Growing mushrooms at home is a fascinating way to expand both your garden and gardening knowledge and increase the home grown food you produce. It’s also super rewarding getting to watch their growth, then enjoy fresh mushrooms that can be cooked in so many ways.
Oyster mushrooms are a very popular type of mushroom because they’re one of the easiest mushrooms to grow, they’re not picky about their growing substrate, and they produce gorgeous mushrooms!
Oyster mushrooms also fruit (i.e., produce mushrooms) after 3 to 4 weeks, which isn’t very long and it’s more waiting than it is work. Once you put together the right Oyster mushroom substrate and mushroom spawn, the mycelium will grow on its own and most of the work is already done.
There’s actually a wide variety of materials you can use for making an Oyster mushroom substrate, since it’s a very low maintenance mushroom. In this article, I’ll explain what a substrate is so you can understand how the different materials change the process and outcome.
What Does Substrate Mean?
A substrate is the material that the mushrooms fruit from, so really anything that a mushroom grows on is its substrate. It’s not a perfect metaphor, but you can think of a mushroom substrate as the potting soil for mushrooms.
In a similar way to how plants grow roots and receive nutrients from them, mushrooms grow from a mycelial network. The mycelium grows through the substrate, using its moisture and nutrients to spread and, eventually, produce mushrooms!
As with plants, different mushrooms have different needs and this is why there are some substrate mixtures that work better for certain kinds of mushrooms, but not for others.
In order for the spawn to create a whole mycelial network and grow mushrooms, the spawn have to become the dominant organism in the substrate. Unlike growing plants, mushrooms are fungi and therefore compete with other fungi and bacteria in the substrate for nutrients.
Regular potting soil often doesn’t work as a substrate because it’s so nutrient dense that it supports a whole bacterial ecosystem- which is great for your plants, but not for growing mushrooms.
So, the ideal substrate is a mixture that allows the mushroom spawn to thrive and eventually take over, so it receives maximal nutrients and can produce mushrooms!
What Makes a Good Substrate?
The central role of the substrate is to provide support for the mycelium, both in terms of structural support and nutrients.
Your substrate is a source of Nitrogen for the mycelium, an essential element needed for mycelial growth. However, too much of it can encourage other fungal growth.
The mycelium needs 50 to 70% moisture in the substrate to produce those really nice, full mushrooms that we love. If your substrate material is too wet, you’ll likely get lots more mold than mushrooms, but if it’s too dry the mycelium won’t grow to be strong enough to fruit.
Generally, it’s best to have a substrate with a pH around 5 to 6.5, however Oyster mushrooms are less picky and can even grow in substrates at 7 or 8 pH.
Along with all these nutritional factors for creating a substrate, the texture and consistency matters a lot. Mycelium loves to grow on materials that are made of lignin, cellulose, or hemicellulose- basically, stringy and dense organic materials.
There needs to be enough space for air exchange because the mycelia will take in oxygen and release CO2- just like us! If your substrate mixture is too dense, this will block the airflow and can lead to contamination.
Factors to Keep in Mind
There are a few things you want to consider when making an Oyster mushroom substrate, especially because they’re so versatile and can work with many materials.
First off, think about what’s most accessible to you. Since you have so many options for an Oyster mushroom substrate, it’s best to use whatever materials you can easily get.
Many agricultural by-products work as great material for substrates which is why, for example, many mushroom growers in cities will use coffee grounds to grow on, since it’s easy to get lots.
Materials like sunflower seed shells, soybean hulls, or corn husks work great for substrates and are materials you would compost anyways. This is a fantastic way to reduce waste and ensure that everything gets put to use in your system.
This is also cheaper than ordering specialty products, which is the next factor: price. Think about how much you’re willing to spend on substrate materials.
Although none of the substrate materials in this post are super expensive or exotic, there’s still price differences. If you’re looking to save money, you may want to opt for materials that you might already have, like chopped straw or vermiculite.
Lastly, are you just growing Oyster mushrooms or wanting to grow other types of mushrooms? If you’re planning to grow several types, then you should research what kind of substrate those other types need and maybe you can use a material that will work for all of them.
Now, I’ll explain the most commonly used and preferred materials for making an Oyster mushroom substrate and then tell you exactly how to start growing!
Chopped straw or straw pellets can be used as substrate.
Straw Pellet Substrate
Making a substrate out of straw pellets is hands down the most popular way to grow Oyster mushrooms and is definitely the best move for beginner or small-scale growers.
Growing Oyster mushrooms on a straw substrate is the tried and trusted material for Oyster mushrooms and using pellets not only simplifies the process, but also increases how many mushrooms you can grow.
One great reason for using straw is that bacteria really doesn’t grow on straw, so you have a very low chance of contamination. What’s even better is that straw pellets have already been processed and treated, which means they don’t need to be pasteurized- a step I’ll explain later.
Many growers who have tried different substrate materials have all found that straw is the best Oyster mushroom substrate. It seems that straw has just the right amount of moisture and its texture provides airflow and space for the mycelium to move around.
Straw isn’t necessarily the top pick for all mushrooms, but growers universally agree that it’s best for Oyster mushrooms. Many growers also love straw substrates for growing King Oysters.
You can definitely use chopped straw, but straw pellets are the most preferred substrate and tend to be easier to work with. They’re already sterile, so this will decrease any chance of competing organisms and it removes one step from the growing process, both great advantages for beginner growers.
Straw pellets are also widely available and in small batches, another reason why they’re great to start with.
Soybeans with the hulls still on, which will be removed during processing and can be used as substrate.
The Master’s Mix is a substrate mixture created by TR Davis from Earth Angel Mushrooms, a man who’s been home growing mushrooms for many years and found that this mixture works very well, as have the many other growers who also use this.
The master’s mix is 50% hardwood fuel pellets and 50% soybean hulls. These may sound like strange materials, but they’re actually not specialty items and can be found pretty easily.
The pellets are made from hardwood tree wood, often Oak or Maple, and processed into small pellets to be burned as fuel. However, they also make for a great Oyster mushroom substrate!
Soybean hulls are the hard shells around the bean that are usually discarded as agricultural by-products from processing soybeans, so using these is another way to reduce waste!
The wood pellets provide the right amount of moisture to the substrate while the soybean hulls create a rough texture that allows proper airflow and space for the mycelium to expand.
Whether or not you need to pasteurize these materials depends on what exactly you buy. The hardwood fuel pellets have already been processed so they’re definitely sterilized and ready for use. The question lies with the soybean hulls.
If you purchase soybean hulls in bulk from a gardening store, then there’s a good chance they’re already sterilized and ready, but you should still check the label to be sure. If you’re using soybean hulls from a local farmer- or even your own garden- then you absolutely need to pasteurize them.
This mixture was coined the Goat mix by the growers at Mossy Creek Mushrooms, who have tinkered with the Master’s Mix to create a substrate that works best for them.
Their Goat mix replaces the hardwood fuel pellets in the Master’s mix with straw pellets, so they use a substrate that’s 50% straw pellets and 50% soybean hulls. As I’ve explained, straw works super well for growing Oyster mushrooms, which is why the guys at Mossy Creek Mushrooms added some to their mixture.
They find that the texture with the straw pellets and soybean hulls really supports mycelium growth. They’ve shared that since using this substrate mixture, they’ve seen that the bags incubate faster and have increased yields.
You can certainly create an Oyster mushroom substrate using only straw pellets and this is what most growers do. That mixture is also easier since it’s just one ingredient and it’s sterilized, but the growers at Mossy Creek swear by their mixture using 50% soybean hulls, so it’s worth a mention!
Coco Coir + Vermiculite Substrate
This combination also works pretty well for growing Oyster mushrooms, plus it uses materials that you might already have for your garden. Coco coir and vermiculite are both super useful materials to add to potting mixes for plants that need a rougher soil mixture.
A mixture of 50% coco coir and 50% vermiculite works in a similar way that the Master’s mix works, by providing moisture and texture for aeration- the coco coir makes the mixture rougher and promotes airflow while the vermiculite retains moisture well.
This mixture isn’t as effective as growing on straw, but that’s not to say that it won’t work. You will likely get a smaller yield of mushrooms, but this can be a handy mixture if you already have these materials.
Coffee Grounds Substrate
An increasingly popular option for growing mushrooms, especially in urban areas, is to use coffee grounds for your Oyster mushroom substrate. Coffee grounds are another by-product that are often discarded, especially since you shouldn’t overload your compost with too much coffee at one time.
Many growers in cities will work with local coffee shops and use all their leftover coffee grounds to add to their substrate. Since straw works so well for Oyster mushrooms, many growers like to use 50% coffee grounds and 50% straw or straw pellets.
Coffee grounds add moisture and Nitrogen to the mixture, but they can be a bit tricky to work with. The most important thing when making an Oyster mushroom substrate with coffee grounds is to use fresh grounds and to break them up.
You need to use the coffee grounds within 24 hours of them being roasted, otherwise you risk mold developing which will contaminate your whole batch. It’s also important to thoroughly break up the clumps so that everything is loose enough to allow the mycelium to grow.
The growers that struggle when using coffee grounds have problems because they’re using only coffee grounds, which is too dense for the mycelium. Because coffee grounds are so finely ground up, they clump together easily and this is why you need to also use straw to keep the substrate texture open enough for airflow.
Aside from reducing food waste, one of the greatest benefits of using coffee grounds is that they get sterilized in the coffee making process, so this removes the pasteurization step.
The gills of pink Oyster mushrooms.
How to Grow Oyster Mushrooms
Now we can get into the step by step process for growing Oyster mushrooms! The overall process for growing mushrooms is pretty much the same regardless of what substrate you use, the only difference is whether you need to pasteurize or not.
To begin, there’s a few things that you’ll need:
- You’re chosen Oyster mushroom substrate
- Oyster mushroom spawn
- Large bucket or bin with a lid for mixing
- Grow bag or bucket
Some growers simply wash their hands before mixing and handling everything, so the gloves are optional but are a good precautionary step.
Since the spawn has to compete with other bacteria for nutrients to develop the mycelium, you want to make sure everything is as clean as possible, this will also decrease the chance of contamination.
If you’re not using a substrate that comes in pellets, it will either need to be sterilized or pasteurized to kill or reduce the number of organisms living in it.
Cleaning your substrate through the sterilization process is actually quite complex and requires specific equipment, so this method is only done by commercial growers.
Pasteurization, on the other hand, is very straightforward and can be done at home. The pasteurization process doesn’t kill 100% of the organisms living in the substrate material, however it kills most of those that will compete with the spawn.
To pasteurize your substrate, you’ll put it all in a water tight container and submerge in a water bath that’s around 160 F. It’s okay if the temperature fluctuates a bit, but you want the temperature to stay between 160 and 170F.
You need to leave the substrate in the water for at least 45 minutes up to one hour. Allow the substrate material to completely cool down before opening the container and combining with the spawn.
You’ll need to add water to your substrate so that there’s enough moisture to promote the spawn growing into mycelium.
Generally for Oyster mushroom substrates, it’s best to add 60% of the weight of the substrate in water. So, if you’re using 1 lb. of straw pellets, for example, you’ll add 9.6 ounces of water. If you’re using coffee grounds in the Oyster mushroom substrate, you don’t need additional moisture.
You can use room temperature water, just make sure it’s filtered. Pour into your mixing container with the substrate, mix well with your hands, then put the lid on the container. If you’re using pellets, try to break up the pellets a bit and make sure they’re all equally wet.
Adding the Spawn
After 30 minutes the water will be fully soaked in and you can add the spawn. For Oyster mushrooms, add 10% of the weight of the substrate.
After adding, break up the chunks of the spawn and mix the substrate well. Once you think everything is evenly mixed, it’s ready to go in the growing bag!
Filling the Growing Bag
You can use any bag or bucket as the holder for the substrate, as long as it’s completely clean. There are specific mushroom growing bags, but the only difference with these is that they’re longer so they can be hung up.
For beginner growers, it’s helpful to use a clear container so you can see the growth and know which step you’re at- plus, it’s super cool to watch the process!
When you fill the container, leave the top ⅓ open so that there’s excess air for healthy air exchange. Unless you’re using chopped straw as your mushroom substrate, in which case you can fill all the way to the top since it’s not so compact.
Once the bag is full make sure it’s properly sealed, and then wait for your bag to be inoculated!
You’ll want to leave the bag in a safe and stable place for the incubation period. The bag doesn’t need to be in the dark, but shouldn’t be in direct sunlight.
A room that’s 68 to 75 F is ideal, so most homes at room temperature are perfect. The inside of the bag will warm up as all the action happens and if the room warms up this increase will be exaggerated in the bag, so keep the bag in a room that won’t get too warm.
In about one week, you’ll see white spots in the bag, which is the sign that it’s inoculated! After another 1-2 weeks, it will be completely white as the mycelial network has spread all over the substrate. At this point, the fungi is ready to fruit!
A “mushroom coral” that formed because the bag was left in the dark for too long, so the mycelium didn’t receive enough sunlight and couldn’t form mushrooms. Oyster mushroom coral / Wendell Smith / CC 2.0
Take some scissors and cut an X towards the bottom of the bag or a hole in a bucket for the mushrooms to grow out of. If you’re growing in a bag, fold down the top of the bag so the mushrooms don’t try to grow inside the bag.
As with plants that you grow for their fruits, you want to create ideal conditions for the mushrooms to fruit. The best things you can do are provide light, humidity, and fresh air.
The mycelium doesn’t need light like plants do for photosynthesizing, but they will benefit from indirect light. Letting the mushroom container sit on a windowsill or near a window will help provide energy for fruiting.
You can provide humidity to the mycelium by misting the block a few times a day for several days until it begins to fruit. The mycelium just needs to be a bit moist, it doesn’t need to be watered!
The mycelium need some air circulation, but shouldn’t be placed outside where they can be exposed to other bacteria or fungi. The circulation in most vented rooms is enough for mushrooms, but if you notice that they’re a bit thin or weak, open the window just for a couple minutes to provide some air circulation.
The mushrooms will be ready for harvest about 2 weeks after creating the opening!
Harvesting the Oyster Mushrooms
How exciting! Just about one month after creating the substrate, the mushrooms will be ready for harvest and can be eaten right away.
For a home gardener, how awesome is it to start growing something and be able to harvest in one month! Plus, mushrooms are something you can grow all year round.
The ideal point for harvesting is when the tops are large but still rounded and haven’t flattened out yet.
Reach your hand underneath and grab the base of the mushroom cluster, twist, and pull it off the block. The mushrooms should come off very easily so if they don’t that’s a sign that they’re not ready yet and to wait another day.
Once you harvest, you can eat the mushrooms right away and store the mushrooms fresh in the fridge for about 10 days. You can also dry them in the oven or a dehydrator.
And that’s it! Creating and preparing an Oyster mushroom substrate is super easy and definitely something that anyone can do. Preparing the substrate is really the biggest effort in growing mushrooms, otherwise you just wait and watch them grow. Have fun with your fungi!
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.