Lime and gypsum are commonly used together in mushroom substrates for several important reasons:

1. pH Adjustment: One of the primary reasons for using lime and gypsum in mushroom substrates is to adjust the pH of the substrate. Mushrooms grow best in a slightly alkaline environment with a pH level between 7.5 and 8.0. Lime (calcium carbonate) is used to raise the pH of the substrate, making it more alkaline, which is essential for the growth and development of many mushroom species. Without adequate pH adjustment, mycelium may struggle to thrive and produce mushrooms.
2. Nutrient Availability: Gypsum (calcium sulfate) is added to the substrate to provide a source of calcium and sulfur. These minerals are essential for the growth of mycelium and the development of mushrooms. Calcium plays a crucial role in cell wall formation and stability, while sulfur is involved in various metabolic processes. Providing these essential nutrients through gypsum ensures that mycelium has what it needs for healthy growth.
3. Moisture Retention: Lime and gypsum also play a role in retaining moisture within the substrate. By adding them in the recommended ratios, you can create a substrate that retains moisture effectively. This moisture retention is vital for the proper development of mycelium and mushroom fruiting bodies. It helps prevent the substrate from drying out prematurely, which could hinder mushroom growth.
4. Casing Mix Recommendation: In the context of casing mix, a 50-50 ratio of gypsum to lime powder is suggested. This balanced mixture ensures that both pH adjustment and nutrient availability are optimized for mushroom growth. The casing mix is the outer layer of the substrate where mushrooms form, so it's crucial to provide the right conditions for fruiting.
5. Consistency and Convenience: The product you mentioned contains two separate bags of fine food-grade lime powder and gypsum powder. By providing these components separately, it allows users to adjust the mix according to their specific substrate requirements while ensuring food-grade and lab-grade quality. The resealable pouches also help maintain the freshness and quality of the materials.

In summary, lime and gypsum are used together in mushroom substrates to create the ideal pH environment, provide essential nutrients, retain moisture, and promote healthy mushroom growth. The 50-50 ratio of gypsum to lime in casing mix is a recommended practice to ensure the success of mushroom cultivation.