How To Choose And Prepare Mushroom Substrate

Mushrooms contain 70-90% water, and they draw every drop from their substrate. Substrate is the growing material (growing medium) used in cultivating mushrooms. Your mushroom substrate choice is a huge determiner for your cultivation success.

Growing mushrooms on a substrate is similar to growing plants in soil. The substrate provides all the nutrients for the mushroom mycelium to grow and produce mushrooms. Just as plants thrive in specific soils and conditions, different mushroom species prefer different substrates.

Straw, sawdust, coffee grounds, or manure – each substrate type offers unique benefits and challenges. And each mushroom species has its preferences. There is no one-size-fits-all substrate solution. The best mushroom substrate choice depends on which type of mushrooms you are growing and where and how you intend to grow them.

If you’re looking for substrate recipes, check out our guide, DIY Mushroom Substrate Recipes!

What Makes a Good Mushroom Substrate

A good mushroom substrate needs specific nutrients, precise moisture levels, and proper structure to help mycelium grow healthy. The quality of the mushroom substrate depends on its nutrient mix. Most substrates contain nutrients naturally, so you don’t need to add anything additional. Some benefit from supplementation with other organic materials to create a perfect growing medium.

The substrate should contain carbohydrates, proteins, lipids, vitamins, and minerals that support cell growth and repair. The nitrogen content should stay between 1-2%. The mushrooms also need small amounts of magnesium, potassium, calcium, sulfur, and phosphorus to maintain metabolic processes. And, the substrate’s pH should remain slightly acidic between 5-6.5, though oyster mushrooms can handle levels up to pH 8.

The mushroom substrate needs 50-70% water to hydrate the mycelium properly. Different mushroom types have different moisture needs. For example, oyster mushrooms prefer 60% moisture, while shiitake mushrooms do better at 50-55%. When you squeeze your substrate, it should feel like a wrung-out sponge and hold together without dripping.

The substrate needs a structure that lets oxygen flow freely so mycelium can colonize. On top of that, it should resist compacting to avoid anaerobic zones that stop growth. A well-laid-out substrate helps mycelium spread through the material. The goal is to make it easy for the mycelium to spread so it can reach all the nutrients. This is how you get strong, beautiful mushroom flushes.

The importance of a clean workspace:

A clean workspace is necessary for successful mushroom growth. Contamination from bacteria, molds, and other fungi can easily ruin your grows. To prevent this, keep your environment sterile at all times. Cleanliness helps stop unwanted organisms from affecting mushroom growth. This applies throughout the entire process, from preparing the substrate to harvesting the mushrooms. Wiping down surfaces with 70% isopropyl alcohol is generally sufficient for the home grower.

A tidy environment also makes it easier to spot potential problems early, like contamination or pests. Keeping tools and materials organized lowers the risk of cross-contamination during different stages of cultivation.

Long-time mushroom growers and commercial operations usually have intensive cleanliness standards, including separate sterile rooms for inoculation. For the home grower, though, this usually isn’t possible. And it isn’t entirely necessary, either.

Common Types of Mushroom Substrates

The mushroom species you want to grow determines your choice of growing medium. Each type of substrate has its benefits and potential downsides.

The most economical approach is to use pasteurized mushroom substrates without supplements (though this may affect your yields). Cultivation success depends on matching your substrate with materials you can find locally and what your specific mushroom species needs.

Straw

Straw is one of the most budget-friendly and easy-to-find substrates. You’ll get the best results with wheat or oat straw. Straw is widely available, inexpensive, and easy to work with. Straw provides excellent aeration and moisture retention, which are crucial for mushroom growth. The hollow structure of straw allows for good mycelium colonization.

However, straw can be less nutrient-dense compared to some other substrates, which may result in slightly lower yields. Pasteurization is also required to eliminate competing organisms. Cut the straw into 1-3 inch pieces to get good results.

Mushroom Types: This mushroom substrate works great with oyster mushrooms – blue, pink, yellow, pearl, and king varieties all thrive on it. Shiitake, wine caps, enoki, and Pioppino mushrooms also do well on straw or straw mixes.

Sawdust

Hardwood sawdust is an excellent growing medium, especially from oak, maple, beech, and hickory trees. Sawdust provides a good balance of nutrients and structure. It’s particularly effective when supplemented with bran or other nitrogen sources. The downside of sawdust is that it can be more challenging to obtain in large quantities for home growers and requires proper sterilization to prevent contamination.

You should mix sawdust with wood chips to help colonize faster and create a better mycelial structure. The choice of specific hardwood can affect the growth rate and yield.

Sawdust or wood chips are economical solutions, and local woodworking shops or lumber mills often give them away for free. Many hardwood varieties work well, which gives you flexibility in sourcing materials. The best approach is to check with nearby carpentry workshops for sawdust. Make sure the wood comes from suitable hardwood species. You can mix different hardwood varieties to optimize growth conditions.

Mushroom Types: Several types of mushrooms grow well in hardwood sawdust, including Shiitake, oysters (various), Lion’s mane (beech, maple, oak), Maitake (oak), Reishi (oak and maple), Nameko (beech)

Hardwood Pellets

Hardwood fuel pellets are a great alternative if you can’t get sawdust easily. These pellets are simple to use and have consistent moisture content, which makes them perfect for beginners.

Hardwood chips or wood pellets provide a long-lasting mushroom substrate with good structure and nutrition. Wood pellets, in particular, are convenient as they expand when hydrated, creating an ideal growing medium. The main drawback is that they may require longer colonization times than softer substrates like straw. This means it might take 4-6 weeks to be able to harvest instead of 2-3 weeks.

They work with all the same species you can use for hardwood sawdust.

Wood Chips

Wood chips are a great choice for growing mushrooms. They create a natural environment that helps mushrooms that grow on wood thrive. Wood chips are also easy to find and often low-cost or free from tree services or landscaping companies. They retain moisture well and allow for good air circulation, which lowers the risk of contamination and helps mushrooms grow evenly.

Using wood chips for growing mushrooms has some drawbacks. One major issue is that it takes a long time for the mushrooms to colonize the wood. This process can take several months. The type of wood is also important; some woods have natural chemicals that can stop mushroom growth, so choosing the right wood is necessary.

Mushroom Types: Oyster, Shiitake, Lion’s mane, Wine cap, and Almond agaricus

Manure

There are three primary manure-based substrates: cow, horse, and sheep. Manure is a nutrient-rich material that helps mushrooms grow well because it has lots of nitrogen and other important elements. This natural fertilizer encourages strong mycelial growth, which can lead to higher yields. Using manure as a growing medium is also eco-friendly because it recycles waste from livestock farming.

Using manure for growing mushrooms has some drawbacks. The main issue is contamination. Manure can contain harmful bacteria, parasites, or other fungi if it isn’t properly composted or sterilized. This means you need to prepare and monitor the substrate very carefully. Also, of course, manure has a strong smell, which can be unpleasant, especially in small spaces.

Properly handling and processing manure is essential. First, age and compost the manure before using it. Next, pasteurize it to eliminate unwanted organisms. This creates a clean environment for spores to grow. You can also purchase pre-sterilized manure so you don’t have to deal with it yourself.

Mushroom Types: Button, Almond Agaricus

Soy Bean Hulls

Soybean hulls are a leftover product from processing soybeans. They are easy to find and make a sustainable and cost-effective choice for mushroom farming. One advantage of using soybean hulls is that they are rich in nutrients. This can help mushrooms grow faster and may lead to higher yields than other materials.

Using soybean hulls as a mushroom substrate has some drawbacks. They can be very dense, so it is usually necessary to mix them with a bulking agent like sawdust or straw to help improve air circulation.

Soybean hulls may also hold too much water, which can create low-oxygen conditions. This will slow down mycelial growth or lead to contamination. To avoid this problem, monitor and adjust the moisture levels carefully during cultivation.

Soybean hulls are rich in nutrients, but this can make them more vulnerable to harmful organisms. It is important to use proper sterilization methods to avoid contamination. Many growers agree that the advantages of using soybean hulls are greater than the possible issues as long as they are adequately managed.

Mushroom Types: Oyster, Shiitake

Logs

Growing mushrooms on logs is a simple and natural method with many benefits. This technique mimics the natural conditions where mushrooms grow, often leading to tastier and higher-quality fungi. Log cultivation is also good for the environment because it uses waste wood and needs little energy. Also, logs can produce mushrooms for several years, which means a long-lasting yield with low maintenance once they are set up.

Growing mushrooms on logs has some downsides. It can take a long time, usually several months to a year, before you can harvest anything. This method also needs more space and requires a lot of work at the beginning. Weather can affect outdoor log growing, making it less reliable than growing mushrooms indoors. Finally, you can grow fewer types of mushrooms on logs compared to other methods.

Logs make an excellent long-term investment in mushroom cultivation. Though the original setup costs more, you get extended harvesting periods and added value from unused wood species.

Around 3.5 feet long and around 15cm in diameter are the ideal log size for growing mushrooms.

Mushroom Types: Oyster, Shiitake, Lion’sLion’s Mane, Hen of the Woods (Maitake), Reishi, Wood Ear

Coco Coir

Coco Coir comes from coconut husks and has many benefits for growing mushrooms. It retains water well, which keeps moisture levels steady for mushroom growth. This material is also eco-friendly, as it is renewable and biodegradable. Coco Coir is naturally resistant to contaminants, which lowers the chance of mold or bacteria developing. Plus, it has a neutral pH, making it suitable for many types of mushrooms.

Coco Coir has some drawbacks. It can be more expensive than other substrates. Coco Coir can also become compacted over time, reducing air circulation in the substrate. Additionally, it contains fewer nutrients than some other growing mediums, so you need to add extra nutrients or substrate material for the best mushroom growth. This one is rarely used on its own.

Mushroom Types: Oysters, Button Mushrooms

Coffee Grounds

Used coffee grounds are great for growing mushrooms sustainably. The brewing process sterilizes the grounds naturally so that you won’t need extra sterilization. Make sure to use the grounds within 24 hours after brewing. This mushroom substrate works best when you mix it with 20% straw to improve air exchange.

Coffee grounds are a green substrate choice that saves money and helps the environment. The coffee bean biomass would go to waste otherwise. Urban growers have increasingly taken to coffee grounds because their rich nitrogen content works perfectly for oyster varieties.

Mushroom Types: Oysters, Reishi

Paper and Cardboard

Paper-based substrates are an eco-friendly way to grow mushrooms. Waste paper contains cellulose and hemicellulose that help mushrooms grow well. Adding corn stalk and wheat bran makes this substrate even more effective.

Cardboard serves as another cost-saving growing medium that often costs nothing. This light material supports various mushroom species and, as a bonus, is a great way to recycle cardboard!

Mushroom Types: Oysters

Mushroom Substrate Supplements Options

Substrate supplements are nutritional additions that improve mushroom growth and yield. These additions provide key nutrients and create a better substrate structure so mycelium can develop well.

Bran, oats, vermiculate, or hemp hulls provide valuable food sources for the growing mushrooms. Adding any of these enriches the substrate with carbohydrates, proteins, and minerals. In the preparation of the mushroom substrate, these are mixed with other materials such as sawdust, straw, or wood chips. Other common supplements include gypsum, which improves the substrate structure while adding calcium and sulfur.

Too many supplements can cause microbes to compete and spoil the substrate. Each mushroom species needs different nutrients, so pick supplements that match what you’re growing. How you make your final mushroom substrate will significantly affect yield and mushroom quality.

Not everyone uses these enhancements, and most people don’t use them all at once. Growers have their preferences based on their setup and mushroom strain. This is an area for experimentation to determine which supplements work best for which species and how much.

How to Choose the Right Mushroom Substrate

Different mushroom types need specific substrates that boost their growth and yield. Your substrate’s final mix affects your mushroom’s flavor and texture. The right growing conditions come from matching each species to its ideal substrate.

• Button mushrooms do best in composted substrates mixed with straw and manure.
• Shiitake mushrooms grow best on hardwood sawdust from oak and beech or growing from logs outdoors.
• Oyster mushrooms grow well in many substrates – from straw to wood chips to coffee grounds.
• Lion’s mane mushrooms grow well on hardwood sawdust, especially when it comes from oak, beech, or maple trees.
• Reishi mushrooms like hardwood sawdust with added nutrients like rice bran or wheat bran.
• Hen of the Woods does best on hardwood sawdust or growing from logs.

Your mushroom substrate choice will probably reflect what’s available and affordable. Straw makes an economical choice since farmers often have it as a byproduct. The lumber industry’s waste, wood chips, and sawdust are also affordable options.

The best results come from matching your substrate to both the species’ needs and what you can easily get. Oak and hard maple substrates pack dense nutrients and fruit longer. Soft hardwoods like poplar grow faster but give smaller yields over time. This trade-off between quick results and total production should guide your mushroom substrate choice.

You’ll notice we don’t say exactly what substrate or substrate mix to use, and this is because there is no one way or one answer. Here, we have some mushroom substrate recipes written out along with the suggested species to grow on them. But, other than that, there is a lot of room for experimenting and finding the right mix for the mushrooms you are growing. If you ask any mushroom farmer what they use, they’ll all probably tell you a different mix!

Tips For Preparing Your Mushroom Substrate

• Good substrate preparation starts with the right sizing. Cut straw-based substrates into 2-5 inches long pieces. This gives more surface area for mycelium to grow.
• Hardwood sawdust works best when mixed with wood chips. This creates the perfect structure for mycelial growth.
• The right supplements can increase your mushroom yields. Add bran or seed products at a ratio of 5-10% of the dry weight.
• Getting the correct moisture content is crucial. Most substrates need moisture levels between 60-65%. You can use the squeeze test to check this—your substrate should stick together without dripping water.
• Soak straw substrates well until they are evenly damp. This helps the moisture spread throughout the material.

Step by Step Substrate Preparation

A well-prepared mushroom substrate gives your mycelium the nutrients it needs while staying structurally sound.

1. Prep the substrate material.
   • You should cut the straw into 2-5 inches to create optimal surface area. This specific sizing makes mycelium colonization better. It also makes it easier to handle the material.
   • If you’re using hardwood pellets, soak them overnight to break them down.
   • Manure-based substrates require proper composting before use. This process usually takes several weeks, and you must turn the material regularly for even decomposition. Or you can buy pre-sterilized manure.
2. Pasteurize or sterilize the substrate as needed.
   • Nutrient-rich materials like supplemented sawdust need pressure cooking at 120°C for 2 hours.
   • Less nutritious substrates, like straw, need pasteurization at temperatures between 60-80°C for 1-2 hours.
3. Keep your prepared substrate in a clean environment, free from contamination, until you’re ready to use it.

Pasteurization vs Sterilization

Pasteurization and sterilization are two distinct processes used in mushroom cultivation to prepare substrates and reduce contamination risks. You don’t always need to sterilize or pasteurize the mushroom substrate. Doing this can reduce the risk of contamination and related growth problems, though. Some mushrooms cannot grow on sterile media and must be cultivated outdoors or in rich nutrient environments where sterilization isn’t possible.

Sterilization, on the other hand, is a more thorough process that eliminates all living microorganisms, including spores, from the substrate. It typically involves using an autoclave or pressure cooker to heat the substrate to temperatures above 121°C (250°F) under high pressure for extended periods, often 60-90 minutes or more. Sterilization is necessary for substrates that are nutrient-rich and prone to contamination, such as grains or sawdust-based substrates.

The substrate type determines which method you should use. Substrates with low nitrogen content are pasteurized, while nutrient-rich materials need complete sterilization. Manure, rye grain, popcorn, brown rice, and wheat berries must be sterilized. They are high in nutrients, which attracts many types of fungi and mold.

Chemical sterilization options

Chemical disinfection is an economical solution compared to traditional heat treatments. Chlorine dioxide (ClO2) is a powerful oxidizing agent that kills bacteria and fungi effectively. This compound is safe for humans and the environment. Using chemical disinfection is effective and a great option, especially in rural areas with limited resources.

How To Sterilize Mushroom Substrate

Steam sterilization heats the substrate with high-pressure steam in an autoclave or large pressure cooker. You need to heat the substrate to 121°C (250°F) for about 60 to 90 minutes. The time depends on the amount and density of the material.

Substrate mass determines the sterilization duration. A load of 40-45 lbs. needs at least 3 hours at pressure. Smaller quantities take less time. The PSI must be at 15 throughout the sterilization cycle. The process has three phases: a heating cycle of 10-60 minutes, a sterilization cycle of 15 minutes to 3 hours, and a cooling period of 1-24 hours.

Pre-soaked mushroom substrates create internal steam when heated, which boosts the sterilization process. The steam must touch the substrate directly instead of being underwater. Submerged materials might not reach the proper sterilization temperatures.

Most beginners use pressure cookers. Pressure canners are a middle-ground option with more capacity than pressure cookers.

Step-by-step guide to sterilizing substrate for mushroom cultivation:

• Soak the substrate for 24 hours before sterilizing.
• Prepare the substrate by mixing in any necessary supplements (e.g., gypsum, bran).
• Fill sterilizable bags or jars with the prepared substrate. Leave some space at the top for expansion during sterilization.
• Seal the containers, leaving a small opening for steam to escape
• Use a pressure cooker or autoclave (follow the manufacturer’s instructions). Make sure to place a rack or trivet at the bottom to keep containers off the water.
• Carefully place the substrate-filled containers in the pressure cooker. Ensure they’re not touching the water directly.
• Heat until it reaches 15 PSI (pounds per square inch). Maintain pressure and temperature for the required time:
  • Sawdust or straw: 1.5 to 2 hours
  • Grain: 2 to 2.5 hours
• Turn off the heat and allow the pressure cooker to cool naturally. Do not attempt to open until pressure has fully released (usually 5-6 hours).
• Once cooled, carefully remove the sterilized substrate containers.
• Store in a clean area until ready for inoculation.
• Use within 24-48 hours for best results.

Remember, maintaining sterile conditions throughout the process is crucial to prevent contamination.

How To Pasteurize Mushroom Substrate

Pasteurization is a gentle heat treatment used for certain materials. It involves heating the substrate to about 65-82°C (150-180°F) for several hours. Although it doesn’t eliminate all microorganisms like full sterilization does, pasteurization can effectively keep helpful microorganisms that you may want to maintain.

Step-by-step guide to pasteurizing substrate for mushroom cultivation:

1. Chop or break down the substrate into smaller pieces if necessary.
2. Fill a large pot or drum with water, leaving enough space for the substrate.
3. Place a thermometer in the water to monitor the temperature.
4. Bring water to a boil. Turn it down until it’s in the desired temperature range, 65-71°C (149-160°F).
5. When the water is at the right temperature, add your substrate to the hot water. You can put it in loose or in an old pillowcase or mesh bag. Using a net bag for chopped straw makes it easier to remove and drain later.
6. Place a weight on top of the substrate to keep it underwater.
7. Keep the water at the right temperature and submerge the substrate for about two hours.
8. Stir occasionally to ensure the heat spreads evenly.
9. When the time is up, turn off the heat and let the substrate cool down. If you put the substrate directly into water, wait for the water to cool before taking it out and squeezing out any extra water. If you used a pillowcase or bag, take it out of the hot water and hang it up to drain and cool.
10. To cool the substrate faster, remove it from the bag after it has drained and spread it out on a clean surface.

Remember to maintain proper hygiene and sterile conditions throughout the process to prevent contamination.

Quick Straw Pasteurization Method:

Put your mushroom substrate mix into a heat-resistant bag and fill the bag with boiling water until the mix is submerged. Carefully seal the bag and let it sit for up to 8 hours or until it cools completely. Once it’s cool, cut the bottom corners of the bag to drain the water.

Testing Mushroom Substrate Quality

Your substrate’s moisture should be between 50-70%. A quick test is to squeeze a handful – it should stick together without dripping water.

The substrate needs the right pH levels. The sweet spot is between 6.0-6.5. pH strips or digital meters work well for testing. You can adjust the pH level with gypsum or lime as needed. pH levels affect how nutrients become available and how enzymes work during nutrient absorption.

Check your substrate to see if supplements are mixed well and spot any problems. The color should be even, and the texture should be consistent throughout. A good mushroom substrate keeps its shape without getting too packed, which lets oxygen flow freely for mycelial growth.

Look at the substrate’s color throughout the entire growth time to ensure there is good distribution and structure for proper air exchange. Keep an eye out for contamination signs like odd discoloration or bad smells. A good mushroom substrate looks uniform without any clumps or dry spots.

Common Substrate Problems

Signs of contamination

Contamination causes the most failures in mushroom cultivation. Look for discoloration – green, blue, gray, or black patches usually mean mold has appeared. Strange odors, especially sour or musty smells, point to bacterial contamination. You might also notice slimy patches or too much wetness that indicates bacterial problems called “wet spots” or “sour rot.”

Moisture issues

The correct moisture balance plays a vital role in substrate performance. Low moisture slows down growth and makes the substrate shrink and compact. Too much moisture creates soft, mushy mushroom caps and raises contamination risks. Your mushroom substrate should feel damp and release just a few drops when you squeeze it.

Poor colonization fixes

Mycelium growth can sometimes slow down or stop, but several solutions can restart the process. Moving your growing container to a space between 18-24°C helps wake up stalled mycelium. Poor colonization usually happens because of low spawn rates or wrong temperature settings.

To fix colonization problems:

• Keep your substrate loose to allow proper airflow
• Keep room temperature steady and avoid direct sunlight
• Add enough spawn to get fast and reliable colonization
• Small contamination spots (coin-sized) can be removed with clean tools. But if contamination spreads too much, you must isolate the substrate immediately to protect other growing areas.

Common Questions About Mushroom Substrates