GROWING MUSHROOMS ON SAWDUST BLOCKS

ON THIS PAGE (Click to skip to sections):

- Introduction

- Substrate Mixes

- Preparing Substrate

- Sterilising Substrate / Steaming Substrate

- Inoculating Sawdust Blocks

- Incubation

- Fruiting

- Species Notes

Growing mushrooms on sawdust blocks is the best way to grow consistent crops of a wide variety of gourmet and medicinal fungi. It is a more advanced method than growing on straw or preparing logs, and requires some extra equipment and experience, but it will also open the doors to a wider range of options in terms of species that you can grow. 

SUITABLE SPECIES: 
The following species are suited to the methods described on this page, and are species which are permitted to be grown here in New Zealand. You can buy cultures or pre-prepared grain spawn of these species right here on this site

  • Shiitake (Lentinula edodes)

  • NZ Shiitake (Lentinula novae-zealandiae)

  • Pekepeke-kiore / Coral Tooth / NZ Lions Mane (Hericium novae-zealandiae)

  • Enoki (Flammulina velutipes)

  • Tawaka / Poplar Mushroom (Cyclocybe parasitica)

  • Oyster Mushrooms (Pleurotus species)

  • Turkey Tail (Trametes versicolor)

Introduction

Growing mushrooms indoors on sawdust blocks is a great method to grow wood loving species of mushrooms, with a quicker yield and more consistency than outdoor log cultivation, which can take a year or more to produce a crop and depends on the whims of the weather conditions at the time. Whereas blocks can begin fruiting in as little as a few weeks. Sawdust block cultivation is the primary method of production used by small to large scale commercial growers of gourmet and medicinal mushrooms asides from button mushrooms which grow on compost. 

The goal of sawdust block cultivation is to provide a good substrate for the mycelium to grow on. This is generally comprised of sawdust or fine wood chip, mixed with an additional (optional) nutrient supplement like wheat bran or soy hulls. The substrate mixture is hydrated, sterilised, and then inoculated with grain spawn or liquid culture of the desired mushroom species, before being incubated until it is fully colonised, at which point the sawdust can be put into fruiting conditions to grow mushrooms! 

 
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Substrate Mixes

Wood loving mushrooms can be grown on blocks of plain sawdust, but they're often supplemented with an additional source of nutrient such as bran or hulls of various types of seeds. 

INGREDIENTS 
1) Sawdust or fine woodchip. This can be purchased, or ‘home made’. The key thing about the wood material is that it is clean, fresh, and free of excess bark and leaves. As a rule of thumb, hardwoods are preferred, although success has been had on pine as well. A common choice of substrate is compressed firewood pellets or blocks. BioBriqs (www.biobriq.nz) are made from sustainably harvested New Zealand native beech, and work great. Also, the likes of Mitre 10 etc often have singular tree species (Oak, Maple etc) hardwood fire pellets, usually in the BBQ section. 

2) Nutrient supplements. Nutrient supplements are optional. They increase yield by boosting nutrients, but these extra nutrients also increase the risks of contamination. These mushrooms will grow on plain sawdust or fine woodchips. However most experienced growers choose to add supplement. Common supplements include wheat bran, soy hulls, lucerne chaff, oats or hemp hulls. There are many more things that you can use – and feel free to experiment!

3) Filter patch bags. Purpose made mushroom growing bags are the container of choice to hold substrate. They are food grade, autoclavable (heat resistant), and have a specially made porous filter built into the bag, which allows for air exchange so that the mycelium can breathe, while keeping out potential contaminants like mold spores or bacteria. Available from www.mycologic.nz

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Options for Substrate Mixes

 

PLAIN
If you do not have access to a pressure cooker or a very sanitary area for making your bags (such as a ‘still air box’ or HEPA flow hood work space), starting with plain, unsupplemented sawdust or fine woodchip can be a smart option. Grain spawn is itself a good nutrient source, so if using plain wood substrate, using a higher spawn rate can be equally as good at boosting nutrients in the block, and also makes for quick colonisation, thus further reducing the chances of contamination. 

WHEAT BRAN 
Wheat bran is a popular choice of supplement for mushroom blocks, especially among ‘old school’ growers. I like it because it is cheap, easy to find, and it is grown here in New Zealand so has not travelled too far. It can be obtained in small amounts from bulk food stores or supermarkets, or in big bags from farm supply outlets. 

Wheat bran should be used at a rate of 10 to 20% of the dry weight of the substrate, before water is added, with the rest being sawdust or fine woodchip. 

MASTERS MIX
The so-called masters mix has become a popular substrate choice in recent years. It is a mega-supplemented, nutrient loaded mix which consists of a 50/50 mix of soy hulls and sawdust (by dry weight before water is added). Soy hulls can be purchased from farm supply outlets. One brand name commonly seen is called ‘maxisoy’. 

FREESTYLE CREATIVE
Variations of the above mixes can be experimented with, using alternate supplements like various chaffs or seed hulls.

Preparing Substrate
 

The basic process of preparing substrate has some simple goals – hydrate the substrate evenly and to the correct amount, mix it well, and load it into your growing container (e.g. filter patch bag). 

The first step is to properly hydrate the substrate. As a rule of thumb, normally for every 1 part of dry substrate (by weight), 1.5 to 1.8 parts of water is added. This varies depending on the substrate, how dry it is, how absorbent it is and so on. Essentially, the key goal is to achieve field capacity moisture levels in the substrate. 

Notes on Field Capacity
Personally, I rarely actually weigh or measure my substrates these days. And that is because once you get the hang of it it, it is fairly easy to get the right moisture content just by feel.

 

Field capacity basically means the amount of water / moisture that a material will naturally hold, without having excess. 

The easiest way to test this, is after the substrate has been left to sit for a while, and mixed a few times to hydrate evenly, pick up a handful and do the squeeze test

If you squeeze a handful of substrate and water comes out – even just a drop or two – then it is too wet, and a small amount of dry substrate should be mixed in to adjust. If you squeeze it and it feels like some water is about to drop out, but doesn’t, that is the perfect field capacity. If the substrate feels or looks dry like weetbix, some extra water can be added slowly and sparingly, with mixing, until the right moisture level is reached. 

This same rule applies no matter what your specific substrate mix is.

Hydrating

In a large tote bin or similar, add the sawdust, and any supplements you have chosen to make your substrate mix. Measure out some water approx 1.5 to 1.7 times the weight of the dry substrate.

 

Mixing

A sturdy plastic scoop is handy for both mixing, and loading the substrate into bags. Mix the substrate, and test for field capacity of moisture (see previous section). Adjust moisture level accordingly.

 

Bagging

Once the appropriate moisture level (field capacity) is reached, and the substrate thoroughly mixed, it can be put into filter patch bags. Bags should be filled about half way or just over. Tamp down on a bench to slightly compress the mix.

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Sterilising Substrate

After filling the bags with the prepared substrate of choice, they must be thoroughly sterilised prior to being inoculated with spawn. This is to kill off unwanted contaminants and pathogens such as molds and bacteria.

 

Ideally, the filled bags of substrate will be pressure cooked at 15 PSI for 60 to 90 minutes. To do this, simply load the bags into the pressure cooker (with a rack in the bottom to hold the bags off the hot metal base of the pot), and add a couple of centimetres of water in the bottom.

 

Then, with the steam vent open, bring the cooker up to boiling temperature (when some steam start coming through the vent), before closing the steam vent (or adding the weight). Wait for the cooker to reach 15 PSI, then hold it at 15 PSI for 60-90 minutes, then turn off the heat and allow the pressure cooker to naturally cool (without opening the steam vent or weight) for at least 6 to 8 hours. Bigger loads require longer cooling time (12+ hours).

Ultra Pasteurising / Steaming

If you do not have a pressure cooker, you can instead ‘ultra pasteurise’ your substrate by steaming it for several hours in a large pot or similar vessel. Technically, this is not ‘sterilisation’, but in most cases, it is enough to do the job.

 

The process of ‘ultra pasteurisation’ (prolonged steaming) is fairly simple, and similar to pressure cooking in its methodology, just done for a longer amount of time.

 

The first step is to find a large metal vessel that can withstand being heated for a long time. Large stainless steel stock pots work well, or, if you have access to one, an old 50L beer keg with a circular hole cut in the top to fit a lid, works great, although requires a gas burner as it will not fit on an electric stove.

Like most things, there is more than one way to skin a cat, and ultra pasteurising / steaming substrate is no exception. Described below is an ultra basic approach that works well. It can be improved and modified in many different ways depending on scale, and what materials you have on hand.

 

In this example, an old beer keg is used, which has had a circle cut out of the top with an angle grinder, to fit a large pot lid found at the local dump shop.

 

1. Creating a spacer rack.

There needs to be something in place to hold the bags off the bottom of the pot, to prevent them from burning / melting and hold them above the boiling water. In this case, I have used an upside-down flat based metal colander, with some other random perforated metal discs on top of that to make a platform. This can be improvised in any number of ways but something that can hold bags 5 to 10cm or more above the bottom of the pot is what you need.

2. Folding the bags.

This seems like an inconsequential step but it is in fact quite important. If you have filled your bags 1/2 to 2/3 full as recommended, there will be enough surplus bag at the top to fold it over. Make sure that you fold the bag so that the filter patch is covered (on the inside of the fold) so that it remains dry during the steaming process.


3. Loading the pot and steaming.

Plenty of water should be added to the pot, before loading it. The last thing that you want is for the pot to boil dry during steaming. You can top it up with more hot water part way through the process if you think that it might run dry. In the case of this beer keg, I have added approx 10cm deep of water (so, about 5-8 litres) in the bottom prior to adding the bags. Extra water can be added during the process if you're worried that its running low.

 

The bags should be loaded in neatly, so that they support one another and are not loose, and so that the flaps of the folded tops are held secure by other bags.

 

Once the pot is loaded up, it can be put on the heat, either on an electric element or a gas burner, depending on the size of the pot. Make sure that the vessel is stable and secure, and that this is done in a ventilated area. Safety First! 

 

The lid should be put on as soon as the pot is put on the heat. This is to keep the warmth and steam inside the vessel. I often place a heavy object on top of the lid, like a rock, to hold the steam in and stop the lid from rattling around.

 

Once the pot comes to the boil, the heat of the element or gas burner can usually be reduced, to about medium. Enough to keep the water going at a rolling simmer.

 

From here, the steaming process needs to continue for a few hours. Some folks who steam substrate, do it for up to 24 hours. Personally, I have found that around 4 to 5 hours usually does the trick.

 

After steaming, the blocks take a long time to cool. Turn the heat off and leave the lid on the pot at least overnight. 

 
 
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Inoculating Substrate

 

Whether you pressure cooked or ultra pasteurised, you will now have filter patch bags full of sterile substrate, ready to inoculate with grain spawn.

 

It is important that inoculation is done in a clean area. Whether this is a kitchen bench that has been well spritzed down with 70% alcohol / meths / isopropyl, and generally clean environment (this is an absolute bare minimum), through to a ‘Still Air Box’ (google for more info) or of course the ideal, a HEPA filtered work space. Basically, you need to create the cleanest work area that you can, to prevent contamination of your substrate by airborne microbes during the inoculation step.

 

To inoculate the substrate, open your pressure cooker or steamer vessel in your clean area (after it has cooled for 12ish hours). Depending on the size of your workspace you may have to go one bag at a time (e.g in a still air box).

Unload a bag from your pot, into your workspace. Have your bag of grain spawn ready. Some people spritz the outside of the grain spawn bag with alcohol spray. But at the very least, cut it open with sanitised scissors.

 

Its important to work quickly, but gently. Wear freshly washed clothes. Wash your hands well and use hand sanitiser (again, alcohol spritz from a spray bottle works well). Avoid creating air disturbance. And keep your spawn, and substrate bags, exposed to the outside air for as short of a time as you can.

 

To inoculate the bags, open up the substrate bag from the top, and pour in some broken up grain spawn. As a rule of thumb, spawn is added at 5 to 10% of the weight of the block. So for a 2.5kg block, 125 to 250g of spawn is normally added. After inoculation, place the grain spawn bag in a clean area (or seal it back up) and then seal your substrate bag as well.

Ideally, an impulse sealer (heat sealer) is used to seal up the top of the substrate bag. Some domestic vacuum sealers also have a heat sealer built in that you can use. Alternatively, you can twist the very top of the bag, fold it over once (to improve the seal) and then cable tie it closed.

Now that the bag is sealed, the spawn needs to be mixed through the substrate as evenly as possible. This is one reason for leaving plenty of empty space in the bag. One good way is to press an indented ‘channel’ down the length of the bag, then shake the grain spawn down the channel from the top of the bag to the bottom. From here, the bag can be rolled / massaged to continue to mix the spawn through. Once the spawn is well mixed, the substrate should be ‘tamped’ down on a bench top, back into a solid block.

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Incubation

After the blocks are inoculated, they’re ready for incubation. This is a pretty simple step. Put the blocks into a clean container such as a lidded tote bin / storage box, and incubate them at around 18 to 25°C while the mycelium spreads off the grain spawn and grows throughout the substrate. 

Incubation times vary between species, spawn rate, temperateure etc. Some rough outlines are:

- Oyster Mushrooms 1-2 weeks 

- Enoki, Tawaka, Hericium, Turkey Tail 2-4 weeks

- Shiitake including NZ Shiitake 3-4 months, until substrate has formed a bumpy 'skin' (called popcorning) and / or turned brown on the outside. 

As per usual, keep an eye out for contaminants. Anything other than fine, white mycelium could be a bad sign. If spots of blue or green (or other coloured) molds, or blotches of gooey bacteria emerge, then the block is contaminated and should likely be discarded.

 

Once the block is fully colonised, it is ready to be put into fruiting conditions.

Fruiting Mushrooms

Once your blocks are fully colonised with mycelium, they're ready to fruit. Fruiting areas can vary massively in their size and level of complexity. Anything from popping a block under some tomato plants in a humid greenhouse, to a basic home made fruiting chamber in a large tote bin or a 'mini greenhouse', through to a high tech fruiting room with all the bells and whistles, there are a few key features you're aiming for with a fruiting space. These are: 

HUMIDITY: The optimal humidity for mushrooms to fruit varies slightly from species to species. But for most of the species that may be cultivated in New Zealand, a good rule of thumb is to aim for around 80 to 90% humidity. If you're not able to measure the humidity, that's OK, just keep in mind that you need a moist and humid environment to enable your mushrooms to fruit without drying out or cracking. On the other hand, too much humidity can cause mushrooms to become waterlogged and make them prone to contamination. So. You want 'lots' of humidity but not too much in your fruiting area. 

AIR EXCHANGE: This is a very critical aspect of fruiting mushrooms successfully. Air exchange is required to vent away the CO2 that mushrooms expel, and replenish the fresh air (oxygen) supplies to enable successful growth. Growing mushrooms in an enclosed space without adequate ventilation (like a tote bin thats too enclosed) will create spindly, leggy mushrooms with long, weak stems and small caps. Additionally, some air flow (or air movement) is beneficial in a fruiting space, to keep the air circulating and prevent moisture accumulation on the mushrooms. So. You want both a way for CO2 to escape and oxygen to be introduced, as well as a bit of air movement inside the fruiting area itself. 

TEMPERATURE: Most of the mushroom cultures that MycoLogic supplies are either native to New Zealand or are strains which are adapted to our climates. Our goal is to make mushroom growing easy and at the ambient temperatures found in New Zealand. As such, you shouldn't need to heat or cool your fruiting space too much, however mid winter in the deep south or mid summer in hot areas can on occasion be problematic for mushroom growing. 

LIGHT: Mushrooms do not need light to grow and survive, but they do need light to trigger the formation of fruit bodies. Some light is also beneficial for improved colour of mushrooms. Mushrooms grown in the dark or very low light conditions are usually pale in colour. Having said that, only the most basic of light is needed. A single 'energy saver' or LED light bulb, or a bit of natural light, for a few hours per day, is entirely adequate for mushroom growing. 

Some specific parameters about fruiting for various species are shown below:

 
 

SHIITAKE / NZ SHIITAKE 

Lentinula edodes and Lentinula novae-zelandiae

When to fruit: After around 3 months incubation, when the surface of the substrate has become 'popcorned' (bumpy all over the surface). For L. edodes the block will often turn brown all over and form a leathery skin, then its ready to fruit. For native NZ shiitake L. novae-zelandiae, the blocks do not brown so much, when the block is fully popcorned for at least a week or two it can be put into fruiting conditions. 

How to fruit: Remove the bag from the block entirely. Shiitake is fruited as a 'naked' block. It can be beneficial to flip the block upside down when you place it in the fruiting chamber. More fruits tend to form on the bottom of the block (when it was incubated) so flipping it makes these fruits come out on the top. 

Other notes: Primordia should begin to form about two weeks after putting into fruiting conditons. Some people trigger fruiting by hitting / slapping a fruiting block or spraying it with a high pressure water spray to cause mild damage to the surface of the mycelium. Fruit bodies mature approximately one week after primordia form. NZ Shiitake is harder to grow and produces lower yields than Asian Shiitake. Bran supplemented substrates are preferred for shiitake (15% bran 85% hardwood sawdust).
 

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OYSTER MUSHROOMS
Pleurotus pulmonarius and Pleurotus parsonsiae

When to fruit: After about 1-2 weeks incubation the substrate should have fully colonised with mycelium. Allow a few extra days for the mycelium to 'consolidate' / thicken up and then the block is ready to fruit. 

How to fruit: First, fold the top (empty) part of the bag down the side and tape it down to remove air gap from the top. Using a craft knife or sharp blade, cut an 'X' shape in the front of the fruiting block with each slit being 5-10cm long. This is where the fruit bodies will form. 

Other notes: Primordia should begin to form within one week of introducing to fruiting conditions. The mushrooms will naturally push out through the X cut. Fruit bodies will mature and be ready for harvest approximately one week after primordia form. Don't let them get over mature. Harvest when mushrooms are good size but caps are still dome shaped with inrolled edges. If edge of caps go flat or upturned they must be harvested immediately. Can be put back into fruiting conditions straight away for a 2nd, 3rd and possibly 4th flush. 
 

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PEKEPEKE-KIORE / NZ CORAL TOOTH

Hericium novae-zealandiae

When to fruit: The mycelium of this species can be fine and wispy and so you need to look closely to observe how well colonised the substrate is. Sometimes its more a change in the colour of the sawdust, than obvious mycelium that you're looking for. Blocks should generally colonise in about 2-3 weeks. Allow an extra week to make sure if needed. 

How to fruit: When the block is fully colonised, fold the top down and tape it (filter on the inside) to eliminate air gap at the top. Then, cut a small diamond shaped hole in the front face of the bag which is about 1-2cm wide and tall. The hole can be positioned slightly high on the bag taking into consideration the fruit will mostly 'dangle' down from there rather than grow much upwards. 

Other notes: Fruiting should commence within 1-2 weeks of putting into fruiting conditions. From there, fruit bodies can take a minimum of 1 week if not 2+ weeks to be ready for harvest. Pekepeke-kiore thankfully has a fairly wide window of 'harvesting opportunity'. If you notice the teeth becoming very elongated and the growth of the fruit slows down, its time to harvest, however can be harvested earlier as well for a denser fruit. Two to three croppings are easily possible from a block. 

TAWAKA

Cyclocybe parasitica

When to fruit: The block should become colonised with mycelium after two to three weeks. Allow an extra few days for consolidation of mycelium. When the block looks well colonised with white mycelium, its ready to fruit. 

How to fruit: Tawaka performs well when 'top fruited' from a sawdust block. To do this, cut the top of the bag off, leaving a good 5 to 10cm of extra bag space above the level of the substrate which creates a humidity pocket which helps the mushrooms to fruit. 'Side fruiting' around the edges of the bag can be an issue with tawaka. To prevent this, a rubber band can be placed around the fruiting block near the top of the substrate level, which encourages mushrooms to form at the top where fresh air is more abundant. If the mycelium has formed a thick leathery surface, it can be scratched with a clean knife to create fresh sites for primordia to form. 

Other notes: Primordia (initial fruit bodies) should begin to form after one to three weeks in fruiting conditions. From here, mushrooms will take about a week to be ready for harvest, depending on preference. Tawaka can be harvested any time from when the caps begin to widen and expand either before or after the veil is broken. As caps widen and flatten out significantly then harvest should be done with haste. Two to three flushes are common. 

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ENOKI 

Flammulina velutipes

When to fruit: Enoki mycelium should colonise a block within two weeks of inoculation. When the block is fully covered in dense, white mycelium, its ready to fruit. 
How to fruit: Enoki are a cold weather loving strain. Growing them in the summer is challenging. They're best suited to growing in autumn, winter and spring. They are best grown 'top fruited'. Cut the very top of the bag off, leaving a high 'collar' of empty bag at the top, and place a rubber band around the top of the sawdust block to prevent side fruiting around the edges of the substrate. Scoring the top surface of the block of mycelium with a clean blade is known to help stimulate enoki fruit body formation. 

Other notes: Fruit bodies should begin to form after one to two weeks in fruiting conditions. Enoki forms a dense cluster of many dozens or hundreds of fruit bodies. If a collar is left on the bag these will stretch into long skinny fruits which is desirable for the species. They can be harvested after one to two weeks of growth when the caps begin to flatten. Two or three flushes is achievable from a block. Enoki are also often grown in jars and fruited from the top by taking the lid off.

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TURKEY TAIL

Trametes versicolor

When to fruit: Turkey tail has a vigorous and thick mycelium. It will colonise a sawdust block rapidly within one to two weeks of inoculation. When the block is dense and white on the surface, it is ready to fruit. 

How to fruit: Turkey tail is fruited in various ways including top fruiting and slits in the bag. I prefer slits method for more even spread of fruit bodies. Fold the top of the bag down (filter patch on the inside) and tape it to eliminate air gap at the top of the bag. Then, cut three vertical slits in the front face of the bag - one hard left, one in the middle, and one hard right, to form three evenly spaced vertical fruiting zones on the bag. 
Other notes: Turkey tails is a slow growing mushroom. First signs of growth will occur within a week or two with some blobs of thickened mycelium beginning to emerge from the vertical slits. From here, these will continue to develop into strips of horizontal shelves that will continue to grow in size over the course of a couple of months. Harvest whenever you want although its best to wait until fruits are at least 5cm wide before harvest. You can expect two flushes of fruit from a turkey tail block. 

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