Note: Adding straw is not vital if you grow in small quantities of 1kg substrate bags or less.
For 1kg substrate or more you will often find that the coffee grounds become too compacted.
This happens because the coffee ground particle size is very small. This means the substrate can become too dense and compact, creating poor air exchange for the mushroom spawn.
Adding straw or hydrated sawdust pellets breaks up the density of the coffee grounds and creates better air exchange in the substrate.
Step 3: Incubate growing bags for 2-3 weeks
- Leave your grow bags in a warm (20-24C) and dark place
- Check every few days to see the white mycelium starting to grow across the coffee
- After 2-3 weeks your bags should be fully colonised and bright white
Step 4: Place in fruiting conditions
- Cut 2-5cm hole in your grow bag
- Place in a shaded spot with some indirect light (Oyster mushrooms need some light to grow properly)
- Spray with water each day
- Mushrooms will begin to start growing in around 5-10 days
- Keep spraying regularly for another 5-7 days as they double in size each day
Step 5: Harvest!
- When the top of the caps begin to flatten out it’s time for harvest
- Twist the cluster off of cut with a knife
- Cook them up and enjoy the satisfaction of eating mushrooms grown from coffee waste (no, they don’t taste of coffee!)
- After 2 days, submerge your bag in water overnight to rehydrate the substrate
- Then spray daily to encourage the 2nd crop to grow
The # 1 Mistake to avoid when growing mushrooms on coffee waste
Growing mushrooms is all about providing the mycelium with the best chance to win an extremely competitive race with competing moulds.
If you’re not already aware, mushroom mycelium is a white root-like network, and is the main part of the organism from which mushrooms grow.
This mycelium grows throughout the substrate (the food source) and must completely colonise it before it is able to grow mushrooms.
Traditional mushroom growers sterilise or pasteurise the material they’re growing on before they add the mushroom spawn.
This is usually done by steaming the substrate which is both energy intensive and costly.
The beauty of growing on coffee grounds is that the brewing process pasteurises the grounds for us.
The coffee does not stay like this for long though.
The biggest mistake you can make is to use coffee which is too old and already has other organisms like mould starting to grow on it -> only use fresh coffee grounds less than 24 hours since brewing.
You can’t always see this with the naked eye but if the coffee is more than 24 hours old you’re more likely to grow mould instead of mushrooms.
We pick up coffee on a daily round so we know it’s clean for our mushrooms.
You could just ask your local cafe if you can pick up their grounds at the end of the day or the following morning to make sure it’s fresh.
Growing mushrooms in coffee grounds just makes so much sense.
You make use of a plentiful waste resource which is still packed full of nutrients and turn it into delicious healthy Oyster mushrooms instead.
At the end of the growing cycle you can return the now composted grounds to enrich your soil and complete the circle.
Interested to have a go at this yourself? Check out our guide to Growing Oyster Mushrooms; this goes in to more depth and offers additional growing tips.
And if the idea has really inspired you then you may be interested in our articles on How To Set Up A Low Tech Mushroom Farm and How To Grow Mushrooms Outdoors With A Mushroom Bed.
You can also join our free email series & take a tour around our small scale mushroom farm by signing up below: