We have been introducing mushroom cultivation as a nutritional supplement and cash crop for the landless poor. Oyster mushrooms are a high yield, fast growing crop. They are known to help lower cholesterol levels and are a great source of potassium, iron and protein.
This instructable gives a low tech, step by step guide to growing both pleurotus ostreatus (winter strain) and pleurotus pulmonarius (summer strain). Oyster mushrooms are highly tolerant of variations in temperature, humidity, light levels and carbon dioxide levels, making it a great choice for first time growers.
See related instructable - How to Grow Oyster Mushroom Spawn (Low Tech)
Step 1: Materials
You will need...
Straw (the medium for growing the mushrooms in)
Containers (for soaking straw)
Plastic bags (or reusable containers for holding straw)
Elastic bands or string (to constrict bag opening)
Cotton wool (to filter out contaminants)
Barrel or drum (for pasteurising the straw)
Material liner (for holding bags within barrel)
Gas burner (for heating barrel)
Bleach spray (to clean growing room)
Spoon, gloves, clean clothes, face mask (to look the part when inoculating straw)
A growing area that can retain moisture in the air, shaded with some light
Possibly plastic sheeting (to help retain humidity & to reduce other unwanted moulds)
Mushroom spawn (see How to Grow Mushroom Spawn)
A water or weed sprayer (to increase humidity within growing room)
A thermometer and hygrometer (to keep an eye on temperature and relative humidity)
Step 2: Soak Straw, Drain and Bag
The mushrooms require a medium to grow in, in this case we will be using straw. The straw length should be approximately 5-10 cm (2-4 inches). Placing the straw in water tight containers, submerge the straw in water for 24 hours. Wash, rinse and drain thoroughly, then bag in 5 litre plastic bags ready for pasteurising.
Step 3: Pasteurise
Position your drum onto the heat source (we used a gas burner), pouring around 40 litres of water into the drum. Place a suitable platform at the bottom of the drum, one that will keep the bags above the water yet allow steam to rise. Insert a material bin liner and fill with the prepared bags of straw. Close off the bags with the liner and cover the drum with a lid. Heat the drum, steaming the bags for approximately 60 minutes. It should take around 30 minutes for the steam to make its way to the top bags (the temperature should near 95°C ~200°F). Leave to cool, removing the bags and transferring them to the growing area.
Step 4: Prepare Growing Room
The growing room should be clean and dimly lit (shaded with indirect sunlight), able to retain moisture in the air yet also provide an airflow when ventilation is needed. Plastic sheeting can be used to seal off an area to help retain humidity and to reduce other unwanted moulds and insects.
To prepare the room for the inoculations, spray a 1:20 (5%) solution of bleach along walls and corners (any area where mould might like to grow).
Temperatures of 10°C to 24°C (50°F to 75°F) for pleurotus ostreatus (winter) and 10°C to 30°C (50°F to 85°F) for pleurotus pulmonarius (summer) should be available depending on stage of growth (initial spawn run, colonisation, pinning and fruiting).
Step 5: Inoculate Bags
Before inoculating the bags of straw, make sure you have showered and are wearing clean clothes. Clean your hands with antibacterial soap or wear sterile gloves. A face mask and hair cap will also help reduce contamination (we are very dirty creatures).
Open the bags of straw and the mushroom spawn. Taking a sterile spoon, place a few spoonfuls into the straw, breaking it up and mixing lightly. As a general rule, the more spawn you add, the faster the substrate will be colonised (with 1 litre of spawn, we inoculated about 10 bags - you could inoculate more).
Restrict the opening of the bag by placing a rubber band (or cord) around the bag's neck. Taking a small piece of cotton wool, plug the bag's opening to reduce the chances of contamination and insect infestation. Leave to incubate.
Step 6: Encourage Colonisation
Once inoculated, the bags should be left to incubate. During this time the spawn "runs" (mycelium spreads) throughout the straw. The spawn run will be complete when the mycelium has spread entirely throughout the bag (the straw is then fully colonised).
Depending on the mushroom variety, humidity and temperature, this process should take between 1 to 3 weeks.
Pleurotus ostreatus (winter), 24°C (75°F) 2 to 3 weeks
Pleurotus pulmonarius (summer), 24°C to 30°C (75 to 85°F) 1 to 2 weeks
During incubation, light is not required, however, make sure the bags have plenty of fresh air.
Step 7: Monitor Bags
It is important to monitor the bags for any sign of unwanted moulds and pests. While the straw is still in the bags, you shouldn't have a problem with insects or mice. However, the best policy for fighting both contamination and infestation, is prevention. You may want to spray some surfaces to deter flies and other insects from setting up home, mesh any windows and keep doors closed.
Regularly check bags for any mould contamination and remove any infected bags from the growing area. Black mould found within the straw may indicate ineffective sterilisation. You may also notice sprouting straw and the appearance of unwanted mushrooms such as the ink cap (see pictures). Green moulds are common and can be caused by contaminated spawn (ineffective grain sterilisation), high moisture / low spawn levels and ineffective straw sterilisation. At this early stage, it is better to simply remove infected bags, as you want to prevent its spread. Up to a 10% loss due to contamination is generally regarded as acceptable.
Finally, as the bags become fully colonised, the initial stages of fruiting (or pinning) may be seen.
Step 8: Encourage Pinning
Once pinning has started, it is time to remove the substrate from the bags. Pinning naturally occurs as humidity increases, low levels of light appear and temperature levels fall. Increase the growing room humidity by regularly spraying with a water sprayer (avoid spraying directly on the mushrooms). You can also wet the floor and leave open containers of water in the room (95-100% humidity is recommended). As our climate is very dry, we only managed 60% at best, dropping down to 40%, by spraying 5 litres of water 2 - 3 times a day (even at these humidity levels a good result can be achieved). To prevent excessive CO2 levels, allow the growing area to flush with clean air before spraying. If you can, regulate the temperature accordingly.
Pleurotus ostreatus (winter), 10-15°C (50-60°F)
Pleurotus pulmonarius (summer), 10-24°C to 30°C (50-75°F)
You may notice an initial drying out of early stage pinning, as you remove the plastic. As you maintain the humidity levels this will regenerate. Keep a close eye on flies and spray when needed. If any mould is found, either remove the infected straw or the entire mound from the growing area.
Step 9: Harvesting
As the mushrooms begin fruiting, it is important to keep the humidity high (85-90% is recommended). As before, allow air to flush through the growing area prior to spraying (oyster mushrooms require a consistent source of fresh air). Temperatures can now be higher than for the initial pinning stage.
Pleurotus ostreatus (winter), 10°C to 20°C (~50°F to 70°F)
Pleurotus pulmonarius (summer), 16°C to 28°C (~60°F to 80°F)
Remember to constantly monitor for pests, such as flies and mice, as they can quickly ruin a crop. You should expect three or more crops, each taking around a week or so to mature. You may harvest the mushrooms at any size, however, once a mushroom has reached its full size, you will notice it will begin to dry, turning a yellowish colour (they taste great, even dry). When harvesting, remove the mushroom completely, by twisting firmly at its base. After harvesting a few crops, we found it helpful to stack the mounds of straw, which seemed to help increase the yield. If you find your mushrooms with long stalks and small caps, they may not be getting enough light, also high CO2 levels can also lead to small deformities (allow for more fresh air). After the straw ceases to produce mushrooms, it can be fed to livestock or composted.
Now, finally take your harvested mushrooms and create a delicious mushroom meal. Enjoy.
See related instructable - How to Grow Oyster Mushroom Spawn (Low Tech)