Growing mushrooms

For mushrooms to thrive, they require expertise, care and controlled growing conditions. If you’ve ever been curious about how mushrooms grow, here’s a quick snapshot.

Spawn (mushroom seed)

Mushroom seed – or spawn – is essential to growing quality mushrooms. Each of our mushroom farms are supplied with Amycell (licensed genetics) spawn. Costa also supplies other growers both locally and overseas with quality spawn.


Before we plant the spawn, we must prepare its food. Nutrient-enriched compost is the essential food source for mushrooms, and we ensure each of our farms around Australia has access to our premium quality compost mix.

This compost mix is spread on the large composting floors, and the composting process begins as the temperature rises. The straw is broken down and darkens, and over the course of about 20 days, the compost matures. Upon maturation, the compost is referred to as the growing substrate. It’s now ready to go into the growing trays for pasteurisation.


Pasteurisation is required to ‘cleanse’ the compost. We do this by placing filled trays into growing rooms for seven days, preparing for spawn (mushroom seed planting).

Mushroom seed planting

The trays are now ready for spawn (mushroom seed planting). Once the spawn has been added to the substrate, it is watered for up to 16 days – at which time a root system starts to develop.  

Casing layer

Now, the growing trays are ready for a casing layer, or peat. This acts as a reservoir for water, enabling mushrooms to grow. Once the casing layer has been added, it takes about 15 days for the mushrooms to break through. During this time, mushrooms are placed into growing rooms that have optimised humidity/temperature levels to create a perfect environment for mushrooms to grow. Our growing team carefully monitors each crop to ensure the mushrooms thrive.


An abundance of white and brown mushrooms appear, and they double their size every 24 hours! Once ready, they are carefully hand-picked by our highly trained pickers and graded to ensure only the best quality mushrooms are supplied to our consumers. 

Each crop has a harvesting window of only about 26 days. Once we have exhausted mushrooms from the crops, the rooms are sealed and steamed at high temperatures to cook the compost before it is sent off to nurseries for sale as mushroom compost. Then, the process begins again!