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Mushrooms, being from an entirely different kingdom, behave differently from plants throughout the growing process. They require specialized care and different growing implements to provide the highest yield.

You may be familiar with substrate, an organic material rich in nutrients, as an essential building block of productive growth. However, different growers will use different methods to suit the type of mushroom they’re growing.

If you search around for what other mushroom growers’ yields look like, you may see some that look like they’re budding out of the dirt the way that plants do. How do you get that result? How does that method affect the mushrooms?

Read through this ultimate guide to mushroom casing soil to learn more about your options and what they can do for your growing mushrooms.

What’s a Casing Layer?

When you first begin your mushroom-growing journey, you’ll learn about substrate and spawn bags. Inoculation refers to the “planting” process when you’re working with fungi. You introduce the mushroom spawn to the substrate, keep it moist, and watch over the days and weeks as the mycelium begins to grow.

However, some varieties of mushrooms need more TLC to grow properly. That’s where the casing layer comes in.

Casing is a material—organic, inorganic, or a mixture of the two—that you spread on top of the inoculated substrate. It helps keep moisture inside the substrate to allow those mushrooms to fruit properly. Casing layers with organic material can also provide essential nutrients that the mushrooms need.

Pros and Cons

As with any growing material, there are upsides and downsides to using a casing layer. Think about your growing environment and your preferred type of mushrooms as you make your decision.

Positives of a using casing layer include:

  • Superior moisture retention
  • Humidity control
  • Storage of extra water
  • Introduction of beneficial microorganisms

Potential pitfalls of a casing layer include:

  • Susceptibility to contamination (if you’re using unpasteurized casing)
  • An extra step in the growing process
  • More materials on your shopping list

Whether you choose to use a casing layer at all depends on the type of mushroom you want to grow and the environment where it’ll do that growing. Of course, different types of casings will give you different results—for example, if you do use pasteurized casing, contamination won’t be a huge concern.

Types of Casing

Mushroom growers use a variety of different casings to keep their substrate hydrated and protected. Some growers use regular old potting soil, but you’ve got many options at your disposal.

Peat moss is a heavy lifter in the casing world, as it can hold up to 10 times its weight in moisture. It’s easy to break up and spread over your substrate, and you can use it for plants as well. If you are also an avid gardener, you may already have some lying around!

When you browse the mushroom casing kits we offer at Midwest Grow Kits, you’ll see a list of fascinating ingredients included in our casing. One of the key components we use is an organic compound called coco coir.

Coco coir, or coconut coir, derives from the material between the husk and the outer coating of a coconut seed. In humanity’s eagerness to find things to do with the coconut—shred it, slice it, or turn it into milk—we often left this stuff by the wayside. However, coco coir is an essential component of any hydroponic growing situation. While it is inert and does not contain any nutrients on its own, coco coir is perfect for retaining moisture and discouraging insect activity.

Lime and vermiculite are common additives to casing material, as they raise its pH and help pasteurize it. The right casing layer will help keep contaminants out instead of encouraging them to seep in.

How To Case

If you’re ready to grow mushrooms with a casing layer, pull out your grow kit and start the process as you normally would. Carefully introduce your spawn bag to your substrate and spread it all out to prepare for inoculation.

Before you walk away, pull out your casing bag and gently spread a layer on top of your substrate. The casing layer should be at least half an inch deep (but no more than one inch). It’s best to work in a sterile environment for this step, so wash your hands thoroughly and slip on a pair of nitrile gloves beforehand!

Now it’s time to place it all into the fruiting chamber. Check on your growing mushrooms every day; within a week, you should see some tiny caps beginning to burst forth. As those caps grow in size, keep a close eye on the humidity levels in your growing environment. Any loss of moisture can impede their growth or even abort those little caps.

Once your mushrooms have grown to their full, recognizable size, use a clean harvest knife to gently snip them at the base of the stem. Get as close to the casing layer as you can and shake off any extra that sticks to your mushroom.

Now that you’ve harvested this first batch of mushrooms, you’re ready to begin the cycle anew!

Flush It Out

When you keep them in a humid and well-maintained environment, mushrooms can grow in perpetuity. You’ve just got to keep that process going soon after each harvest. After you gently harvest all the mushrooms on your fruiting block, you’ve got a couple of options to start growing again.

The first and easiest way to flush is to place that block right back in the fruiting chamber after harvesting the first round of mushrooms. Within a week, you’ll see some new mycelium growth and another smattering of tiny caps. The new mycelium often envelop the stumps left over from your initial harvest but beware of contamination. When you complete your harvest and flush out your fruiting area, use sterile tools and wear gloves.

Your other option is to spread out a fresh casing layer. Remove the original casing, scrape the top of that substrate block with a fork or your gloved fingers, and spread out a layer of fresh casing. (You could also reapply your original casing if you’d like. “Tilling the soil” helps create new growth opportunities and refreshes the growing environment!)

There are multiple processes involved in growing high-quality mushrooms at home. Some of those steps are mandatory for growth, while others lend a strong helping hand. Consider using a casing layer next time you grow mushrooms to seal in moisture and maintain an optimal growing environment. Midwest Grow Kits’ ultimate guide to mushroom casing soil can help you make smart decisions that will help your next harvest flourish!

The Ultimate Guide to Mushroom Casing Soil