How long do spores stay intact? Age, storage and what "viable" means for microscopy

01Intact, not viable

In cultivation "viable" means able to germinate, which is not something this library deals in. For microscopy the useful question is whether the spore still has its wall, its shape and its pigment, because those are what you examine. A spore can be intact on a slide long after it has ceased to be anything else. That is why old prints in herbarium collections are still studied a century on.

02What ages a specimen

• Heat. The main cause. Weeks at room temperature or a spell in a warm parcel, and the proportion of collapsed, empty walls climbs.
• Light. Ultraviolet breaks down pigment and wall structure. Keep specimens dark.
• Contamination. Bacteria in a poorly filled syringe multiply over time and eventually overwhelm the slide. This is the "went off" syringe, and it was never a clean one.
• Freezing. Ice damages spores in suspension. Never freeze a syringe.

03Syringe versus print

A print, sealed, dry and dark, keeps for years and is the archival format. A syringe, refrigerated, keeps for many months and often much longer, but as a suspension it is more vulnerable to heat and to any contaminant that got in at filling. If you want a line on the shelf for the long term, keep a print of it alongside the syringe.

04Reading age on the slide

A fresh specimen shows full, evenly pigmented spores with clear walls and very little debris. An aged one shows a rising share of empty or collapsed walls, granular contents, and background debris. Bacterial haze means contamination rather than age. Take a slide from every specimen when it arrives; the comparison a year later is the only reliable shelf-life test there is.

05Why the LOT date matters more than a number

A shelf-life figure on a listing tells you nothing about how the syringe was stored before it reached you. The LOT date does. MycoWorld prepares syringes to order in small batches and refrigerates them from filling to dispatch, so the date on your label is recent and the clock starts in your fridge, not in a stockroom.