How to grow mushrooms at home: the winning Multi-Armed Bandit experiment recipe

This article describes the bandit (recipe to grow oyster mushrooms) with the highest average reward following one year of growing mushrooms as described in my Multi-Armed Bandit experiment. The good news? It is the simplest recipe. The bad news? It is a recipe that works well in cold climates. I grow them in my basement at temperatures ranging from 15c (60F) to 23c (73F).

To do this recipe, you will need:

  1. 3 quarts of blue/gray oyster (Pleurotus ostreatus variety columbinus) mycelium (that you purchase or grow yourself). To learn how to grow mycelium on grain, read for instance this article, which is the method I use (note that this recipe was not part of the Multi-Armed Bandit experiment, I used the same approach for all bandits).

    A jar of homegrown mycelium in white millet.
  2. three multi-purpose 5 gallons buckets (that you can find at a hardware store. I got mines for free from a friend who got them from a restaurant, which ensures they are made of food grade high density poly ethylene). Drill 1″ holes on the sides of one bucket, randomly, maybe a total about 15 holes. Also drill a few smaller holes, maybe 1/8″, at the bottom to allow drainage. Don’t drill any hole in the other two buckets. The idea is that in the first part of the process, you will put the drilled bucket inside one of the other buckets. When the mushroom are ready to fruit, you will separate the buckets and the mushroom will grow through the holes.

    A bucket drilled with 1″ holes. Buckets need to be clean. I first use water and soap, then a bit of bleach.
  3. hardwood pellets, that is, pellets for pellet stoves. A 40 pounds bag should cost about $5. Make sure that the pellets are made of hardwood (oyster mushrooms don’t like softwood) and that no chemical is added (usually, the pellets are not glued and contain no additive, they are processed under high pressure, which caused heating and release natural lignins that binds the sawdust into pellets).
  4. a mini greenhouse, like this one. Ideally you will also have a small table fan and a humidifier (preferably a cold mist one). I created two small openings at the top of the greenhouse (about 4″ long). At the bottom, on one side, the fan pushes fresh air inside the greenhouse, while the humidifier, on the other side, provides humidity. The goal is to maintain humidity level between 80-95% while providing fresh air. When growing, oyster mushrooms produce CO2 like crazy. If no fresh air enters the greenhouse, the mushrooms will be malformed.

Instructions (do this ideally in a clean room. The worst room is the kitchen: plenty of bacteria and contaminants. You can spray Lysol 10 minutes before in the room):

  1. Boil some water.
  2. In one hole-free bucket, add a layer of pellets, an inch or so
  3. Slowly add boiling water until all the pellets turn to wet sawdust, but no more than required. Mix with a big spoon.
  4. Repeat until you reach maybe 4 inches from the top of the bucket
  5. Let it cool down for 12 hours or until the temperature is lower than 86F. You can mix one or two times, to help the cooling process. If the substrate temperature is higher than 100F, you risk killing part of the mycelium.
  6.  Put the bucket with holes inside the unused third bucket
  7. Add a layer of sawdust, a few inches at a time
  8. Transfer some mycelium. Maybe 1/8 of a jar at a time. Mix with a spoon.
  9. Repeat 7-8 until you reach the top of the bucket
  10. Put the lid. Wait 7-10 days.
  11. Open the lid: the top should be completely white. Separate the buckets: the holes should also be white. That means mycelium has colonized the substrate. If some of the holes are not white, colonization is not over. If the colonization is not complete, put the bucket back inside the other bucket and wait a few days, until all holes are white.
    When fully colonized, the top is almost completely white. Water droplets at the top is okay as long as they are not amber. Amber droplets usually means the mycelium is fighting contaminants and releasing metabolites to protect itself.
    This hole is not showing a significant presence of mycelium. This bucket is not ready.

    This one looks better. It is normal to still see some brown
  12. Put the bucket with holes inside the greenhouse with the lid on. The greenhouse should be located in a cold location (under 24C or 75F, ideally colder than that) and kept at about 90% humidity.
  13. Wait until primordia/pins appear.

    Primordia or pinning. It looks like a cauliflower, and it is a sign that mushroom have started growing. From now on, everything will go quick and mushrooms will be ready to harvest in 5-7 days. Fresh air is now required!
  14. Start the fan and humidifier. A bit of fine-tuning may be required here. The goal is to provide sufficient fresh air (to get rid of the C02 that would otherwise be building up inside the greenhouse), while maintaining humidity levels above 85%. I use a programmable timer to reach that goal.
  15. 5-7 days later, the mushrooms should be ready to harvest. Initially, the caps of oyster mushrooms are convex. As they grow, the caps flatten and then turn concave. The best is to harvest the cluster when the biggest mushroom is turning concave.
    The two rightmost clusters are ready to harvest

    Now you are ready to cook’em and eat’em!