July mushroom grow: A quick guide to growing oyster mushrooms

Cat head, for scale. 

It’s been a few months since my last mushroom grow, so I figured it was time to reunite with some old friends.
In June, I purchased some elm oyster & blue oyster spawn and tried a cold pasteurisation (with hydrated lime) & inoculation of pea straw out in my garden. This is my first time growing on pea straw, it is not generally recommended but I decided to give it a shot anyway. The results were good but not as good as past grows.

To make your own oyster mushroom block, you’ll need:
Mushroom spawn
Straw (wheat, barley, rye) (Oysters can be grown on many substrates such as fresh coffee grounds, cardboard, toilet rolls, books etc.)
Lime (if cold pasteurising)
A bucket with holes drilled in OR mushroom bag w/filter OR laundry basket.

You can cold pasteurise straw with hydrated lime (about 1/2 cup of lime to 10-12L water, soak for approx 12-15 hours) or heat pasteurise the straw, this can be done in small amounts in a pressure cooker.

Once you have pasteurised your straw, allow it to drain and cool down if needed.
At this stage, you can mix in your mushroom spawn (some suppliers sell spawn in the amount needed for 1-2 bags, others only sell large amounts such as 2kg bags. If you are buying a 2kg bag, you can use about an 8th to fill one bag or bucket.)
Spawn is added to the straw by laying straw down and crumbling spawn on top. Repeat this until the bag/bucket is full, remembering to push the straw down to make sure you get as much in as possible. Crumbling the spawn rather than leaving it in big chunks allows more points for inoculation.
Then you simply need to close up the bag (this can be done with masking tape) or put the lid on the bucket.


Over the next few weeks, the mycelium will grow and colonise the block of straw.
Contaminants (i.e mould) will probably occur at some point in your mushroom growing journey. If you notice mould, compost the block and try again. Remember that this is a learning experience and mistakes make compost! If you are particularly hopeful and don’t want to accept the fate of your block that quickly, you can wait and see if the mycelium out-competes the contamination, however, you should isolate the infected block from any others as contamination can spread.

Once your block is colonised (covered in mycelium) you can cut either one large hole or several small holes in the bag for the mushrooms to grow out of, remember, just because you cut the holes there it doesn’t necessarily mean that’s where the mushrooms will grow from so keep an eye on them!
You can start to mist spray your block 1-2 times per day to increase humidity and water content of the mycelium. Mushrooms will generally begin growing within 1-3 weeks of full colonisation.

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Mushrooms first appear similarly to small, raised mounds of mycelium. This is the primordial stage, essentially, those mounds are baby mushrooms. Quickly, they begin to take shape and form ‘pins’ which look considerably more mushroom-ish.

The pins will swell with water and be ready to pick in 1-5 days. While they are growing it is important to keep humidity and air flow high. Lack of fresh air exchange can cause the mushrooms to grow thick stems with very small caps or lots & lots of tiny mushrooms, remember, mushrooms breathe oxygen just like we do!
Mushrooms are made up of up to 95% water, so humidity is also very important. If you don’t have a humidifier, this can be achieved by continuing to spray your block 1-2 times a day.
This grow worked out reasonably well, however I got a bit slack with the air exchange at some points which did lead to quite a lot of smaller mushrooms, although I still managed several clusters of decent sized ones.



Your oyster mushrooms are ready to pick when the caps are flat. These are almost ready to pick, so they will grow a little bit bigger, but not much would be lost by picking them at this stage.
You can twist the mushrooms off at the stem base or cut them off with clean scissors.

Once you have picked your mushrooms, you can submerge your block in water to re-hydrate it and initiate another flush of mushrooms. Dunking in cold water imitates the natural conditions that causes most mushrooms to fruit such as low temperature and lots of water. Submerge the block for about 10-15 hours, or at least an hour for every inch.
You should then drain the block to remove excess water.
Another set of pins should begin forming over the next few days.

Points to remember:
Mushrooms breathe oxygen, give them lots of fresh air.
Mushrooms are up to 95% water, keep humidity high.
Wherever they are growing should be as clean and sterile as possible to reduce chances of contamination.
Different varieties require different temperature conditions.
Try to check on them every day, especially when your block is close to fully colonised!
You will never have 100% success, don’t give up.

Good luck on your mushroom growing adventures!



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