Michael Davis
Casing is a fruiting method where a colonized substrate is covered with a layer of moist material to aid with moisture retention and induce fruiting. The casing layer is placed on top of a colonized substrate before fruiting to create a consistently humid environment and make up for less-than-ideal growing conditions. The main purpose of the casing layer is to protect the colonized substrate from drying out and to support the growth of beneficial microorganisms. While not all mushroom species require a casing layer, yields are enhanced with its application.
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What You'll Learn
Casing layer composition
The casing layer is a layer of moist material—organic, inorganic, or a combination of both—placed on top of a colonized substrate to induce fruiting. It helps create a microclimate that encourages pinning and aids in moisture retention in the substrate. The casing layer is typically between 0.25 and 0.5 inches thick and is applied after the substrate has been fully colonized by mycelium, which is indicated by the substrate turning completely white.
The materials used for the casing layer are chosen for their ability to retain water, which is crucial for maintaining optimal fruiting conditions and initiating fruit body growth. Vermiculite, for example, is used in most casing recipes due to its inert nature and high water-holding capacity. It is inexpensive and readily available at garden and hydroponics shops. Peat moss, another common ingredient, is unconsolidated soil material that consists of organic matter accumulated under excessively moist conditions.
Coconut coir, the crushed outer shell of the coconut fruit, is also used in casing layers due to its excellent water retention capabilities and nutritional content. However, its nutrition can lead to mycelium growth over the casing. To prevent this, mineral supplements such as gypsum, hydrated lime, and limestone flour can be added to provide essential minerals and balance the pH, making the casing less hospitable to fungal contaminants.
While the casing layer helps induce fruiting and provides moisture, it is susceptible to contamination. Therefore, pasteurization is recommended before application. This can be achieved by simmering the casing mixture in a pot for 45 to 60 minutes at a temperature between 65°C and 80°C. After application, the cased blocks are placed in a fruiting chamber, and the humidity is maintained to ensure the casing layer does not dry out completely.
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Benefits of using a casing layer
While not all mushrooms require a casing layer, it is a technique that offers multiple benefits. The primary purpose of a casing layer is to create an ideal environment for mushrooms to flourish.
A casing layer is a layer of material, organic, inorganic, or a combination of both, added on top of a colonized substrate. It helps to retain moisture in the substrate, preventing it from drying out. This layer provides a consistently humid microclimate, where mushroom pins can form and develop into fruit bodies. The casing layer acts as a water reservoir, supplying moisture to the developing mushrooms. Additionally, it supports the growth of beneficial microorganisms, which are necessary for fruit body formation in some species.
The materials used for the casing layer, such as peat moss, vermiculite, or coconut husk fiber, are chosen for their ability to hold water, which is crucial for maintaining proper fruiting conditions and initiating fruit body growth. By using materials that can retain moisture, the casing layer helps to optimize the growing environment, leading to enhanced yields.
Furthermore, the casing layer can be pasteurized or treated with hydrated lime (calcium hydroxide) to ward off contamination and inhibit the growth of mould and bacteria. This treatment raises the pH of the casing layer, making it inhospitable to fungal contaminants.
In summary, the benefits of using a casing layer include moisture retention, providing a humid microclimate, supporting beneficial microorganisms, optimizing yields, and reducing contamination. While adding a casing layer introduces an extra step in the growing process, it can significantly enhance the performance and yield of mushrooms.
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Drawbacks of using a casing layer
While a casing layer can provide a consistently humid environment for mushrooms to grow, there are several drawbacks to using one. Firstly, it adds an extra step to the growing process, which means more time and resources are required. This additional time is needed for the mycelium to adapt and react to the new conditions, which can cause frustration for growers who want results fast.
Another drawback is the potential for over-colonization or "overlay", where the underlying mycelium completely overruns the casing layer. This can result in a dense layer of mycelium growing on top of the casing layer, hindering the formation of pins and even halting growth. Overlay may be caused by high carbon dioxide levels, a dry casing surface, low relative humidity, or a high temperature in the fruiting chamber.
Furthermore, casing layers can be susceptible to contamination, especially in fruiting environments with limited fresh air. While pasteurization or treatment with hydrated lime can help prevent this, it adds an extra step to the process. Overall, while a casing layer can be beneficial for mushroom growth, it is important to consider the potential drawbacks and take steps to mitigate them.
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Preparing the casing layer
Step 1: Pasteurization
Before applying the casing layer, it is essential to pasteurize it to reduce the risk of contamination. This can be done by placing the casing mixture in a mushroom grow bag and simmering it in a pot for 45-60 minutes. Ensure that the centre of the mixture reaches a temperature between 65-80°C and maintains that temperature for about 30 minutes. This process eliminates any harmful microorganisms that could hinder mushroom growth.
Step 2: Cooling
After pasteurization, allow the casing layer to cool to room temperature before applying it to the substrate. Adding a hot casing directly to the block can kill the mycelium, preventing the mushrooms from fruiting. This step is crucial for the well-being of your mushrooms.
Step 3: Applying the Casing Layer
Once the casing layer has cooled, it's time to apply it to the colonized substrate. Make sure the substrate has been fully colonized by mycelium, evident when it has turned completely white and covered at least 95-100% of the substrate. As a general rule, provide a casing layer between 0.25 and 1 inch thick for every inch of substrate. Spread the casing mixture evenly across the top of the substrate using a clean, gloved hand, ensuring it remains loose and is not packed down.
Step 4: Placing in the Fruiting Chamber
After applying the casing layer, place the newly cased blocks in a fruiting chamber. Maintain the humidity at an appropriate level to encourage mushroom growth. Be careful not to let the casing layer dry out completely, as this can hinder the pinning process.
Step 5: Monitoring and Adjusting
Within 4-7 days of placing the cased blocks in the fruiting chamber, you should start to see pins forming through the casing. At this stage, ensure that the humidity is carefully controlled to promote mushroom growth. If the environment becomes too dry, the pins may abort, so a consistent moisture level is crucial.
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Application of the casing layer
The casing layer is a layer of moist material—organic, inorganic, or a combination of both—placed on top of a colonized substrate to induce fruiting. It aids in moisture retention, which is crucial for maintaining optimal fruiting conditions and initiating fruit body growth.
The application of the casing layer involves the following steps:
- Preparation: Prepare the casing mixture, which can be organic, inorganic, or a combination of both. Common organic options include peat moss and coconut coir, while inorganic materials such as vermiculite are also used. The chosen material is mixed with water to create a moist, loose consistency.
- Pasteurization: Before applying the casing layer, it is recommended to pasteurize it to reduce the risk of contamination. This can be done by placing the mixture in a mushroom grow bag and simmering it in a pot of water for 45-60 minutes, ensuring that the center reaches a temperature of 65-80°C for at least 30 minutes.
- Application: Cut open the bag of colonized substrate and pour a small portion of the casing mixture on top. Spread the casing mixture uniformly to a depth of about 0.25-0.5 inches. It is important to ensure that the casing remains loose and is not compacted.
- Incubation: After applying the casing layer, seal the bag of colonized substrate and return it to a dark place. Monitor the substrate over the next several days for signs of colonization.
- Fruiting: Once the casing is applied and colonization is complete, place the newly cased blocks in a fruiting chamber. Maintain humidity to encourage the formation of pins. After 4-7 days, pins should start to appear through the casing. Continue to monitor humidity levels as the mushrooms grow.
- Harvest: Once the mushrooms reach a suitable size, it is time to harvest. Cut the mushrooms at the base of the stem, close to the top of the block. Brush off any excess casing stuck to the mushrooms. After the initial harvest, you can encourage a second flush by returning the block to the fruiting chamber and maintaining optimal conditions.
The application of the casing layer is a crucial step in mushroom cultivation, providing the necessary moisture retention and environmental conditions to induce and support fruiting. By following these steps and maintaining careful control over humidity and contamination, growers can successfully cultivate mushrooms using a casing layer technique.
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Frequently asked questions
A casing layer is a layer of moist material, organic or inorganic, placed on top of a colonized substrate before fruiting. Its main function is to aid with moisture retention in the substrate.
A casing layer helps induce fruiting and provides moisture to the substrate and developing fruits. It also protects the colonized substrate from drying out, provides a humid microclimate for mushroom primordia to form and develop, and supports the growth of beneficial microorganisms.
Materials used for casing layers are often chosen for their ability to hold water, which is essential for maintaining proper fruiting conditions and initiating fruit body growth. Examples of materials include peat moss, vermiculite, and coconut coir.
