applies to it as it does to the fridge.

Humidity: between 55% and 65%

The moisture that matters is measured as water activity, which describes how flower in a sealed container sets the humidity of the air inside it. ASTM's standard for dried flower puts the range at 0.55 to 0.65, the same as 55–65% relative humidity in that air: below 0.65 to guard against mould and other microorganisms, above 0.55 so the flower does not break up in handling and storage. New York requires flower to be tested for water activity and moisture content, which OCM describes as indicators for harmful microorganism growth.

If you want to hold that range, the ASTM standard describes keeping flower in a sealed container with salt-based humidity-control sachets designed to hold the air between 55% and 65%. Choose one rated inside that range.

Container: keep the original package closed

This guide used to advise moving flower into a glass jar. In New York, OCM's advice is to keep it in the original package, and the packaging rules already require that package to fully enclose the product, minimise oxygen exposure and prevent degradation, and to be resealable if it holds more than one serving. Close it properly after each use. One review of postharvest handling says flower kept for months in polyester-film bags gradually loses moisture.

Reading the age of what you have

A New York label must give the date of expiration of the unopened product and its proper storage conditions. The rules tie that date to the product left unopened and kept as the label says, and OCM's guide to reading a label makes the same point: cannabis changes when it is exposed to air, so its lab certificate will not be accurate forever, and the expiration date is the check while the package stays unopened. Follow the storage conditions printed on your label.

The label rules do not ask for a harvest or packaging date. Since March 2026, OCM has required a Retail Item ID QR code on each unit a dispensary receives, and since 1 April 2026 a passing test status in Metrc as well; products a shop received before 1 April 2026 may still be sold without one, up to their expiration date. Our guide to the New York cannabis QR code shows how to read the Metrc Retail ID record it opens, as the producer filed it, for the packaged and test dates.

A short checklist

  • Locked, out of sight and out of reach of children and pets, in the original child-resistant package.
  • Closed properly after every use.
  • Dark: a cupboard, drawer or box, not a windowsill or a lit shelf.
  • Cool, away from heat and sun; not in a fridge or freezer shared with food.
  • Whole until you use it; grind just before.
  • If you use a humidity-control sachet, one rated between 55% and 65%.
  • Read the label's expiration date and storage conditions, and the packaged and test dates through the QR code.

Sources

Frequently asked questions

How long does cannabis flower stay good?

There is no single figure. A New York label gives an expiration date, which applies while the package is unopened and kept as the label says. Studies differ on the pace of THC loss: in an older study of plant material kept closed in the dark at 20–22°C, THC fell on average by 16.6% in the first year, with wide variation between samples; in a later study of high-potency herbal and resin products kept at 22°C, almost all of the THC had broken down after four years. In one laboratory study, of one CBD-rich variety, aroma compounds fell faster than the cannabinoids: on average by more than half within four months.

Should I keep cannabis in the fridge or freezer?

Not one shared with food: New York's Office of Cannabis Management advises storing cannabis separately from regular food and drink and away from common household areas. On the evidence alone, cold slows the loss of THC, and in one laboratory study whole flower kept dark at 4°C held its composition best; in the same study aroma compounds fell most at −30°C and −80°C, and we found no study of them at −18°C or −20°C. A locked box in a cool, dark cupboard meets the advice.

What humidity is best for storing cannabis?

ASTM's standard for dried flower sets water activity between 0.55 and 0.65, the same as 55–65% relative humidity in a sealed container: below 0.65 to guard against mould, above 0.55 so the flower does not break up. Humidity-control sachets designed to hold that range can be kept with the flower in a sealed container.

What does New York say about storing cannabis at home?

The Office of Cannabis Management advises keeping cannabis locked, out of sight and out of reach of children and pets, in its original child-resistant packaging, and apart from everyday food and drink. If you think someone has been accidentally exposed, call the Poison Center at 1-800-222-1222, or 911 in an emergency.

Why does the same strain seem weaker or flatter than last time?

Packages sold under one name can differ in grower, batch and phenotype (see Why the same strain can feel different). Age and storage are part of it too: THC breaks down over time, faster with light, air and warmth, and in one study of a CBD-rich variety aroma compounds fell faster than the cannabinoids. The QR code guide shows where to read when each package was packaged and tested.

Corrections

  • We advised moving flower into a glass jar. New York's Office of Cannabis Management advises keeping cannabis in its original child-resistant packaging, locked and out of reach of children and pets; the guide now starts there, with the state's packaging rules.
  • We said glass, unlike plastic, does not carry a static charge that strips resin from the flower, and that plastic bags are fine for a day or two. We found no study supporting either and removed them.
  • We gave 55–62% as a common target humidity and named a brand of humidity pack. The ASTM standard for dried flower sets 0.55–0.65 water activity, which corresponds to 55–65% relative humidity in a sealed container; the guide now says so and names no brand. We also removed the claim that 62% keeps flower springier and 58% gives a smoother draw, which we could not source.
  • We said heat above roughly 25°C encourages mould. We found no source for that figure: the ASTM standard ties mould to moisture (water activity above 0.65). The figure is removed.
  • We called the fridge a trap because it runs humid and invites mould. We found no source for that; a laboratory study found whole flower kept dark at 4°C kept its composition best. The guide now says that, and that OCM advises storing cannabis apart from food and drink.
  • We said freezing makes the resin glands brittle, so they snap off when frozen flower is handled. The only source we found describes resin turning brittle when flower is agitated in ice water for industrial extraction, not flower kept in a home freezer, so the claim is removed. The guide now says what studies found at freezer temperatures, and that OCM's advice to keep cannabis apart from food applies to the freezer too.
  • We said light, especially UV, is the single fastest way to break down cannabinoids. We found no source for light, or UV, being the single fastest cause. A two-year study found ordinary light (not direct sunlight) the greatest single factor in cannabinoid loss, especially in solution; the guide now says what that study found.
  • We said well-stored flower holds most of its aroma and potency for six months to a year, and that badly stored flower can fade within weeks. We could not source either range, and the first is contradicted by a study we cite: aroma compounds were down by more than half on average within four months under every storage condition tested. The answer now gives the label's expiration date and the measured rates.
  • We said a shop's storage habits signal freshness and advised checking the packaging or harvest date. New York's label rules require an expiration date, not a harvest or packaging date; the guide now says where the packaged and test dates can be read.
  • We said flower kept too dry turns harsh and dusty and its terpenes evaporate, that a steady mid-range beats a jar that swings wet and dry, that cool and stable is the goal, and that quality flower is kept in opaque or tinted containers; and, asked why the same strain can feel weaker than last time, that it is often storage and handling rather than the genetics. We found no source for these and removed them. The guide now gives ASTM's humidity range, says what studies found on light and warmth, and answers that packages sold under one name can differ in grower, batch and phenotype as well as in age and storage.
  • We said that in a one-year laboratory study every ground sample had lower levels of aroma compounds than the matching whole one. Those compounds were measured in one CBD-rich variety, after four months, and the differences were small: of the two compounds the authors compared in detail, only one, α-pinene, was slightly lower in ground flower. The guide now says so.