Production and Harvesting

Mushroom growing is a complex but rewarding undertaking. In this section, find comprehensive information on planting and growing mushrooms such as Agaricus bisporus, oyster, and shiitake. In addition, access resources on mushroom substrate preparation, spawning, caring, pinning, and cropping. Tips on microbial activity and sanitary conditions are included as well.

How to Grow Mushrooms

From the start of composting to the final steam-off after harvest, growing mushrooms takes about 14 weeks to complete. The production process involves six main steps: Phase I and Phase II composting, spawning, casing, pinning, and cropping.

To successfully grow mushrooms, it is critical to ensure adequate management of starting ingredients and proper environmental conditions. Learn more about the latest advances and challenges on subjects such as mushroom cultivation practices, composting, spawn technology, and product quality with Penn State Extension’s Mushroom Short Course.

Making Composted Substrate for Mushrooms

Mushrooms extract the proteins and carbohydrates they need from a rich medium of decaying organic-matter vegetation. This matter is prepared into nutrient-dense substrate composts. Decaying organic matter consists of many naturally occurring organisms (microbes) such as bacteria, fungi, and actinomycetes. To thrive, these microbes require water, food, and oxygen.

Read more about mushroom substrate on Penn State Extension’s Substrate Management page.

Mushroom Spawning

Mushroom spawn is a substance that has been treated with mycelium (thin, thread-like cells). The spawn production process begins by sterilizing a mixture of grain plus water and chalk. Once the mixture is sterilized, mycelium is added and the period of active mycelial growth begins.

Spawn is typically made from a stored culture (millet, rye, wheat) and is used to seed mushroom compost at the end of Phase II. Careful compost preparation can reduce the chances of encountering problems during the spawn-growing period – from spawning time through casing.

Pinning

Pinning is an important part of the mushroom production process that can affect both crop quality and final yield.

Mushroom pins develop once rhizomorphs (thick mushroom mycelia) have formed in the casing. To develop properly, fresh air should be introduced into the growing room, with a carbon dioxide content of 0.08% or lower (depending on the cultivar).

Harvesting Mushrooms: The Cropping Cycle

Mushroom harvest begins 15 to 21 days after casing, which is 7 to 8 weeks after composting started. Mushrooms are picked over a period of 2 to 4 days in a 7- to 10-day cropping cycle (also known as a flush or break). Once the mature mushrooms are picked, the next flush moves towards maturity. Flush timing is managed through water, CO₂, and temperature control.

Post-Crop Pasteurization and Spent Mushroom Substrate

When a crop becomes unproductive it often needs to be terminated. Prior to removal, the spent mushroom substrate is “pasteurized” with steam. Post-crop pasteurization (or steam-off) helps ensure that there are no pests or disease-causing pathogens that can contaminate neighboring or subsequent crops.

Some pathogens can grow into the wood and survive post-crop pasteurization. This is why it’s vital that the mushroom grow room is also steamed after the substrate is removed and the beds are washed down. When steaming off a room with substrate, the temperature should be no less than 150°F for at least 12 hours.

On this page, find additional information and tips on planting, growing, and harvesting mushrooms.