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Grey Oyster Mushroom spawn is an easily cultivated mushroom appropriate for beginners, because of its vigorous mycelium growth. The mushroom can efficiently compete with other fungi while growing on a substrate and is thus resistant to molds.
Grain spawn will store for three months in a refrigerator while sawdust spawn will store for six months to a year. The fresher the better, but mycelium is pretty resilient. If you don’t get around to inoculating right away, tuck it away in your refrigerator until you’re ready.
Unlike intensive indoor cultivation or growing kits on logs, making mushroom beds is easy and doesn’t require any special tools or technology.
Where pest pressure is high, sawdust spawn is a better choice than grain spawn. Grain spawn can however give a boost of nitrogen to carbon-heavy substrates such as hardwood leaves, straw, and sawdust. One bag of spawns can inoculate a 4’x4’ space or roughly 16 square feet.
Different species have different substrate preferences! Refer to the section on the species you will be growing for information on what substrate is best to use in your bed. If you create a bed with a substrate composed of smaller particle sizes or create a casing layer for your bed testing the field capacity of your substrate is a helpful practice!
Keep your mushroom bed watered as you would plant in a garden. The substrate should be moist but not soggy.
Brown Cardboard (Optional)
If there’s grass or stubborn weeds growing on your site, you can help to smother them by laying down some brown cardboard first. Keeping the cardboard in place is optional but can help in weed suppression. Saturate the cardboard before beginning to layer on your substrate.
Pleurotus ostreatus., are the most vigorous mushrooms that we cultivate, readily outgrowing competitors and potential contaminants. These brightly colored mushrooms are pretty adaptable both in temperature and substrate preference. Meaty in texture and flavor, they’re truly a culinary delight. For these reasons, oyster mushrooms are well suited for beginners looking to get their feet wet in outdoor mushroom growing. Grain spawn or sawdust spawn will work well here since oyster mushrooms grow so quickly. All the oyster varieties can be grown in outdoor beds including yellow, pink, summer, lion’s mane, beech, pearl, princess, grey, milky, chestnut, hybrid grey, white, king and trumpet. White oyster mushrooms are a heat-loving species and should only be planted when average temperatures reach 20-25 degrees C. Take note that this species will die under 35 degrees F and therefore may not overwinter depending on your grow zone.
Straw, agricultural byproducts, hardwood chips.
Oysters prefer straw to denser woody substrates such as wood chips. You can soak your straw beforehand if you want, spray it between the layers, or water it all in one go at the end. Feel free to use other agricultural byproducts here in place of straw - sometimes the best material is the one easiest to find!
Step 1: Get Prepared
Decide which oyster mushroom substrate to grow on
Substrates are the food source that enables the growth of mycelium.
Mycelium is the root-like vegetative growth of the fungus and is critical to the cultivation of oyster mushrooms in the same way an apple tree is to an apple.
The most widely used substrate for oyster mushrooms is straw. However, sawdust, cardboard, coffee grounds, and other byproducts of agriculture such as cotton waste can also be used.
Straw is a very forgiving substrate to grow on.
Choose a substrate material that you can easily source and use the instructions below to prepare it for inoculation.
If you want to skip the learning curve of making your own substrate, you could also consider buying ready-to-fruit oyster mushroom blocks which come fully colonized and ready to grow.
Order Your Supplies
Before you get started on the growing, the last step is getting your supplies ready so you can get started.
You’ll need to order:
Grain spawn will produce bigger yields than sawdust spawn, so try to source this if you can.
As for growing containers, ideally, you’ll get hold of purpose-made mushroom cultivation bags. They enable the perfect air exchange and keep out competing molds and bacteria.
The goal of the substrate is to provide a hydrated nutrient-dense food source that is also devoid of other micro-organisms that would normally compete with the mushroom mycelium.
Straw, cardboard, sawdust pellets, and coffee grounds are all easy substrates to use for growing oyster mushrooms that achieve this goal.
Here’s a quick overview of how to prepare each one.
Straw is the most commonly used substrate for oyster mushroom cultivation. It is usually cheap and contains essential nutrients and oyster mushrooms thrive on it.
Pasteurize by soaking in hot water (65-80C / 149-176 F) for 1-2 hours, or in a cold water high-pH lime bath for 12-18 hours.
The great thing about using these is that they are already pasteurized by the heat and pressure of the pellet production process.
Add equal weight of water to the weight of pellets, soak for 30 mins. And then mix to break up the pellets into hydrated sawdust.
Waste coffee grounds are a plentiful (and already pasteurized) resource.
Despite a lot of misinformation on the internet, coffee grounds can actually be a pretty good substrate for growing oyster mushrooms.
The key is to only use fresh grounds (within 24 hours of brewing) which are already pasteurized and hydrated by the coffee brewing process.
Beyond 24 hours, competing molds start to develop and will outcompete your mycelium.
Ideal as a substrate on its own in small amounts (1kg or less), but if you go bigger, mix in 20-50% of the straw.
Inoculation is the process of adding your mushroom spawn to your prepared substrate.
Before you start mixing, clean your hands well with soap and wipe down all surfaces you’re about to work on with a cleaning spray.
Make sure your substrate has the right moisture content. The pasteurization process will probably moisten your substrate to the correct level, but it’s essential to check that your substrate is not too dry or too wet.
Depending on the material, you are aiming for anything between 55% hydration (sawdust and coffee grounds) to 74% (straw). The easiest way to check is with the squeeze test.
Squeeze the substrate slightly in your hand. It should bind into a ball in your hand, and a couple of drops of water should come out. If more than this occurs, you’ll need to dry your substrate out a bit. If it doesn’t hold together in your hand, it is likely too dry, and you’ll need to add more water.
Next, mix the substrate and mushroom spawn in a container of some sort (large plastic box, barrel, whatever you have to hand) then load the substrate into your growing vessels and close the top with a rubber band, paperclip, tape, or tie of some kind.
If you’re not using a filter patch bag, then make a few tiny holes every 10cms around the bag for air exchange.
Incubation is where the magic begins!
It’s where the spawn that you introduced will grow and spread out across the substrate, in preparation for the final phase of fruiting.
Providing the condition needed for incubation is simple, even at home.
You can use any warm (20-24C) space in your house, like a cupboard or boiler room. The area should ideally be dark to prevent early pinning, but it’s not essential.
The spawn will come to life in the warm, humid conditions of the bags and eat its way across the food you’ve given it.
Once the bag is completely white, it’s time to start fruiting.
If it’s just a little, there’s a good chance that your spawn will overtake it, but if there’s a lot, the growth will likely fail, and it’s time to compost your substrate and start again.
Now for the moment, you’ve really been waiting for!
After all your efforts, it’s time to reap the reward and harvest some delicious oyster mushrooms.
Mushrooms grow in the wild in response to stress (like running out of food) or to changes in their environment.
You want to replicate this process in your home or garden.
Once the bag is fully colonized (i.e. the mycelium is soon going to run out of food) it will now be keen to grow mushrooms in a bid for survival.
All you need to do is provide the optimal conditions for the mushrooms to develop:
While direct sunlight is not a good idea, some indirect or shaded light is needed for the fruitbodies to form properly. They don’t gain energy from the light, so an indirect lighting source or shaded windowsill will be sufficient.
In the wild oyster mushrooms are used to growing out of a stump or log in fresh oxygen-rich air. Providing a 5cm slit or hole in your bag will signal to the mycelium that there is a space to grow out from.
Spray with water twice a day to keep the substrate hydrated and the environment in which the mushrooms are developing humid. This will encourage the mushrooms to form and stop them from drying out as they develop.
This is specific to each strain, but generally (with the exception of king oysters) most oyster mushroom strains are not too fussy about what temperature they will grow at. They will form best in their ideal range as mentioned in the strains info above, but as long as it is in the range of 20-25C (50-86F) they should still fruit.
Within 7 days you should start seeing tiny mushroom pins forming out of the hole.
Once the edge of the caps of the oyster mushroom starts to flatten out or turn upwards, it’s time to harvest before they begin dropping lots of spores.
This can be difficult to judge the first time around, but you soon get a feel for it.
A couple of tips: if you see them stop growing any bigger, start to dry out, or drop lots of white “dust” (spores) then it is time to harvest!
Harvesting just as the edge of the mushroom caps begin to flatten out.
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