Two things happen to stored flower. The aromatic compounds that give it smell and character evaporate or oxidise, and the resin on the surface slowly converts and dulls. Neither is reversible. Everything about good storage is about slowing those two processes, and all four of the usual culprits — light, heat, oxygen and unstable humidity — speed them up.

A paper bag in a warm kitchen will flatten a fresh batch in a couple of weeks. The same flower in a sealed glass jar in a dark cupboard at room temperature keeps most of its character for several months.

Light: amber or opaque glass is better than clear, and a cupboard is better than a windowsill. Ultraviolet light degrades the surface of the flower quickly, which is why the best-smelling batch you ever bought was probably the one that never sat in direct sun.

Heat: cooler is better, but not cold. A stable 15 to 21°C is the range to aim for. Above about 25°C degradation accelerates, and the top of a fridge or a shelf above a radiator is a bad place for a jar.

Oxygen: fill jars as close to full as is practical and open them as rarely as possible. Every time you open the jar you replace the headspace with fresh oxygen and release the aromatics you were trying to keep.

Humidity: this is the one people ignore. Target roughly 58 to 62% relative humidity in the jar. Drier than that and the flower crumbles and burns hot; damper and you are inviting mould. A two-way humidity pack in the jar holds the range without any guesswork.

A screw-top glass mason jar with a good seal is the standard for a reason: it is inert, airtight and opaque if you want it to be. Plastic tubs are fine for a week and gradually let aromatics through the walls. Vacuum sealing is excellent for long-term storage of amounts you will not touch for months, but it compresses the flower and is impractical for the jar you open daily.

Avoid the fridge for anything you are smoking this month. Every time you open it, condensation forms on cold flower, and repeated moisture swings are worse than a stable cupboard. The freezer only makes sense for long-term storage of sealed, airtight portions, and even then only if you let them come to room temperature before opening.

Grey-white fuzz, a musty smell that does not smell like the flower did before, or a powdery dust when you break a bud open all mean the batch is compromised. Mould produces compounds you do not want to inhale, and no amount of drying or picking at it makes the batch safe. If you are unsure, throw it out — this is the one place where being cautious costs you a jar and nothing else.

The classic cause is flower that went into the jar too damp, or a humidity pack that was added to already-wet flower. If the flower feels damp when you buy it, leave it in the open air in a dark room for a few hours before sealing it up.

Glass jar, roughly 60% humidity, dark cupboard, around 20°C, opened as little as possible. Do that and you will notice the difference on the last gram of the jar as much as the first.