Mushroom Substrate – A Comprehensive Guide to Mushroom Growing Medium
Topic of the day at the Garden Bench Top is mushroom substrate.
We answer all the important questions when it comes to choosing the best substrate for growing mushrooms.
- exploring the role of substrate in the mushroom growing cycle,
- the different types of mushroom substrates,
- specific mushroom substrate recipes for edible mushroom varieties, and
- frequently asked questions about the raw materials and organic matter.
What is Mushroom Substrate?
Put simply, mushroom substrate is the material that the mushroom spawn will use to attach itself and continue to grow to form the foundations of the mushroom colonies. It is sometimes referred to as a growing medium, and we use the two names interchangeably at the Garden Bench Top.
When you are creating your mushroom grow kits, the mushroom substrate will be the majority of the mixture.
The growth you see is known as the inoculation phase of the mushroom growth cycle. You will be able to recognize this stage because you will see thin white threads spreading all over the substrate, which can easily be mistaken for mold.
The mycelium uses the growing medium as a source for food and energy to quickly grow and begin fruiting. Therefore, as you can appreciate, it is an essential part of the growing mushroom process and should be well-considered before you jump into your mushroom farm adventures.
What is an ideal mushroom substrate?
Farmers in the mushroom industry use a large variety of mushroom substrate as a growing medium for their farms. This can range from straw, wood chips from hard woods, and mulch. Generally speaking, they prefer these types of substrate because they are cost-effective in large quantities.
Interestingly, house mushroom cultivators have been experimenting with other types of substrates, which we will discuss below. One reason we believe why they have been diverging from the norm, is because hobby mushroom farmers use smaller kits and can afford to use different organic materials. It may also be due to resource availability (or unavailability more to the point).
Below we will look at the usual substrates, as well as some other more unorthodox growing mediums.
Straw for Mushroom Substrate
Wheat Straw (or hay) is a very popular choice for a mushroom growing medium.
It is easy to handle and readily available – even in remote areas like farms. Another benefit wheat straw has going for it is that it can be purchased in bulk, and is affordable for the mushroom growing hobbyist.
What we love about straw is there are even some distributors that will sell pasteurized wheat straw, which can save you a tonne of waiting time and work when it comes to growing mushrooms. If you cannot find pasteurized straw, do not panic, because sterilizing the straw is an easy process that anyone one can DIY at home (we guide you through the steps of pasteurization below).
Wheat straw is great for growing the following varieties of mushrooms:
- oyster mushrooms,
- Magic Mushrooms (aka psilocybe cubensis), and
- Straw Mushrooms (aka Volvariella Volvacea).
Wood Chips Mushroom Substrate
Another popular substrate for home mushroom farmers is wood chips.
The thing about wood chips is you want to be particular about the type of wood you select. Generally speaking, you should be looking to avoid soft wood. So woods like conifer or pine wood shouldn’t be used, or if anything, should comprise a small portion of the overall mushroom growing bed.
Accessibility shouldn’t be a problem for wood chips, since it is usually a by-product of other product making processes. Which means you can usually pick it up for free (or extremely cheap). And if you are regular visitors to the Garden Bench Top, you will know we are huge advocates of anything to do with reinventing waste into a functional purpose.
You can also add in a bit of sawdust to the mix for a bit of variety. Since it will be from the same wood source, there is no risk of adding in any contaminants, and it will give the mushroom spores some easy nutrition.
Wood Chips is great of growing the following varieties of mushrooms:
- King Oyster,
- Lion’s Mane (aka yamabushitake),
- Reishi, and
Wood Pellet Mushroom Substrate
We thought it would be sensible to talk about wood pellets as another option for mushroom substrate.
Wood pellets can be used as a suitable substitute in replacement for wood chips. We thought it would be helpful to those who do not have access to wood chips.
You can usually purchase wood pellets at your local garden center at a reasonable price. We do recommend that you sterilize any materials you have purchased from garden centers. Given they deal with a huge range of plant material, it is easy for uninvited organisms to sneak into your mushroom growing kit.
Most of the mushrooms that grow on wood chips (above) will also grow with wood pellets.
Peat Moss Mushroom Substrate
Since we are all about the home gardener, we also wanted to include a few more off-the-beaten-path ideas that commercial farmers tend to overlook.
Peat moss is one of these mushroom substrates that we highly recommend. It is one of those substrates that seems to tick all the right boxes when it comes to creating the perfect cultivating environments for mushrooms.
One of the properties that is a must for mushrooms is access of water and humidity – something peat moss excels at as it can hold large amounts of water content.
Some home mushroom cultivators also like to mix different textured peat to encourage varying growth patterns in the mushroom growth cycle. In doing so, the mushrooms will fruit for longer periods of time and more consistently, rather than big flushes of mushrooms. This is ideal for DIY mushroom farmers, because you can leisurely enjoy fresh mushrooms for weeks, rather than just days.
Perlite Mushroom Substrate
Perlite is another one of those substrates that can be used to grow mushrooms. However, when used for large scale operations, can be quite costly and can easily be substituted for cheaper bulk materials.
Similar to peat moss, perlite has great water absorption capabilities, which means mushrooms will thrive, especially during the fruiting stages.
Generally speaking, gardeners use perlite as one (of many) components in their garden soil mixes. Which is something that you can apply to your mushroom kit mix recipe.
As a matter of fact, that leads us onto the next substrate – combination substrates.
Combination mushroom substrates
What you will find is most mushroom growers will include a few different types of growing mediums in their cultivation of mushrooms.
There are a few advantages of having a mix of substrates:
- greater nutritional value for the mushroom spores to consume, providing a better foundation for a success flush of mushrooms,
- easier to source and bulk out your mushroom growing kits. For example, if you can only source small amounts of straw, you can add waste coffee grounds or peat moss to bulk it out.
Below we will go through some popular substrate recipes for specific mushroom species.
Best type of substrate for specific mushroom varieties
If you have a particular species of mushroom that you are looking to grow in your backyard, you can tailor your substrate to enhance you chances of growing a successful crop of mushrooms. Below we have listed our favorite recipes for popular mushroom varieties.
Shiitake Mushroom Substrate Recipe
Our favorite recipe for growing shiitake mushrooms:
- 25 parts wood chips from a hardwood source (this will form the majority of your growing medium)
- 2 parts wheat bran supplement to provide nutrition for the spawn (this is only supplemental)
- 1 part gypsum or lime (provides calcium and sulfur which encourages healthy growth of mushrooms)
Reishi Mushroom Substrate Recipe
Our favorite recipe for growing reishi mushrooms:
- 25 parts wood chips/saw dust combination from a hard wood source (this will form the majority of your growing medium)
- 2 parts oat bran or wheat bran supplement to provide nutrition for the spawn (this is only supplemental)
- 1 part gypsum or lime (provides calcium and sulfur which encourages healthy growth of reishi mushrooms)
Portabello Mushroom Substrate Recipe
Our favorite recipe for growing portabello mushrooms:
- 25 parts pasteurized compost (ensure it is pasteurized to eliminate any unwanted guests)
- 25 parts pasteurized horse manure (ensure it is pasteurized to eliminate any unwanted guests)
- 1 part fresh soil (for creating a 1 cm layer on top of the mixture)
Oyster Mushroom Substrate Recipe
Our favorite recipe for growing oyster mushrooms:
- 25 parts fresh waste coffee grounds (must be at least within 24 hours from being made)
- 5 parts straw or hay (ensure it is pasteurized to eliminate any unwanted guests)
- 1 part mushroom spawn
Chestnut Mushroom Substrate Recipe
Our favorite recipe for growing Chestnut mushrooms:
- 25 parts wood chips/saw dust combination from a hard wood source (this will form the majority of your growing medium)
2 parts oat or wheat bran supplement to provide nutrition for the spawn (this is only supplemental)
1 part gypsum or lime (provides calcium and sulfur which encourages healthy growth of chestnut mushrooms)
Mushrooms Substrate Frequently Asked Questions
We get many emails from our readers asking for help when it comes to mushroom substrate. So we have decided to put together a neat little FAQ section that addresses a lot of queries that may crop up along your mushroom growing journey.
What do you do with Spent Mushroom Substrate?
Because mushrooms enjoy a moist environment, a lot of spent mushroom substrate is great for spreading in and around your garden for water retention purposes. It is almost like super charged mulch or top soil that helps to cultivate anything below the surface.
Some gardeners have suggested spreading it over the top of newly seeded lawn to help with germination, as well as protect prevent birds from feeding on the seed.
Due to the elevated levels of some nutrients that assist in the growth of mushooms, we also suggest ageing your spent mushroom substrate in an area of the garden, BEFORE spreading it around on your prized garden flora. We recommend allowing it to season for 6 – 8 months to be on the safe side.
Mushroom Yield per Pound of Substrate
It is natural to wonder how many mushrooms (or the yield of mushroom) you are going to harvest from your mushroom growing kits.
As a general rule we find for every 30 pounds (around 13 kilograms) of total mushroom substrate materials, you can expect to grow around 7.5 pounds (around 3 kilograms) yield of mushroom.
How to Pasteurize Mushroom Substrate
Pasteurizing is the process of sterilizing the mushroom substrate to eliminate any unwanted organisms or bacteria. You may be asking ‘Why do you need sterile mushroom substrate?‘
The main reason is to prevent bacteria or other plant organisms that your substrate may be housing from growing and eventually competing against your mushroom spawn.
You will be able to recognize if you have any intruders in your substrate with the appearance of mold. It is important to familiarize yourself with what mushroom mycelium looks like (picture below).
As you can see, it would be easy for a beginner mushroom farmer to mistake white mycelium for mold – and therefore discontinuing their journey based on a false dagnosis.
How to Pastuerize the Substrate?
There are several ways to pasteurize mushroom substrate. Many commercial mushroom farmers have large expensive pieces of equipment that can handle high pressure and extreme temperatures to sterilize bulk quantities of materials.
However, since the Garden Bench Top is designed for the home gardener, we will be focusing on budget friendly methods that is accessible to all levels of green thumbs.
The method we use (albeit rudimentary) is to essentially soak the substrate in a hot water bath. To achieve this, you will need a container that can withstand high temperatures. It also needs to be large enough to fit large amounts of bulk materials.
Simply To begin the sterilization process, simply place the materials into the container and submerge in hot water. The temperature should be close to boiling, although not hot enough to see a rolling boil.
We then recommend leaving the material to ferment overnight, and absorb approximately 70-90% water.
Hopefully by now you have a good idea of what type of mushroom substrate you are going to use for your mushroom grow kit.
The next natural step is to get your hands dirty with some DIY guides for “How to Grow Mushrooms at Home“. This guide will take you through the general process of the mushroom growth cycle, and how to construct your kit in a step-by-step process.