Instructions for the Elm Oyster Mushroom Kit Print E-mail
Thursday, 24 September 2009 14:24


Your Elm Oyster kit contains live mycelium of the species Hypsizygus ulmarius, called Shirotamogitake by the Japanese. These mushrooms grow on various dead or dying hardwood trees. You will prepare an artificial growing environment that simulates the conditions in a dead or dying tree trunk or branch by combining hardwood sawdust, water, and coffee grounds. 


Contents of the kit: 

  • poly bag of live Hypsizygus ulmarius grain spawn
  • bag of hardwood sawdust pellets (including supplemental limestone and gypsum)
  • poly filter bag

 Additional materials you will need:

  • about two cups of freshly-used coffee grounds, drained of excess moisture
  • a clean mixing bucket or bowl of a least 1.5 gallon capacity
  • a thermal food storage sealer, or strong adhesive tape
  • isopropyl alcohol solution
  • three cups of hot tap water*

 Preparing the Substrate

  1. Collect your coffee grounds. Drain them of any free-running liquid, so they remain moist but not sodden. If you need to collect them over time to get enough, keep them in the refrigerator or freezer in a closed container until you have the 2 cups you need - but thaw them to room temperature before using them! 
  2. Choose a workspace where you can minimize the amount of air movement. Turn off fans, close windows, and keep others from entering while you work. Prepare your materials and your workspace so you can work quickly to minimize the exposure of the ingredients to airborne contaminants. You don't need a sterile environment, just a reasonably clean and quiet one.
  3. Before mixing the substrate, wash your hands thoroughly with soap and water and wipe them with alcohol solution to reduce the chance of contaminating the mix. It's a good, but not strictly essential, practice to give all the surfaces that will come into contact with the mix, like the mixing container and table top,  a wipe-down with an alcohol-moistened paper towel. 
  4. Empty the bag of sawdust pellets into your mixing container. Take the hot water from your sink and add it to the sawdust pellets and mix them up by hand or with a clean mixing spoon until they break apart.
  5. Add the coffee grounds to the bucket and mix well. I f the mixture still feels warm, let it cool to room temperature before continuing. 


  1. Squeeze the bag of grain spawn to break apart the grains. Cut open the bag, pour in the spawn, and mix it in quickly but thoroughly. Break up any remaining clumps in the mix.
  2. Pour the mixture into the filter bag then seal it tightly. Use a food storage thermal sealer if you have one, otherwise fold the top inch of the bag over and tape it securely. Don't tape over the filter patch! There should be some space in the top of the bag for air to circulate.



Place your bag of mycelium in a safe place where it can incubate at room temperature. 70°F is ideal, but your H. ulmarius can thrive during this phase at any temperature between 60°F and 80°F. It requires no light or watering during this period. 

Within days you will see the mycelium grow from the individual pieces of grain and eventually throughout the bag, forming a thick, essentially solid white mass.

Mycelial threads radiate from grain spawn kernels


After 3 to 6 weeks, it will mature and produce pools of yellow liquid. These indicate that your mushrooms are ready to begin fruiting!


Make an X-shaped incision about 1-2 inches across on one end of your filter bag where you find fairly dense mycelial growth. The best-looking mushrooms grow out the side of the bag, rather than on top, and limiting exposure to the open air can improve your chances of getting multiple fruitings, or flushes. It can help to fold the top over the side of the bag to limit air flow through the filter patch at this time, and to shade the top of the substrate, but not the end of the bag where you want the mushrooms to form.

Ideally, to stimulate formation of primordia, or pinheads, you would like to drop the temperature to close to 50°F, but you also need to provide light and a humid atmosphere around the kit, and you may find it difficult to provide all these conditions simultaneously. Fortunately, your mycelium will still fruit at higher temperatures, though perhaps not so predictably, so if you do not have a conveniently cool, well-lit place for your kit, concentrate on providing light and high humidity.

You will want to keep the relative humidity at or above 80% as much as possible. Mist the opening, and eventually the emerging mushrooms, 2 to 4 times daily with water from a spray bottle.

If you have very dry air - a common problem during the winter - consider making a humidity tent out of clear plastic to cover it with between mistings. If you use a tent, make sure not to seal off the kit entirely; it needs to exhaust carbon dioxide and take in fresh air. 

During the pinhead formation and fruiting phase, the mushrooms should have indirect sunlight, or bright artificial light, but never direct sun. You should see pinheads form in 1-3 weeks. 

If your outside weather conditions match the requirements described here, you may put the bag outside to fruit in the shade. Check it frequently, though, as slugs and other pests love these mushrooms. 

Small primordial mass

 Large primordial mass


If pinheads form on top of the mycelial mass, inside the bag rather than out of the hole on the end, you can open the top to let them grow out of the bag, but do so gradually to let them adjust to the changing conditions. Start with a small incision near the surface of the substrate and extend it daily until the pinheads have enough room to grow out of the opening. Remember, if you cut off other sources of air, like the filter patch, the mushrooms should find their way out through the opening.

The mycelium may produce multiple clusters of primordia which will compete with each other for nutrients from the material they are growing in. One of the clusters will typically overtake the others and will grow large.

You can tell when a mushroom is ready to be harvested by the way the cap looks. When a mushroom is about to sporulate, the edge of the cap turns up, exposing more of the gills. You will want to harvest your mushrooms before this happens. You want your mushrooms to be as big as they can get, but you don't want them to spoil, so you should harvest them when the edges of the cap are still turned down a little. 

Mature caps from above 


Mature caps, frontal view 

Harvest them by twisting the whole cluster gently by the base of the stems until it comes loose. Trim off any sawdusty substrate. Now you can cook up something tasty with your own homegrown mushrooms!

After you have harvested your first batch, stop misting the bag of mycelium and in a week or two you may see more primordia beginning to form. If they appear, begin misting the block again and you will have a second batch, and eventually even a third, batch.


Eventually your substrate will get contaminated by other organisms - mold, bacteria, even algae. You just cannot keep them all out. Unless contamination gets way out of hand, your mushroom will probably still flourish.

Contamination will appear as areas of green, blue-green, yellow, orange, red, brown, or black that increase in size and overrun the white mycelium. Ideally, your kit will turn from sawdust-and-coffee brown to white, with a pale yellow fluid appearing when it's mature. Anything else probably results from contamination. As long as it doesn't seem to overwhelm the mycelium, everything will probably turn out fine. 

 It helps to think of growing mushrooms as a contest between the many organisms that can grow in the substrate you have provided. Your kit contains a relatively large amount of grain spawn for the volume of substrate you prepare, which greatly increases the odds that your fungus will overwhelm any competitors that might gain a foothold. But there's no guarantee. Too much water, too little air, ingredients left out on the counter collecting contaminant spores - lots of things can diminish the advantages your mushroom culture enjoys. For that reason we recommend that you follow these instructions as closely as possible. Don't start to improvise until you have gone through the process successfully once or twice!


*if you have heavily chlorinated tap water, let it sit for a day to lose its chlorine, or use bottled spring or well, but not distilled, water 


Last Updated on Monday, 24 January 2011 10:51