How to use mushroom filter bags
Filter bags are the standard tool in mushroom growing. Their filter lets through the oxygen the mycelium needs – but keeps out mould spores and bacteria.
What filter bags are for
- Straw pellets – pour on boiling water directly in the bag, inoculate, colonise
- Hardwood pellets for Shiitake, king oyster, Lion's Mane & co.
- Log-in-a-bag: boil short pieces of wood in the bag and inoculate them
- Make your own sawdust spawn – for mushroom beds and logs
How a filter bag works
The sealed-in filter has a pore size of 0.2 micrometres. Mould spores and bacteria can't reach your substrate, but the oxygen the mycelium needs can. Because the bags withstand higher temperatures, you can mix pellets and boiling water directly in the bag.
Step by step (example: pellets)
1. Fill
Put the pellets into the bag, e.g. 0.5 kg straw pellets. Always pull the bag apart from the outside and don't touch the inside.
2. Add water
Add twice the amount of boiling water (1 litre per 0.5 kg pellets). Wear protective gloves! Hold the top closed and mix until all pellets have broken down.
3. Cool
Fold over the top and stand the bag on the fold so no air gets in. Leave to cool for 12–24 hours.
4. Inoculate and close
Add spawn (approx. 10 % of the substrate weight). Close the bag above the filter with a cable tie or clip, leaving as much air as possible above the substrate. Shake well.
5. Colonise and fruit
Let it colonise at 20–24 °C. Once the substrate is white, cut crosses into the plastic and let the mushrooms fruit.
M or L?
Both sizes work the same way. Size M suits smaller amounts of substrate at home, L larger batches and pieces of wood. Both come in packs of 10, 50 and 100.
FAQ about filter bags
Where do I close the bag?
Always above the filter, otherwise no gas exchange can take place.
Can I pour boiling water straight in?
Yes, the bags withstand higher temperatures. Still wear protective gloves.
Can I reuse filter bags?
For clean results we recommend using each bag only once.
Do I really need filter bags for straw pellets?
Not necessarily – straw pellets also work in simple plastic bags. For hardwood pellets, however, filter bags are a must.
No growth, or only weak growth?
Have a look at our FAQ or get in touch via our contact form – ideally with a photo. We are happy to help.
Want more?
Reorder directly from us, discover more mushroom species or learn how to grow mushrooms yourself in one of our courses.
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