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Beginner’s Guide to Growing Oyster Mushrooms

Oyster Mushroom

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Basic Requirements

1. Growing House

A well-prepared mushroom house providing for darkness and dampness with:

  • Solid floor (no mud)
  • Solid roof (no rain or light)
  • Adjustable air vents (not used for first two weeks)
  • Racks to carry the bags

The racks can made of treated or untreated timber and must be strong enough to carry the weight of many bags (described below).  It is quite feasible to pack 200 bags in a room that is approximately 20’ by 13’ by 9’ (6m by 4m by 3m).

The space between the rows must accommodate the free movement of a person tending to the mushrooms while the space between the bags must allow the mushrooms to sprout out of the bags without touching each other. This compact system utilizes the space efficiently and maximizes productivity.

mushroom growing house

The shed pictured above is insulated with sheets of hard foam insulation.


Warning – learn from my mistake!

In preparation for writing this article I created a much smaller (3’ by 3’ by 3’) “mushroom growing box” around the legs of a table, insulated with cardboard and old carpet and covered inside and out with heavy-duty black plastic.  This did not work well – the spawn populated the bags and tried to grow but remained as undeveloped spikes which never managed to form mushrooms until the bags were moved into a bigger space with better ventilation and light. The completely sealed box was just too hot and airless for the mushrooms to mature. )


2. Any Crop Residue As Substrate

The “substrate” is the surface or material on which the oyster mushroom fungus lives, grows, or obtains its nourishment. Many, different well-dried crop residues can be used for oyster mushroom growing, for example: maize or corn stover (stalks, leaves, husks, and cobs), wheat straw, banana leaves, ground nut stalks, bean stalks or general hay provide a healthy substrate for oyster mushroom production. I used cotton waste – specifically cottonseed hulls which are the fibrous outer coverings of cotton seeds and the by-products of the dehulling necessary for cottonseed oil extraction. This looks like coarse dirty cotton, full of the spikey covers of cotton seeds and is a perfect medium for growing oyster mushrooms. (It is ridiculously cheap and very light – I started off with a couple of garbage bags full, which cost me $2.00.)

cottenseed hulls for substrate
Cottonseed hulls for substrate

3. Very Large Pots or Drums

For soaking or boiling the substrate.

4. Planting Bags

Clear plastic bags, reasonably robust and between 22 and 44 lb (10 and 20 kg) in size

5. Spawn (Mushroom “Seed”)

Mushroom spawn is any substance that has been “inoculated” with mycelium, the vegetative growth of a fungus. Mycelium, a thread-like collection of cells, is to a mushroom like an apple tree is to an apple. The spawn is used to transfer mycelium onto the substrate. You need to buy it from a reputable supplier in your area when you are ready to set off – you can keep it in the fridge for up to five days but it is best to use it as soon as possible.

mushroom spawn
Spawn, as delivered by the supplier

6. Water

Regular clean supply

7. Equipment for Mist Spraying

For example – a hand-held spray bottle

8. Bailing Wire or Twine/String

For hanging up the bags

9. Thermometer

Ideally – to monitor the growing environment

10. Chemicals for Disinfecting

Any bleach will work for disinfecting.

Steps To Growing

1. Disinfecting Your Growing Space

The process of growing edible mushrooms can be disrupted by invasions of other opportunistic fungi taking advantage of the ideal fungus growing conditions. It is essential that all your mushroom growing equipment and spaces are clean and thoroughly disinfected. Before you begin, spray all the surfaces of your mushroom house with a water and bleach solution – the walls and floors and the racks. The mixture for this process can be one part commercial bleach or disinfectant to nine parts water.

2. Preparation of Raw Materials Substrate

  • Chopping: The dry crop residue or raw material should be chopped to make it short and soft to increase its water absorption capacity and the substrate density.
  • Sterilizing: Big drums of water can be lined-up for the purpose of sterilizing the materials. There are two basic methods:
    • Boiling the substrate is by far the best and most efficient method although it can be more costly in terms of firewood or electricity bills.
    • Soaking in water treated with added commercial bleach.

The general principle is that the longer the sterilization period the better results in most cases. More specifically the length of time depends on how hard or soft the chosen materials are. Some crop residues are harder than others e.g. corn/maize stover is much harder than wheat straw therefore the sterilization of wheat straw should probably take a quarter of the time taken for maize stover.

Below are the recommended times:

Soaking in treated water:

  • maize stover, cobs, cotton hulls, etc. 1 to 2 days soaking time
  • wheat straw, hay, rice straw etc. 10 to 12 hours soaking time


– maize stover, cobs, cotton hulls etc. 2 to 3 hours boiling time
– wheat straw, hay, rice straw etc. 1 to 2 hours boiling time

boiling substrate

The disinfected substrate then needs to be spread out on racks to dry. (Disinfect the rack before spreading the substrate.)

drying substrate
Substrate drying on a rack



dried substrate
Dried substrate

You do not want the substrate to be bone dry. It is ready when a tiny bit of moisture runs out between the fingers when a handful is squeezed.

If you want to do a small trial, you can purchase substrate online.

>>check prices on Amazon>>

3. Packing of Bags For Spawning and Spawn Running

bag packed with substrate and spawn
Bag packed with substrate and spawn

The ready substrate is packed into plastic bags of between 22lb and 44lb (10kg and 20kg) sizes. (The implication of the size of the bags is that bags that are very big/heavy will produce more mushrooms BUT they will need very strong shelves to support them.)

The spawn is inserted in layers at every third level of the bag until the bag is full.

  • A 22 lb bag (10kg) should take 3 -4 oz (80-100g) of spawn which means one third of the bag takes a maximum of 1 oz (30g) of spawn.
  • A 44 lb bag (20kg) takes 3.5-4.2 oz (100g -120g) of spawn.

packing bag

  • The bags can be loosely packed – they naturally compress down during spawning.
  • Use a small nail to punch little holes in the sides of planted bags for air circulation.
  • Two bigger holes are inserted at the bottom of each bag to let out excess moisture from the spawned substrate.
  • Strong string or soft wire is used to tie-up the bags.
  • The prepared bags are hung in the mushroom house.


First Two Weeks (actually 3 weeks in winter and 8 days in hot summer)

For a period of two to three weeks the bags are left hanging in the room for a process called spawn-running or colonization. This means that the mycelium (the fungi which produces mushrooms) will cover the contents of the bags during that period.

This phase needs temperatures of 25-27° C/ 77-80° F for first 28 days. Note: Spawn is deactivated at very low and very high (30° C / 86°F and above) temperatures.

A successfully colonized bag looks solid and white – the substrate has been smothered in mycelium which has a slightly chalky look to it.

mushroom bag

When full colonization has taken place, the bags need to be perforated. Cut top-to-bottom vertical slits in each bag five or six times around the bag with a sharp object like a razor blade or a sharp knife. Some oyster mushroom growers remove the plastic completely leaving the colonized substrate stark naked. This is not recommended because it exposes the substrate and causing dryness that can terminate the yield too early. Whatever cutting method one adopts the mushrooms will still grow, covering the whole substrate.

Second Two Weeks

Two weeks after perforation pinheads develop and fully grown mushrooms will appear thereafter. It takes four to seven days from pinhead formation to development into fully grown mushrooms.

From now on there needs to be strict humidity control with the bags being in an atmosphere of 75-80% humidity. Mist spray in the mushroom house in the morning. Check around mid-day and if the surfaces of the bags seem to be dry spray again. (Do not encourage competitive fungi by over-watering. You do not want puddles lying about. )

mushroom bag 2

One Week Later

first harvest
First harvest


Two Months – Managing the Mushroom Crop

mushroom crop
Oyster mushrooms take five to six weeks from planting to harvesting.

Managing the mushroom crop requires a disciplined systematic regime. All cultivated mushrooms appear in flushes. A flush is a period of harvesting which can range from one day to four days of harvesting. There is usually a one week break between the flushes. All things being equal, 60% to 70% of the total yield is harvested between the first and third flushes.

After the first 28 days the mushrooms need a temperature between 15° and 20°. Too high or too low temperatures during fruiting periods can adversely affect crop yields. If necessary, you can bring high temperatures down with ice cubes on the floor.

A mushroom house must be kept damp from the day of planting until the end of the harvesting period. Because of its fragile, spread-out fan shape the oyster mushroom gets dry very quickly at any stage. Maintain the regime of mist spraying in the mushroom house in the morning and checking around mid-day to see if the surfaces of the bags seem to be dry. If dry, spray again. The whole bags can be soaked in water for half an hour if the contents appear to be altogether too dry.

Oyster mushrooms require a certain amount of light as well as lots of moisture. Experiment with exactly how much. (The bags hanging near the door in my mushroom house produced more lavishly than those hanging further from the periodic bursts of light caused by me opening the door to water the crop.)

Oysters can continue flushing for 4 to 6 months under good conditions and each bag will have produced up to 20 lbs (10 kg) of mushrooms depending on the size of the bag. If nothing more is showing up dip the bag in water to see if some more mushrooms can be coaxed out of it.



Picking and Packaging Your Mushroom Crop

The oysters can be loosely packed in plastic or brown paper bags or in punnets. Unnecessary storage of mushroom is not recommended. They should be eaten (or sold) as soon as possible.

However, they can be preserved very easily and satisfactorily by freezing or by dehydrating.

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