HOW TO STORE HEMP FLOWER AND RESIN

The 15 to 20 °C window is the one we give in the FAQ of our product catalogue, and it matches a classic finding: in the 1976 stability study by Fairbairn, Liebmann and Rowan, temperatures up to 20 °C made no significant difference to cannabinoid losses, while light was the single biggest cause of decline. The humidity window comes from ASTM D8197, the industry standard that sets the water activity of dried flower between 0.55 and 0.65.

The 12 month figure assumes the flower stays in its original packaging, somewhere cool, dry and dark. A pouch opened every day on a sunny shelf will lose much of its aroma within weeks, whatever the label says.

Everything that gives a flower its value sits in the glandular trichomes, the tiny resin heads that make the buds sparkle. That is where the plant builds its cannabinoids (CBD, CBG, CBN and the rest) and its terpenes, the aromatic molecules behind each cultivar's signature. After harvest and drying nothing tops that reserve up again. Storage cannot add quality; it can only slow down the loss.

Terpenes go first

Terpenes are volatile, and they are the first thing to fade. A Technion team led by David Meiri (Milay et al., Frontiers in Plant Science, 2020) followed whole flowers for a year at 25 °C, 4 °C, minus 30 °C and minus 80 °C. On average, more than half of the terpenes were gone after four months, while cannabinoids had dropped by roughly 26% after twelve months. Aroma is therefore the most sensitive gauge of how well a batch has been kept.

Not every terpene behaves the same. Small monoterpenes such as myrcene, limonene and pinene escape far more readily than heavier sesquiterpenes like caryophyllene. Ross and ElSohly measured this in 1996 (Journal of Natural Products): after one week of drying and three months of storage, the essential oil yield of fresh buds had fallen by about 55%, and monoterpenes had shrunk from 92% to 62% of the oil. That is why a bright citrus cultivar dulls faster than a peppery, woody one. Our terpene guide covers these aroma families and their volatility in depth.

Cannabinoids oxidise slowly

Cannabinoids are sturdier but not immortal. Oxygen, light and warmth gradually reshape the profile, and the best known marker of ageing is CBN, which builds up as material gets older (see our CBN guide). A well stored flower will still show, months later, a lab profile close to its original sheet.

Whole buds outlast broken ones

A whole bud is its own packaging: bracts and sugar leaves shield part of the trichome layer. In the Technion study, ground samples held fewer terpenes than whole ones and lost them faster. Simple rule: never break a bud up before storing it.

For day to day storage and for stock that keeps moving, 15 to 20 °C is the sweet spot. It is cool enough to slow terpene loss and close enough to room temperature to avoid the traps of cold storage (condensation, brittle trichomes). The exact figure matters less than stability. A cupboard that swings from 14 °C at night to 26 °C in the afternoon makes the container breathe, and each cycle pulls fresh air and moisture in.

Good spots and bad spots

• Good: an inside cupboard, a dresser drawer, a wardrobe in an unheated room, a dry basement.
• Bad: on top of the fridge or oven, next to a radiator, in a car, under a window, in a lit display cabinet.
• Watch out: south facing rooms in summer, lofts, shop floors without air conditioning.

Keeping material for more than a year

Long term studies show that colder storage slows cannabinoid decline further, especially in resin and extracts. An Italian team (Zamengo et al., Forensic Science International, 2019) tracked hash and flower for four years: only freezing at minus 20 °C prevented a significant drop, and refrigeration alone did not manage it over that period. Cold has its own drawbacks, covered in the fridge and freezer section. For flower that needs to stay presentable, 15 to 20 °C remains the benchmark.

Humidity is the most technical variable. People talk about moisture content, but the number that really matters is water activity (aw): how available the water in the material is, on a scale from 0 to 1. In a sealed jar, flower and air reach equilibrium, and the relative humidity of the air (in %) then equals the water activity times 100. A bud at aw 0.60 will hold its jar at roughly 60% RH.

Too humid: the mould line

ASTM D8197 keeps water activity below 0.65 to guard against microbial growth and calls for further drying when it exceeds 0.68. Technical literature puts the practical limit for most moulds and yeasts around 0.70. Between 0.65 and 0.70 only species adapted to dry conditions can grow, but the safety margin has gone.

Too dry: brittle buds

Below 0.55 flower turns crumbly. Trichome heads, the most fragile part, snap off at the slightest knock and end up as dust at the bottom of the jar. Over dried buds also look duller and lose their bouquet sooner. The same ASTM standard sets the 0.55 floor precisely to prevent breakage during handling.

Measure, don't guess

A small digital hygrometer in a test jar costs little and spares you nasty surprises. Leave it in the closed jar for about twelve hours before reading so the air can settle. Professionals use dedicated water activity meters, which are more accurate, plus data loggers that keep a history (see bulk stock).

A two-way humidity pack holds a saturated salt solution inside a membrane that lets moisture in the air pass but keeps the liquid in. If the jar air is too dry, the pack releases moisture; if it is too damp, the pack soaks it up. The result is a fixed relative humidity, printed on the label. It is the simplest way to stay in range without checking the jar every day.

Using humidity packs properly

• Match pack size to container volume using the maker's chart.
• Lay the pack on top or along the side, never crushing the buds.
• Replace it once it turns hard and crystallised: it is spent.
• A pack cannot rescue soaking wet flower. It corrects a few points, not a botched dry.
• Keep packs for flower only. With resin and extracts they are pointless or even harmful.

Single use desiccants such as silica gel work in one direction only: they absorb and never give back. Inside a jar of flower they end up over drying it. They belong in a shipping carton or a stock room, not in direct contact with the product.

Glass: the gold standard

Glass is chemically inert: it releases nothing and absorbs nothing. Amber glass, a pharmacy staple for generations, stops radiation below roughly 450 nanometres, which covers UV. Violet or black glass goes further by filtering visible light too. Still, no jar beats a closed cupboard: total darkness is the safest protection of all.

Why thin plastic and zip bags fall short

Polyethylene and polypropylene films let oxygen creep through and soak up part of the aroma compounds, so the bag ends up smelling of flower while the flower goes flat. Plastic also builds up static, which pulls trichomes onto the walls. A zip bag is fine to carry a sample for a few days. For storage, switch to glass or steel.

Size the jar to the stash

A big jar half full traps a lot of air, and therefore a lot of oxygen. Pick a container only slightly larger than what you keep, fill it loosely so air can move between buds, and favour several small jars over one big one: you only open the one you need.

Resin is already concentrated material: trichomes gathered together, often pressed, with far less surface exposed to air than a flower. That explains its good shelf life. Lindholst's 2010 work on resin and extracts kept at minus 20 °C found stable cannabinoid levels over four years. Resin is still sensitive to warmth, which softens it, and to air, which oxidises the surface and darkens it.

Match storage to texture

• Pressed slabs and blocks: they handle vacuum sealing well, since there is nothing left to crush.
• Sieved hash, pollen, sandy textures: a glass jar filled to the brim, without compression.
• Creamy, oily resin: baking paper first, then an airtight jar in a cool spot so it neither runs nor sticks.

Parchment, the quiet ally

Parchment paper (baking paper, ideally unbleached) does not stick to resin and protects its surface from contact. Wrap each piece on its own, then place it in a jar or vacuum bag. Avoid foil in direct contact and cling film, which clings and traps aroma.

Cold for the very long haul

To keep resin beyond a year, the fridge and then the freezer become worthwhile. Grafström's Swedish study found no measurable change over four years in slabs stored at minus 20 °C in the dark. The conditions: a truly airtight wrap and letting the package warm up before opening (see below). To compare resin styles, see our complete CBD guide and our CBG guide.

Extracts (crumble, shatter, badder, wax and other textures) are the densest products in cannabinoids and terpenes, and also the least stable. In the Technion study, extracts degraded faster than flowers kept under the same conditions. Three threats dominate: oxidation, terpene loss and texture changes.

Glass or silicone?

Food grade silicone is convenient because nothing sticks to it, but it is gas permeable: fine for a few days, a poor choice for months. A glass jar with an airtight lid, lined with a square of parchment if needed, is the long term reference.

Cold, without shocks

Extracts keep better in the fridge than at room temperature, and in the freezer for the very long term. What harms them is fluctuation: each cold to warm swing creates condensation and can change the texture. Take the jar out, let it reach room temperature closed, take what you need, then put it back quickly.

Preventing crystallisation

Some extracts start to "sugar up": crystals form and the texture turns grainy. This nucleation is encouraged by temperature swings, impurities, dust and repeated handling. A clean jar, steady cold and few openings keep it in check. Crystallisation changes appearance, not the composition of the batch.

Spotting oxidation

A light extract turning deep amber, a dulling surface or a fading bouquet all point to advanced oxidation. Filling the jar to the top and opening it as rarely as possible are the two best defences.

The fridge

A fridge slows oxidation, which mainly helps resin and extracts. For flower it brings two problems: the door opens constantly, so temperature swings, and humid air seeps into any container that is not fully sealed. If you use one, pick the back of a shelf, never the door, and an airtight glass jar.

The freezer

Nothing slows chemistry like a freezer, as the four year forensic studies show. But at those temperatures trichome heads turn brittle as glass and snap off at the slightest knock. The Technion study also recorded the steepest terpene drop in flowers stored at minus 80 °C. For flower, freezing only makes sense for very long storage with zero handling until it has warmed up. For resin and extracts, it is an excellent option.

The golden rule of thawing

Never open a cold container. Room moisture would condense straight onto the product. Let the closed jar warm to room temperature (several hours for a large volume) before opening, and avoid refreezing the same batch: split it into portions before it goes in.

The wine cellar

A wine cellar offers what we want: darkness, a steady 12 to 14 °C, no vibration. Its weak point is humidity, set for cork stoppers and often above the target for flower. The fix is to store airtight jars with a 58% or 62% pack inside: the cellar brings stability, the jar keeps its own climate.

Setting up the room

A good stock room is dark, cool and dry: no windows or blacked out ones, air conditioning or at least no sun facing walls, and a dehumidifier if ambient air regularly tops 65%. Shelving stays away from heat sources, and containers stay closed outside order picking. Resellers building a supply line will find our trade terms on the CBD wholesale page.

On the quality side, our batches are lab tested and lot traceability links every container to its reference. To judge material in hand before committing to stock, use our sample request.

Trichomes or mould?

Under a loupe, trichomes look like tiny crystal mushrooms, a stalk with a round head, neat and shiny. Mould forms tangled, matte filaments that bridge several areas like a spider's web. If in doubt, isolate the container, never mix it with another batch and tell your supplier.

Transit packs every storage enemy into a few days: knocks, temperature swings, pressure. Good shipping packaging rests on three layers.

• Primary barrier: vacuum bag for resin, heat sealed opaque barrier pouch or rigid jar for flower, to cut off air and odours.
• Mechanical protection: a rigid carton with snug padding, so buds are neither crushed nor rattled.
• Plain outer box: no mention of contents, a clear label and parcel tracking.

Our parcels leave in discreet, secure packaging with tracking included. On arrival, open the box in a temperate room, let the contents warm up if they travelled in cold weather, check appearance and move everything into your storage containers straight away. Transit times depend on destination and carrier, so simply avoid leaving a parcel in a hot car or a sunny letterbox.