Growing mushrooms indoors: Incubation and grow rooms

Have you ever felt less productive on a scorching hot summer’s day? The mycelium in our growing medium sure has.

As temperatures in the Ottawa Valley rose during the summer, so did the temperature in our incubation room. This room houses the mushroom grow bags where the spores release hyphae that feed on the substrate, eventually developing mycelium. (Don’t worry, this article explains what those fancy words mean). This process is called the spawn run.

White mycelium starting to appear in the brown growing medium.

White mycelium is starting to develop and connect with each other in a Pioppino mushroom grow block.


The ideal temperature for a spawn run depends on the type of mushroom, but it is generally between 23 and 28 Celsius (73 and 82 Fahrenheit). The temperature in our incubation sat around 31 Celsius (86 Fahrenheit). 

It took longer for the blocks to develop mycelium as a result. Hotter temperatures can harm or kill mycelium growth, leaving parts of the growing medium without any development. The summer weather plays a factor, but the mycelium decomposing the growing medium produces heat as well. 

We had no choice but to clear out most of the room, losing a trailer load of bags in the process. However, we saved some mushrooms by temporarily moving them to the Deep Roots Food Hub root cellar.

New air conditioning came to the rescue recently, and production is back to as normal as normal can be for a relatively young business.

White mycelium covers most of the growing medium.

When the spawn run finishes, the growing medium usually goes from a brown mix to a solid, white block. The white mycelium is all over the substrate and finding the most oxygen to grow the fruitbody. 

Shiitake mushrooms are different. They stay in the incubation room until the block reaches a golden brown colour. While the other mushroom varieties stay in the growing bags, the Shiitake blocks come out of the bags when heading to the grow room.

Click here to grow mushrooms like the Italian Oyster at home.

Now is when we say goodbye and you say welcome to our grow kits. Up to now, all our indoor mushroom products go through the same stages. Most blocks head to the neighbouring grow room. We select some of the best blocks to use for grow kits. We give you the bag, a humidity tent, a spray bottle, and instructions – all you need is water, time, and somewhere in your house that’s out of direct sunlight or heat sources. 

It's time to take our journey five steps to the left of the incubation room where we find our grow room. It is 24 feet long, almost the length of a school bus and has two aisles with three rows of shelves.

Each shelf is three mushroom blocks deep. We cut the bags with two X’s on one side, fold over the top to let the air out, and place the blocks back-to-back. There is no space between the blocks, except for the Shiitake mushrooms, which have enough space for mushrooms to grow from the side.

Walking into the room is sometimes like entering a cloud. The air is misty – two humidifiers are tasked with keeping the room between 75 per cent and 90 per cent humidity. There is refreshingly cooler air in the grow room, compared to the heat in the main area during the summer. The temperature hovers between 18 and 20 Celsius (64 and 68 Fahrenheit). 

We make the rounds every day to check which mushrooms are ready to harvest, which need more time, and which aren’t up to par. Once a week, we remove about 100 blocks from the grow room at once and fill it up with bags from the incubation room. 

When blocks are finished, we rip off the bags and put the remaining mushroom compost in garbage bags to sit in front of our shop. Those bags are free for you to pick up, as they can support healthy soil in gardens

The harvested mushrooms all go in boxes and relax in the walk-in cooler before they head to whatever’s next. Most of the mushrooms stay fresh and are delivered to restaurants, shops, and customers in the Ottawa area. Others come with us to farmers' markets across Ottawa. Older mushrooms are great to dehydrate and either enjoy as they are or to pulverize into a powder.  

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