Making mushroom substrate from straw pellets
Pellet production reaches over 70 °C – so straw pellets are practically sterile and ideal for mushroom growing. With boiling water you have a ready substrate in minutes.
Suitable for
Oyster mushrooms, summer oysters, lemon oysters, pink oysters and king oysters.
What you need
- Organic straw pellets
- boiling water (twice the weight of the pellets, i.e. 1 litre per 0.5 kg)
- spawn (approx. 10 % of the substrate weight)
- mushroom filter bags, plastic bags or tubular foil
- pot with lid, protective gloves, cable ties or clips
Step by step to your substrate
1. Boil water
Bring the required amount of water to the boil. A weight ratio of pellets : water = 1 : 2 (i.e. 0.5 kg pellets to 1 litre of water) usually works well. The finished substrate then has a water content of about 55–65 %.
2. Pour over the pellets
Put the pellets into a pot (only about a quarter full – they swell a lot) or directly into a mushroom filter bag. Pour the boiling water over them. Only work with protective gloves and long sleeves! Most pellets break down within seconds; mix in any remaining ones with a clean spoon.
3. Let it cool
Before inoculating, the substrate must cool below 35 °C. Put the lid on (or fold over the filter bag) and leave it overnight – this takes about 6–8 hours.
4. Inoculate
Add about 10 % of the substrate weight in spawn (approx. 200 g spawn per 2 kg substrate) and mix well with a clean spoon.
5. Fill and close
Fill the mixture into bags up to about 10 cm below the rim and close them as close to the substrate as possible. Close filter bags above the filter. Cut several crosses of about 2 cm into plastic bags straight away – the mushrooms will grow out through them later.
6. Colonise and fruit
Let the bags colonise at 20–24 °C until the substrate is white. For fruiting, they need a cool, shady, damp spot. If the spot is rather dry, mist the openings once or twice a day.
Hygiene tip
Always pull plastic bags apart from the outside and don't touch the inside – fingertips often carry germs that can hamper mushroom growth.
Which spawn goes with it?
- Oyster mushroom grain spawn – robust, fruits cool
- Summer oyster grain spawn – for warm rooms
- Lemon oyster grain spawn – yellow and warmth-loving
- King oyster grain spawn – grows on straw, but more reliably on wood
Troubleshooting
Substrate too wet
If water is standing in the bag, there was too much. Use a little less water next time – when squeezed, the substrate should only release a few drops.
Green or black spots
Contamination – usually the substrate was still too warm when inoculated or the work wasn't clean enough. More in common mushroom growing mistakes.
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.
FAQ about straw pellets
Do I need to pasteurise the straw pellets?
No. The heat during production makes them practically sterile, and the boiling water does the rest.
How much substrate do 5 kg of pellets make?
With twice the amount of water, around 15 kg of moist substrate – for which you need about 1.5 kg of spawn.
Can I grow Shiitake on straw pellets?
Shiitake are wood-loving. Use hardwood pellets in a filter bag instead – see Mushrooms on pellets.
How do I store the pellets?
Dry and sealed. Dry pellets take up much less space than ready substrate.
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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