Substrate Management

A good substrate helps to ensure adequate crop growth and nutrition. Finding the right mushroom substrate is a vital aspect of any mushroom production. On this page, access Penn State Extension’s educational resources on mushroom substrate management, including seeding substrate and managing Agaricus bisporus.

Mushrooms Substrate Preparation

In order to get energy, carbohydrates, and proteins, mushrooms require organic-matter vegetation. The matter is carefully prepared into nutrient-rich substrate compost by using bulk ingredients such as wheat straw and hay.

If the bulk materials are high in nitrogen, mushroom growers may add other high-carbohydrate ingredients, such as corncobs and cottonseed hulls. Additional nitrogen supplements may be added to the composts, as well.

Mushroom substrate preparation and production (also called composting) is divided into two main stages – Phase I and Phase II. The first phase begins by mixing and wetting the ingredients as they are stacked in piles.

In Phase II composting, the substrate is filled into a mushroom-growing system and pasteurized to both remove harmful microbes and preserve good substrate microbes. During the second stage, the composting process is completed and all remaining ammonia and simple soluble sugars are eliminated.

Mushroom Spawn

Spawn is a material used to "seed" mushroom composts. The process of making spawn involves a mixture of grain and calcium carbonate that is cooked, sterilized, and cooled. Mycelium (thread-like cells) is placed in small batches on the grain.

The amount of spawn used depends on the length of the spawn-growing period, as well as the compost fill weight. In general, using more spawn will result in a more efficient use of substrate nutrients.

Uses of Spent Mushroom Substrate

Mushrooms are typically cultivated using substrates made of natural ingredients. A casing layer of peat moss and ground limestone is added on top of the substrate to provide support for the growing crops.

The soil-like material that remains after a mushroom crop is known as spent substrate. While it still contains some nutrients, it is often more economical to start a new crop. Before being removed, the spent mushroom substrate is “pasteurized” to kill any pathogens or pests that may be present.

The spent mushroom substrate can be utilized in a number of ways. It can be spread on top of newly seeded lawns to hold the water in the soil during the seed germination process. Spent substrate can also be used as a soil amendment, adding organic matter and structure to the soil.

In this section, discover additional information and tips on managing and utilizing mushroom substrate.