University of Vermont Extension 
Department of Plant and Soil Science

Late Winter/Spring News Article
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GROWING SHIITAKE MUSHROOMS

Dr. Leonard Perry, Extension Professor
University of Vermont
 
 
You may have seen shiitake mushrooms in stores or on restaurant menus, as they are becoming increasingly popular, and not just in gourmet cuisine.  One reason is for their flavor, meaty and buttery fresh, and smoky when dried.  They’re low in calories but high in protein, B vitamins, vitamin D, minerals, and dietary fiber.  They provide healthful flavonoid compounds, comparable to apple peels (the healthiest part of apples). With a few logs in a shady spot, and buying some of the “starter plugs”, you can grow shiitake mushrooms easily at home.
           
Shiitake mushrooms have been grown for thousands of years in Asia, originally found growing in the wild in mountainous regions.  Today, it is the second most grown mushroom in the world, next to the common button mushroom.  They are good in soups, stews, Asian and pasta dishes, with seafood or poultry.  The stems—tough to eat—are good in broths. 
           
The shiitake has a lightly convex “cap” or top, 3 to 6 inches across when mature.  It is light to dark brown, with white “gills” underneath.  The caps are on top of a 2 to 4-inch, light brown stem.  If you see such mushrooms naturally in the woods, make sure they are shiitake and not another similar species that may be toxic.  If you aren’t positive, check with a local mushroom expert or “mycologist”, often at a college or university.
           
Unlike many mushrooms which grow on compost or manure-based potting media, shiitake mushrooms grow on logs.  You’ll need to obtain or cut logs (“bolts”) about 3 to 6-inches across, and 3 to 4 feet long.  For ease of handling, consider the 3-foot lengths for the thicker logs.  The best logs are from hardwood trees (“shii” is “from hardwood trees” in Japanese), particularly oak and sugar maple.   Avoid fruit wood such as apples, ash, soft hardwoods such as aspen, or evergreens such as pine or spruce. 
           
Since this mushroom (as all mushrooms, this one is a fungus) doesn’t compete well with other wild fungi, logs should be freshly cut within one day to three weeks of use—the sooner the better.  Late winter and early spring is the best time to cut logs, but if you’re too busy then, you can cut them in winter and store until spring.  If storing, keep them off the ground so they get less contamination from rot and organisms, and keep them in shade or under a cover.
           
Once you have the logs, they need to be “inoculated” with the fungus.  Most find it easiest to order “plugs” of the inoculum.  You can easily find sources online by searching for “shiitake mushroom supplies”.  Since you’ll want to inoculate soon after cutting logs, you’ll want to order these plugs ahead of time.  You can store them in the refrigerator if needed.             

These plugs are just that, which you insert into holes drilled into the logs.  The plugs consist of sawdust, the fungal inoculum (usually called spores, but correctly they are fungal strands called “hyphae”), and some grain material for nutrients for the fungus.  Figure on a minimum 30 to 40 plugs per log, so a packet of 100 would be good for a couple logs. 
           
Drill holes the size of the plug in the log, making holes about 3 inches apart, and in staggered rows.  You may figure on one row for each inch log diameter, so a 5-inch wide log might have 5 rows of plugs. Then insert the plugs in the holes, and seal the holes so competing fungi won’t enter. 
           
Seal the holes with cheese wax (available from cheese companies or online suppliers), or bees wax (which can crack at very low temperatures), or paraffin.  While sealing the holes, also seal any areas missing or with damaged bark.  These areas can allow other fungi to enter.
           
As when storing logs, keep these inoculated ones off the ground, and in 80 percent to full shade.  The north side of a building can provide this, as can a burlap cover.  Don’t use an impermeable cover such as plastic, which keeps out air and rain. 
           
Direct sun and wind can damage the early fungal growth or “spawn”, and can dry out the logs. The fungus needs moisture from the wood to grow.  Ideally, moisture content of the wood should be above 35 percent. During drought spells you should wet the logs down well, as with a garden hose or under a sprinkler for a couple of hours.
           
So once you have the logs, and they are inoculated and sealed, they need a period (“spawn run”) of 8 to 18 months for the fungus to “colonize” or grow through the log.  This is usually done laying four logs horizontally, then another four on top in the other direction, and so on—a “crib stack”. 
           
The shiitake fungus should eventually “fruit” or produce mushrooms on its own, but this is unique in that more production can be forced sooner and around the same time by “shocking”.  This is simply done by soaking the logs in cold water for 12 to 24 hours, during the warmer months when night temperatures are generally above 50 degrees.  A pond or stream of cold water is ideal, but any large container will work such as a cattle trough, even a small children’s pool.
           
Once logs are shocked or forced, stack them in an A-frame arrangement, or simply leaning up at an angle against a structure or side of a building.  If they don’t fruit in a few weeks, you may need to shock again. Or, if they have fruited, allow them to rest for 6 to 8 weeks before shocking again.
           
A few days to week from shocking the logs, you should see small white dots or bumps the size of a pencil eraser.  These are called “pins” and this process of early mushroom growth is called “pinning”.  From this point until harvest, cover the logs with a white woven frost blanket (available from complete garden stores, or online), or even a sheet if cold or frost is predicted.  Cover logs and the growing mushrooms with a canopy or plastic cloth when rain is forecast.  Rain will cause soggy, waterlogged mushrooms. 
            
Covering logs with a white, lightweight cloth as used for row covers with vegetables, can provide protection from the few insects that may bother the developing mushrooms, as well as squirrels and chipmunks.  The most common problem is slugs.  There are many less toxic controls than poison slug baits, including rolls of moist newspaper (which slugs hide in by day and you can discard), saucers of beer (which attracts them, and they drown), or simply gravel under the logs which keeps the area less moist and so less attractive to slugs. 
           
Shiitake mushrooms may be ready for harvest in 7 to 10 days from shocking, longer if cool weather.  Most yield is in the second and third years, with one quarter to one half pound per log typical.  Harvest when the “gills” underneath are visible, and the outer edge is slightly curled under.  If the edge is flattened out, the mushroom is overripe but still edible.  Either twist off, or make a clean cut with knife to lessen bark damage.  Merely brush off dirt, but don’t wash. They should go into refrigeration within an hour of picking.
           
Mushrooms can be used fresh, frozen, or dried.   If kept cool (41 degrees F), dry, and dark, they can remain fresh for several weeks.  Use a paper bag, not a plastic bag nor airtight container.  For freezing, first soak in a solution of one teaspoon lemon juice to a pint of water, for 5 minutes.  This reduces darkening.  Then steam slices or quarters for 3 minutes, whole for a little longer.  Cool, drain, and place in freezer storage bags or containers.
           
For drying, remove stems, then place them on trays, bottoms (gills) up.  In a dehydrator, they should be dried until they are light but still flexible.  In the oven, they will need to dry on low heat (200 degrees F, with the door ajar). Once dried and cooled, store in plastic bags in a cool, dark place.   Reconstitute dried mushrooms by soaking in hot water for 20 minutes.

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