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How to grow mushrooms indoors

Claire Ratinon/PA.

By Hannah Stephenson
I’ve often wondered about foraging for mushrooms, but the thought that I’d pick a poisonous one always got the better of me.

However, I’ve now learned from organic food grower Claire Ratinon that it’s possible to grow healthy mushrooms on my windowsill at home, without any chance of poisoning myself.

“They are edibles which have gone totally under the radar, yet we eat them all the time,” says Ratinon, author of new book How To Grow Your Own Dinner Without Leaving The House.

“When people learn about the magic of mycelium, a whole world of mushroom geekery is unleashed,” she enthuses. “They are so beautiful as you watch them emerge.”

Mushrooms occupy their own kingdom of biological classification and behave completely differently from plants, so cultivating them for eating requires a different approach. Ratinon offers her tips on where to start, how to keep them going and when to harvest…

What do I need?
“You can buy mushroom growing kits created for you using an appropriate food source or ‘substrate’, such as spent coffee grounds. It’s a cool way to reuse what would otherwise be a waste product,” explains Ratinon. “There are companies that also use straw or hay or other materials which mycelium (fungus system) would live on.” She recommends GroCycle ( for kits.

“They basically introduce the spores of a mushroom into a substrate,” she continues, “on which the spores would populate the soil or the wood, if it were growing in its natural state.

“Then you effectively ‘shock’ the substrate, giving it a stimulus to grow, which could be exposing it to light and spraying it with water, which is what makes your mushrooms shoot.

“Once you go through using the kits, you get an idea about how the science works and the mechanics of the process.”

What do I do with a kit?
Kits generally come with a tray. The food source will already have been sterilised and the spores introduced, and will arrive in a plastic bag, into which you make holes to allow the mushrooms to emerge.

“Don’t empty the contents of the bag into the tray,” says Ratinon. “It may not look like coffee, it should be fairly white as it is full of the mycelium. You’ll need to mist it with water twice a day to keep the conditions humid and the mushrooms moist.”

What happens next?
“You’ll start seeing little pinheads appear, which is the start of your mushrooms beginning to fruit. It will happen where the holes are,” she says.

Do mushrooms need sun?
They don’t need sunlight to grow because they don’t photosynthesise, she explains, although they will grow towards the light. But they could even be left in a shed or in a north-facing basement.

“Consistency is always key,” Ratinon continues. “Extreme temperatures are to be avoided. Once you have [your kit] in a place, keep it there at a moderate temperature. But they are pretty forgiving.”

How much space do you need?
“Only as much as a mushroom kit takes up, less than a windowsill.”

How long do they take to harvest?
“Within three to four days you will see tiny mushroom pinheads appearing. It only takes a few more days to get full-sized oyster mushrooms. It’s amazing.”

How do you know when to harvest?
When the mushrooms have been doubling in size for a few days and the edges of their caps are beginning to turn up, you can harvest them by cutting them off at the base with a sharp knife, Ratinon advises.

“You can get up to three flushes – two good ones and then a lesser one – from one kit. They run out of steam after that,” she notes.

What types of mushroom can you grow in this way?
“It tends to be mostly oyster and shiitake, but I’m sure the process lends itself to most edible mushrooms,” she says.

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