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Growing Mushrooms on Logs and Stumps

by Fungi Perfecti

Following is a condensed version of the instruction booklet that accompanies our Mushroom Plug Spawn.

Cross-Reference Chart: Wood Type to Mushroom Species

Selecting Your Wood

Logs may be cut for Plug Spawn inoculations at any time during the year. However, for best results, we recommend cutting your logs in late Winter/early Spring just before tree buds sprout. This is when the sap and moisture content in the wood are highest. The mushroom mycelium will feed on the sugary sap and moisture during the colonization period. Higher moisture and sap content equates to more food for the fungi.

Our hardwood species prefer deciduous trees types such as Oak, Poplar (Cottonwood), Elm, Alder, Maple, and other similar woods. Fruit woods, such as Cherry or Plum, should generally be avoided, as they tend to be too dense for all but the most aggressive species, such as the Tree Oyster and Turkey Tail. Thick-barked hardwoods are preferable over “paper-bark” woods such as Birch and Cherry. Eucalyptus has proven to be highly suitable for Shiitake. Logs that have damaged bark or are shedding their bark should not be used. Some species of wood such as Sycamore and Madrone tend to shed their bark quickly after cutting, making them less suitable for log cultivation of mushrooms.

Our softwood species prefer coniferous softwoods. We suggest Spruce, Hemlock, or Fir. We do not recommend Cedar, Cypress, and Redwood as they have anti-fungal compounds that can inhibit the growth of fungi. There are a few Pine species that are suitable for certain mushroom species. Please refer to the growing parameters listed with each mushroom species for more information.

Your logs and stumps should be clean, healthy, and free of any other fungi (as they can compete with the new fungi you are trying to establish). Your logs or stumps should also have all of their bark intact. This is especially important to aid in water retention and to help protect the inoculated fungi from parasites and competition from other native fungi. The logs should be cut from a healthy, live tree. If you do not want to cut the whole tree, trimming large limbs is acceptable. The ideal log size should be 3 to 4 feet in length and 4 to 8 inches in diameter. The larger the diameter, the longer it will take for the mycelium to fully colonize your log.

For stump cultivation, we recommend using the same wood type guidelines described above. Once the stump is cut, we suggest girdling the base (removing bark from the bottom 2 inches of the stump), this will ensure that the stump does not continue to grow after plugging.

As with the logs, your stumps should sit for at least 2 weeks, but no longer than 6 months prior to inoculating. Be sure the stump will be mostly shaded: sunny conditions are not ideal for mushroom cultivation. If the stump is not shaded you can offer it shade by putting up a shade cloth.

You are now ready to begin the plugging process!

Equipment Needed

You will need the following equipment. Gather these materials before opening your Plug Spawn:

  • 516" drill bit (to drill the correct diameter hole)

  • High speed drill (for drilling)

  • Rubber mallet (for tapping the plugs in the holes)

  • Beeswax or a soy-based wax (e.g., cheese wax) for sealing your logs or stumps

  • Camping stove, electric hotplate or other way to melt the wax

  • Old metal coffee can or other container in which to melt the wax

  • Small 1 inch paint brush (to apply the wax)

The best time to plug your logs varies depending on your location. The general rule of thumb is to inoculate when you’re not experiencing extreme weather conditions, such as snow/ground freezing, or heat waves. Mid-Spring is generally a good time to do your inoculations (after the threat of freezing temperatures has passed). If you have a protected area in which to place your newly inoculated logs, such as a garage, root cellar, shed, barn, or other outbuilding, feel free to plug logs all year round. Keep in mind the logs will need moisture during the incubation/colonizing process. If storing the logs in an outbuilding, make sure you have an adequate way of watering the logs.

Now to begin plugging!

Procedure

Drilling Your LogsStep 1: Using a 516" drill bit in a high-speed drill, drill 114" deep holes. (To insure accuracy, you can install a collar stop, or use duct tape or similar tape to create a tape stop) The holes should be no more than 4" apart, and in an evenly spaced “diamond” or “checkerboard” pattern around the log. You should be able to drill 45 or more holes per 3–4 foot log.

If inoculating stumps, the holes should be drilled along the circumference of the face of the stump, in the area between the bark and heartwood (called the sapwood). You should be able to drill 30–50 holes per stump.

Step 2: Once the holes have been drilled, it is time to insert the plugs. Now you can open the bag of Plug Spawn. With clean hands, remove one dowel from the bag (you may have to break it apart from the rest) and place the bottom of it into your first hole. If it seems a little on the tighter side, that is ok. Grab your rubber mallet and gently, but firmly, pound the plug into the hole. The top of the dowel should be flush with the top of the bark on the log. Repeat this for all the holes you have drilled and don’t leave any drilled holes empty.

Step 3: Once you have inserted dowels into all of the holes you have prepared, it’s time to seal your log or stump with a food grade wax. This step is highly recommended to ensure a higher success rate for your logs. Waxing will help retain moisture and prevent the invasion of parasites and competitive fungi.

Step 4: Once you have melted the wax, take your paint brush and dip it into the wax. You do not need a lot, just enough to create a sturdy seal. Using the paint brush, apply wax to both ends of all of your logs (you can also dip the ends of your log into your wax if the container size allows). Once the ends are waxed, seal over the holes containing the Plug Spawn dowels. Brush enough wax over the plugged area to completely cover the hole. If sealing a stump, we recommend sealing the entire face of the stump. Seal any exposed wood, or “wound areas” on the log or stump, as exposed wood leaves the logs vulnerable to parasites and competitive fungi. If you run out of plugs and have empty holes, seal those with the wax as well. Do not, however, completely cover the entire log with wax; moisture still needs to penetrate into the log through the bark.

Caring for Your Logs: Incubation

Tarped RickOnce your logs and stumps are sealed and the wax has hardened, it’s time to position your logs for incubation. The logs should be placed so they are off the ground, on pallets, cinder blocks, or other logs. We do not recommend incubating your logs in direct contact with soil. Logs should be stacked in crisscrossed piles called “ricks” to help conserve moisture and space. The ricks should be located in a moist, shady area under dense forest canopy or shade cloth. You can also store your logs in an outbuilding (as described in the Procedure section above). We recommend keeping logs inoculated with different mushroom species separate so cross-species competition does not occur.

It’s important that sufficient moisture is maintained to support the growth of the mushroom mycelium. Water your sealed logs once or twice every other week for 5–10 minutes at a stretch until freezing temperatures or heavy rains begin. You only need to water them when they are not getting regular moisture. If you live in an arid environment you will need to water more frequently, approximately 1–2 times a week.

You can help with moisture retention by covering your logs or stumps with a sheet of burlap or shade cloth. Place boards or similar braces on top of your logs under the material to keep it suspended 2–4 inches away from the logs. Do not use plastic to cover your logs as this will encourage mold or bacteria to form on your logs.

Now that the hard part is done (plugging, watering, and covering) the next step is to wait. Your logs or stumps are now in the process of incubating and will require 6–12+ months for the mycelium to fully colonize the wood. The length of time needed for colonization depends on the species of mushroom, wood type, and the size of the log. Smaller diameter logs (4–6 inches) will colonize more quickly compared to larger (8+ inch) logs.

Log EndsDepending on the wood type and diameter of your logs and the species of mushroom you are cultivating, your logs may be ready to fruit in as little as 6 months (refer to the parameters for each mushroom species for “normal” incubation times for each species). The longer you wait to “force fruit” your logs, the greater the level of colonization. Preferably, we recommend waiting 9–12 months before attempting to initiate your logs for fruiting (possibly longer if you used a denser wood like Oak). Visually check if the log is ready to fruit by looking at the waxed cut face of the log. When sufficiently colonized, you should see a “mottling” pattern covering approximately 65% of the end of the log, as shown in the image to the right.

Fruiting Your Mushroom Logs

Once you have determined enough time has passed and your logs or stumps are sufficiently colonized to support mushroom production, it’s time to initiate the fruiting process. Each mushroom species has a different temperature requirement to fruit. Please refer to the growing parameters listed with each mushroom species for more information.

If your logs look ready to fruit and they aren’t already producing mushrooms, we recommend submerging the logs or stumps in a tank or bathtub of water for 24 hours. We also recommend using non-chlorinated, non-distilled water. Options include well or rain water, boiled tap or spring water. If your only option is chlorinated tap water we recommend filling a tub or some buckets and letting them sit overnight to dissipate the chlorine. Please note: If you incubate your logs in a naturally wet area, they may begin fruiting on their own. Check your logs for primordia (baby mushrooms) forming before you soak them. If mushrooms are already forming, do not soak your logs; instead, treat them as if they have already been initiated.

After soaking, your logs can be partially buried for fruiting. Depending on the species they will be buried horizontally or vertically with a buffer of sand or gravel to help in retention of moisture. We do not recommend burying your logs in soil as this will cause the logs to rot more quickly, resulting in a shorter life span and fewer mushrooms. Dirt/soil can also contain bacteria or other organisms that may be harmful to your fungi. When burying logs horizontally, they should be buried so the top third of the log is above the surface. When burying vertically, you can bury the bottom 1⁄3–2⁄3 in a large black gardening pot or directly into the ground (with the sand or gravel buffer). It is important that the logs receive adequate moisture during this stage as it will aid greatly in the production of primordia (baby mushrooms). They should be watered 1–2 times a day if you are not having regular rain fall, or you live in a dry, arid environment. If you live in a moist area, you may only need to water your logs or stumps every couple of days when you’re not getting rainfall.

Primordia should start forming within 2 weeks of initiation. Mushrooms can, and will, form all over the log, not just from the holes containing the Plug Spawn. Each mushroom species will mature at a different rate.

Fruiting Shiitake Log
Photo credit: Jim Gouin

Important note: NEVER eat a mushroom unless you are sure of its identification. The first time you eat any mushroom new to you, consume a small portion and wait 24–48 hours. If no undesirable effects occur, you may safely assume that you do not have an allergy to this mushroom. A small percentage of the population (an estimated 1–2%) is “allergic” to mushrooms, that is, their bodies can not produce the enzymes necessary to digest them. They typically suffer temporary, albeit unpleasant, gastrointestinal discord. We recommend that all mushrooms be cooked before they are eaten.

After you have harvested your first flush, the logs will usually lapse into a period of dormancy (a resting period). If they do not fruit again immediately after the first flush, let them sit for 2–3 weeks before re-initiating them. If the temperatures have gone outside of the “preferred fruiting temperature” ranges listed in the Mushroom Species descriptions at the beginning of this booklet, you will want to wait until the temperatures are back within the desired ranges before attempting to fruit the log or stump again. In most cases, they will fruit once the temperatures are favorable; just make sure the logs retain adequate moisture.

For more information about log and stump cultivation, please refer to Mycelium Running: How Mushrooms Can Help Save the World, by Paul Stamets (Chapter 11, pages 172–186).

Like many other endeavors, log and stump cultivation of edible fungi requires patience, time and a little luck. We trust you will find your experience will be an enjoyable and “fruitful” one!

The Folks at
Fungi Perfecti

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