How to Grow mushrooms on your used coffee grounds…

Oyster mushrooms love and thrive on the nutrients in used coffee grounds. Collect your own or ask your local coffee shop to give you theirs. Espresso grounds are best for growing mushrooms, as the coffee-making process means your substrate is already pasteurized, hydrated and ready to grow.

When: Year-round.

Where: You will need to leave your kit to incubate for 21 days in the dark at a constant temperature of 17–20 ̊C (63–68 ̊F). Once innoculated and ready to grow, place in a bright spot where you will remember to water it and be able to watch it grow – next to the kitchen sink or on a windowsill is a good option.

How: If you want to get growing the best starting point is to pick up one of our Coffee Kits from our online shop,

Within our kits you’ll get a full set of instructions and a pack of Grey Oyster spawn.

Before you start: you’ll need to collect your used coffee grounds.  You will need 750g-1kg max.   But dont worry - your spawn will keep refrigerated for up to one month after receipt - giving you time to collect your coffee.

Not a big coffee drinker?  No problem! You can collect used coffee grounds from your local café – or even give used tea bags a go.

Your kit contains:

- Grey Oyster mushroom grain spawn inside a mushroom grow bag with    

  filter patch.

  Keep your spawn refrigerated until ready and use within one month.

- A sticker to seal your grow kit.

You will need:

- A lidded container or zip lock bag - to collect coffee grounds, and store in your freezer.

- Used coffee grounds - either collected over time at home and stored after each brew in your freezer.  Or you can ask your local coffee house.  We suggest collecting 800g - 1Kg of used coffee grounds prior to setting up your kit.

- A desert or table spoon

- Mister/spray bottle - to water your kit.

PLEASE NOTE: You should freeze your coffee immediately after brewing, breaking up any large lumps with a clean spoon first.  The freezing helps preserve the coffee and reduces the chance of contamination during the incubation period. 

Defrost over night, or on the same day you make up your kit.

If you’re collecting from a coffee house the coffee must be freshly brewed that day and you’ll need to use it within 24 hours of being collected, you can freeze it if this is not possible.

The brewing process pasteurises and hydrates the coffee, and this helps ensure there is less risk of your grounds having been contaminated.

How to get started:

Defrost your coffee grounds (allow for 6 - 8 hours).

Wash your hands, utensils and work surfaces to reduce the risk of contamination throughout this making and the inoculation process.

Remove your bag of spawn from the fridge and allow it to reach room temperature - squeeze the bag to break the spawn up, keeping the bag sealed at this time.

Next - open the top of your grow bag with your spawn inside - your spawn should smell fresh and mushroomy and not sour. 

Using a clean spoon, scoop your coffee grounds into your mushroom grow bag, mixing your coffee into your spawn as you go. 

Do not fill the bag above the bottom line of the filter patch.

Once all the spawn is evenly distributed amongst the coffee grounds, seal your grow bag at the top. Don’t compact the coffee mixture and make sure you leave a good air gap at the top.

To seal your mushroom grow bag, fold the top over a couple of times, use the sticker provided, making sure not to cover the white filter patch - spawn is a living organism and needs a good supply of oxygen to thrive.

Place your grow bag in a dark location at a stable temperature of 17-20°C. Any fluctuations in temperature could cause moulds to grow.

After 21 days your substrate block will be fully colonised and covered in white mycelium.  Your kit will also feel firm to touch.

You can see a short video of this process on our Instagram HERE.

Getting Growing:

Once your substrate block is ready to grow, pop it into your fridge overnight - this is to cold shock your kit into fruiting.

You want to introduce light, oxygen and humidity to your substrate block, to initiate fruiting.

First fold down the top of your grow bag, covering the filter patch.  Then, with clean scissors cut a 12cm ‘X’ shaped opening in the front of your plastic bag.

Spray the opening twice a day; and more regularly in warmer weather. This keeps the opening humid and will encourage growth.

Unlike plants you are not needing to water the substrate inside the bag - keep the plastic over the opening and don’t cut or peel it back in any areas. You mushrooms will grow towards the humidity outside caused by the water needing on the plastic.

If you find the weather or environment is too warm and the water is evaporating quickly - you can place your kit on a sauce of water, and drape a clan tea towel over the top. By keeping the tea towel damp this will maintain a humid environment for your mushrooms to grow towards.

Once you start to see your Oyster mushrooms appear, they will need to be sprayed twice a day to keep them hydrated and to stop them from drying out. You will see your mushrooms grow rapidly over the next 1-2 weeks.

Pushing back the plastic opening as they need the area to grow.

When to harvest:

Your mushrooms should be ready to harvest 5-7 days after they first appear.  To remove, pinch and twist close to the base of your cluster.

For the perfect pick think about harvesting your Oyster mushrooms when their caps start flattening out.

Once you have harvested your Oyster mushrooms, they’ll keep well inside a paper bag and stored in the fridge until you’re ready to eat them.

How to get more mushrooms from your kit:

You could try for a second flush, by letting your kit rest, this gives the mycelium a chance to regrow.

Place your kit in a dark cupboard with a stable temperature.  You’ll need to tape closed the original opening during the rest phase to minimise your risk of contamination.  You can then start again by putting your kit in the fridge for 24 hours, then reopening and soaking your substrate block for 4-6 hours in clean, cold water.  Remove any standing water from your kit and repeating the growing process. Each cycle will increase the risk of contamination, so look out for any green spots within the bag.

When you have finished growing: Remove your substrate from the plastic bag - you can recycle the plastic at any large supermarket facility.

Your fruiting block should be left to dry out then disposed of into your compost bin or with your household food waste.

Happy growing.

If you have any questions or curiosities during your growing journey, be sure to explore our FAQs and troubleshooting blog. Each post offers insights into the fascinating world of mushroom growing - from the simplicity of our easy-grow kits to helpful advice when nature takes an unexpected turn.

Ⓒ Caley Brothers 2025

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