Growing Mushrooms with Hydrogen Peroxide--Updates

As I gain more experience and become aware of new information, I continually find that I need to make small changes to the peroxide manual to keep it in line with my current understanding of the effective use of the method. If I find significant pitfalls in a previously published procedure, I will let you know about it here. I will also post some news of advances in the procedures. Of course, new editions of the manual will generally contain additional material that has not been posted here.

This page is also evolving into a place for me to post announcements, such as new product offerings or new developments with the web site. So please check back regularly.

Go to Updates to the Third Edition
Go to most recently posted updates
See list of photos of peroxide method

Updates to the 2nd Edition:

1) I now pressure cook agar medium for only 20 minutes, to avoid carmelization, and I have reduced the nutritional richness of the MYA medium I use, to avoid excess production of toxic metabolites by the mycelium. I have essentially cut the recipe for MYA medium in half, except for the malt powder, for which I now use about 12 gms per liter. Be sure to use light or extra light malt extract, to avoid carmelization products. These changes do not materially affect peroxide usage--they are just better for the long term health of the mycelium than what I originally presented.

2) My success rate for clean grain spawn (soft winter wheat) is now running close to 99%. However, after a relatively trouble-free period with bulk substrate, I had a rise in contamination of pellet fuel cultures of P. eryngii and H. erinaceus which I reported on my web page. This problem has now subsided. This may have been the result of a leak in my pressure cooker, giving me poor sterilization of my nitrogen supplements, but I also took steps to insure complete mixing of peroxide into the substrate, and to avoid having bits of pellet fuel falling out as I filled bags, then bouncing off a nearby surface and falling back into the bag.

In addition, I recently discovered that particulates were coming in with my tap water, which increased with the onset of the rainy season. Of course, all water used without pressure sterilization needs to be clear and free of particulates, which can carry peroxide-decomposing enzymes.

Finally, I discovered that small bits off sawdust were lodging on the outside of my 5-gallon bucket near the rim when I opened or closed the lid. These bits could then pick up contamination, after which they could fall into my final substrate bags as I poured the sawdust from the bucket. Now I try to watch for these bits of sawdust and brush them off before I fill each bag with substrate.

I now seal all my bulk substrate bags by tying off with twist ties. It turns out that H. ulmarius, H. erinaceus, and P. eryngii can all reach primordia formation in bags that have been sealed in this way, with no microporous filter. However, although I thought at first that this success was due to oxygen supplied by peroxide decomposition in the substrate as the mycelium grows, it now turns out that there must also be oxygen diffusing through the plastic bags themselves (since the mycelium will not grow in tightly sealed plastic buckets). So--If you use plastic trash bags to hold bulk substrate, as suggested in the manual, try to get the thin (0.5 mil or less) bags made of high-density plastic rather than the more common bags made of soft, thick plastic. The thin bags will allow better oxygen diffusion. And the thicker bags are most likely PVC, which may release endocrine-disrupting chemicals into the mushroom substrate. Also, I have been told that some of the thicker bags are impregnated with fungicide.

I have also recently concluded that the procedure for "cleaning" mycelium of occult contaminants is more important than I previously thought, and to assure successful cultures it should be performed regularly (at least every third transfer, or every transfer if you leave your agar cultures for a long time between transfers). This is true whether or not you are using peroxide in your final bulk substrate, but it is especially important if you are not. Be sure not to cut all the way through the agar when you remove agar wedges for inoculation from a bottom-inoculated plate. Also, it is a good idea to wipe counter tops and fingers with rubbing alcohol before performing the procedure.

3) It was brought to my attention that, when I talk about hydrogen peroxide as being safe and environmentally benign, I should say that I am specifically referring to peroxide at a concentration of 3% or less. Higher concentrations, such as 30%, 35%, and 50% are available, but these are quite hazardous.

Updates to the 3rd Edition

Here are some changes that I have made since I released the 3rd Edition of the manual, Growing Mushrooms the Easy Way in February, 1999. (For new users of the manual, I recommend also reading through the Updates to the 2nd Edition, since some of these did not actually get incorporated into the 3rd Edition.)

It turns out the procedure for 10 Minute Spawn works best with pellet fuel made of light woods. Both fir and cottonwood pellet fuel have given me consistent success. When I tried oak pellet fuel, however, the pellets took a long time to disintegrate into sawdust on makeup, and I began getting many contaminated jars, presumably because the greater density of the oak sawdust slowed the heating and cooling process. It may be possible to compensate for these problems by increasing the amount of peroxide used.

I have at last succeeded in fruiting Agaricus subrufescens, the almond mushroom, on pellet fuel substrate (especially fir, but also cottonwood, and to some extent oak) prepared by the peroxide method. This mushroom seems to like a firmly packed sawdust substrate. I grow 6-7 lb blocks of mycelium, then combine 3 or 4 of the blocks into a larger culture (in a trash bag placed inside an apple box, for instance). The larger culture gets a 2 inch casing of 50:50 soil:peat with a handful of gypsum and enough vermiculite added to give a friable texture. Then I place the whole thing in warm spot, sprinkling the casing regularly, until the mycelium begins to show at the surface of the casing. Finally, I remove the box to a cooler spot, with plenty of air and some light, to allow the mushrooms to form. The yield so far has been small, just two pounds of mushrooms from an apple box of colonized substrate, supplemented to about 0.4% nitrogen. (Note added later: Yield seems to be improved by leaving the culture in a warm spot through the fruiting process).

A caution with processed supplements to be used without autoclaving: be careful that these supplements don't spoil in storage (or haven't already spoiled slightly when you get them). If they do, they will start to cause your peroxide to decompose, even if you pasteurize them. Keep them stored in a cool or cold place, and check them periodically by dropping some into a small amount of straight 3% peroxide solution. If they fizz, you won't be able to use them anymore without autoclaving them first.

Although I've used oyster shell lime for a long time, I recently found that this additive--after prolonged storage--can cause a low level of peroxide decomposition. Therefore, I now recommend ground limestone. If you can't find ground limestone, you can use hydrated lime (Mason's lime or builder's lime), but about half as much as you would use of limestone. I currently use 1 oz hydrated lime for 8.5 lbs of oak pellet fuel to make substrate for Hericium or elm oyster. Please handle hydrated lime with caution: it can burn skin, eyes, and mucous membranes. Do not use Dolomite lime, as it contains magnesium, which can inhibit mushroom development.

December 24, 1999: I've recently found that an overnight soak in vinegar can inactivate the peroxide decomposing enzymes in a sample of mycelium. Presumably other weak acids will have a similar effect. This may eventually prove useful in inactivating the enzymes that break down peroxide in raw drainable substrates like woodchips, cottonseed hulls, straw, or other agricultural wastes (as well as supplements like millet), so that they can be prepared with peroxide without prior pressure sterilization.

December 29, 1999: Experimenting with a sample of commercial birdseed, I find that an overnight soak in vinegar does not eliminate the peroxide-decomposing enzymes in the seeds. But 15 minutes of boiling the seeds in ten-fold diluted vinegar eliminates nearly all the activity of the enzymes. Apparently the boiling allows the vinegar to penetrate the tough seed capsules.

January 12, 2000: Happy New Mycelium!

On storing and drying agar plates: I've recently learned that the biggest factor causing decline in peroxide concentration in unused agar plates is probably evaporation of the peroxide. So if you dry your plates for a long time after pouring, or if you store the plates for a long time, you may get more contamination than you expect. This problem can be avoided by increasing your initial peroxide concentration slightly (if you expect to dry or store the plates for a long time), or by drying the plates for shorter periods. When storing plates, be sure they are sealed in an air-tight container or plastic bag.

On oyster shell lime: I've recommended against using oyster shell lime because it can "spoil" and develop peroxide-decomposing enzymes that will cause contamination in cultures. Now I find that fresh oyster shell lime has even more peroxide-decomposing enzymes than oyster shell lime I've stored for a long time. But there is a remedy: if you bake the lime in the oven (with plenty of ventilation!) at 400 degrees F for an hour, you can destroy the enzymes. Then you can freely use your baked oyster shell lime with any of your peroxide procedures.

February 3, 2000: Here are some pictures of what I do with my pellet fuel substrate. Nothing remarkable here, but I'm starting to generate a few "visuals" to go with the otherwise pictureless manual.

Balloon test for peroxide concentration
Measuring oxygen from peroxide decompostion
Cutting agar to transfer mycelium
Inoculating mushroom spawn
Inoculating a bucket of substrate
Filling a bag with inoculated substrate
The substrate sealed in a bag, inside a box
Jars of Ten Minute Spawn on a bookshelf
Some mushroom growing equipment
Pouring agar plates

February 8, 2000: To help with locating some of the supplies called for in the peroxide manual, I have set up a "Sources" page. Unfortunately, this page right now will mostly be of help to residents of the US, although any information contributed from other countries will be gratefully added. Visit the Sources page

March 9, 2000: I've added some more contact information for Springfield Scientific supply on the Sources page, and corrected the phone number listed there for Pennington Seed.

A note on testing materials to see whether they are peroxide-compatible or whether instead they contain peroxide-decomposing enzymes: for the most sensitive test, add a little detergent to the peroxide. Then any bubbles that develop will appear as foam. Also, the detergent will help to wet the material, allowing the enzyme reaction to develop sooner if it is going to develop at all.

March 22, 2000: For those of you who want to inoculate peroxide-treated bulk substrate with commercially-produced (non-peroxide) spawn, doing this does not create a problem: the latest information I have is that the non-peroxide spawn grows easily into the peroxide-treated substrate without any appreciable lag to adapt to the peroxide.

April 5, 2000: There is apparently an ambiguity in the manual regarding the amount of water I use for preparing pellet fuel substrate. To clarify, I use roughly 7 quarts (or 7 liters) of water total for about 9 pounds (4 kgs) of oak pellet fuel, the water divided in half for the two stages of substrate preparation.

June 5, 2000: I've found that the distilled water storage method described in the manual is not as effective for long term storage as I had once thought. I have not been able to revive mycelium of P. eryngii, H. ulmarius, or A. subrufescens that I've stored for two years in distilled water. Therefore, I have to recommend that this method only be used to store mycelium for six months for most species (I was able to revive Hericium erinaceus after about 2.5 years of storage). Unfortunately, there seems to be no perfect storage method--even liquid nitrogen does not work in every instance.

June 20, 2000: I've added a couple of substrate ideas to the Sources page for people who live in the UK or nearby.

July 24, 2000: Kiln-dried sawdust (that is, sawdust produced by the milling of kiln-dried lumber) can now be added to the list of likely peroxide-compatible substrates. A sample of this kind of sawdust that I tested for peroxide-decomposing enzymes showed only very slight activity.

August 10, 2000: Just released! Volume II of Growing Mushrooms the Easy Way. Click on the title to find out what it contains.

September 30, 2000: A tip on cloning mushrooms: use the youngest mushrooms you can get, for rapid mycelium formation.

When preparing mushroom substrate for the peroxide method, be cautious about adding fertilizers or nitrogen supplements that contain added trace metals, especially iron, manganese, and copper. These metals will speed up the decomposition of added peroxide.

November 17, 2000: The new 3rd Edition of Paul Stamets's text, Growing Gourmet and Medicinal Mushrooms has been released! It can now be ordered through my link to (click on the title). This new edition has been expanded by over 150 pages compared to the 2nd edition, with new chapters on Agaricus blazei (Royal Sun Agaricus), Agaricus brunnescens (Portobellos), Sparassis crispa (cauliflower mushroom), and more.

January 2, 2001: I've recently learned that Mason's lime or hydrated lime is a form of dolomite lime, and as such, it contains more magnesium than is likely to be optimal for mushroom growing. So I shall have to reverse my earlier suggestions for using hydrated lime for a pH correction in sawdust-based medium. Apparently it is better to use either ground limestone if you can get it, or oyster shell flour. The latter has to be baked for a couple of hours at 400 degrees F to assure that it does not contain peroxide decomposing enzymes.

Another enzyme-free commercially available wood chip product can be added to the list of peroxide-compatible substrates. It is called Beta-Chip™ and it is a lab-rat bedding made of1/8 inch maple chips by a company in New York. See the Sources page for more info, and thanks to Michael Joy for bringing this to my attention.

January 21, 2001: Apparently I've missed putting metric conversions on a few measurements here and there in the manuals. For future reference,
1 quart = 0.95 liters
1 cup = 235 mls
1 tablespoon = 15 mls
1 ounce = 28.35 grams

I've added a scientific supply house in the UK to the Sources page.

January 30, 2001: When testing new substrates or supplements for peroxide-decomposing enzymes, it is not necessary or advisable to use peroxide concentrations higher than 3%. You may get confusing results if you use peroxide that is concentrated enough to oxidize the substrate and release carbon dioxide. So stick with 3% peroxide for testing enzymes.

A further note on hydrated lime: I've now found out that certain brands of hydrated lime do not contain magnesium above a fraction of a percent. These should be acceptable for mushroom growing. Take home message: check the composition figures on the package!

February 14, 2001: It was brought to my attention that my recipe for MYA medium calls for 5-7 wood fuel pellets per liter, but these pellets may vary in size in different parts of the world. So, for the record, that quantity of my pellets weighs about 0.15 oz, or 4.25 grams.

February 27, 2001: I have added a supplier of oak pellet fuel in Arkansas, with an outlet in New Mexico, to the Sources page.

March 3, 2001: A few days ago I posted information on the use of millet as a nitrogen supplement, and pelletized straw as a substrate. I have since decided these postings were premature and need further evaluation. Stay tuned.

March 8, 2001: I've posted a few more photos to the photos list. Most of these photos are also now organized into a Slideshow, with somewhat more commentary, accessible from the Main Menu. And by the way, if any of you want to contribute photos, please let me know. They need to be a modest size for fast loading--I don't have photo manipulation software to reduce the files.

June 6, 2001: I'm happy to announce that pelleted straw (sold as an animal bedding in some areas of the US) can be used successfully as a substrate for the "Add-and-stir" protocol with the elm oyster mushroom. To use this material, the peroxide concentration needs to be roughly doubled compared to that recommended for pellet fuel in Volume II. Pelletized straw contains some detectable peroxide-decomposing enzyme activity, but the level is low enough that the higher peroxide concentration can compensate for the resulting peroxide decomposition. I have tried this only with elm oyster mushrooms, although Pleurotus species should work as well, and other species deserve to be tested. Pelleted straw should be a nice addition to the list of workable substrates, since it takes up much less space than straw for storage and for cultures, it doesn't need chopping like straw does, it has a fine texture like sawdust for mycelial growth, and it is made from an agricultural waste product that isn't derived from cutting forests. See the Sources page for the name of one supplier. Thanks to Andy Kayzek for providing me with a 10 lb sample of pelleted straw from this source to experiment with.

I have also learned that cottonseed hulls can be used successfully as a substrate for oyster mushrooms, including P. eryngii, with the room-temperature straw protocol in Volume II, provided the hydrated lime alternative is used. Thanks to Michael Joy for this information.

Finally, I've added some information on peroxide and on kiln-dried sawdust to the Sources page.

August 6, 2001: It has been pointed out to me that there is an error in the recipe for MYA medium both in Volume 1 and Volume 2. The amount of agar and malt powder should be the same in ounces (0.42 oz) as well as in grams (12 grams). Fortunately, this makes little difference for the growth of mycelium.

Also, I have been urged to remind people that cotton, not being a food crop, is often sprayed with pesticides not approved for use on food. Therefore, cottonseed hulls may well contain residues of pesticides you might not want in your substrate. On the other hand, fungi can often break down such chemicals and render them harmless, so we won't know the real result of growing mushrooms on pesticide-laced cottonseed hulls until someone tests the mushrooms for their pesticide content.

December 3, 2001: I have recently begun shipping an expanded and revised 2nd edition of Volume II of Growing Mushrooms the Easy Way. Click on the title to find out what the new edition contains.

December 29, 2001: I ran into difficulty getting my mushroom strains to grow on gray cardboard from a couple of sources (see Volume 2), but Michael Lim reports excellent results using egg carton cardboard.

February 27, 2002: Bill Chalmers of Western Biologicals tells me that casing soil (page 33-34 of Volume 1) for Agaricus mushrooms should not contain gypsum, as it drives the pH down in interaction with metabolites of the mycelium. This will lower the ultimate yield of mushrooms. Bill says that calcium carbonate is the preferred source of calcium in casing, as it buffers the pH upward.

J. Croskey reports that shavings and sawdust from kiln dried wood may sometimes contain fungicides or preservatives. This will probably be true most often when the wood is intended for exterior use. Obviously, such material will not support mushroom growth.

I have received reports of problems using the straw protocol with rice straw. I am consulting with the growers involved to try to determine the source of the difficulty and develop a remedy. If any of you are successfully using peroxide with rice straw, please let me know. Thanks.

April 12, 2002: L Gehrken reports success using the peroxide protocol with rice straw (roughly 20% moisture content before treatment) if the soaking period is reduced to just 1.5 minutes. Apparently rice straw is far more absorbent than wheat straw, and it gets too wet with longer soaking.

H. Hajj writes that peroxide can be rapidly decomposed for the balloon test by adding a small crystal or two of potassium permanganate. Lightly wrap the crystals in a bit of tissue paper so that they will not fall into the peroxide solution until you have your balloon in place. Warning: because of potentially violent reactions, don't use potassium permanganate with peroxide concentrations higher than 3%--always dilute your solution first if it is more concentrated than that.

A. Janjigian says that corn gluten sold commercially as an organic herbicide (pre-emergence weed-killer) will work well as a nitrogen supplement for the peroxide method. Although it is not necessarily cheap, it is easier to obtain in the US than the Sylvan resin-coated corn gluten supplement, CG60. One brand name is "Concern" and a similar product is sold by Gardens Alive (

August 20, 2002: I've added some additional information on bags suitable for cultures to the Sources page.

March 12, 2003: I've added information on sources of laboratory supplies, and sources of pellet fuel, with a link to an online pellet fuel dealer-locator, on the Sources page.

July 1, 2005: I've added information about an additional online source of agar, and a circle-cutter that can be used to cut cardboard circles for jar lids, on the Sources page.

January 2, 2006: It occurs to me that I have not sufficiently emphasized in my manuals an important point concerning the use of the peroxide method with commercial cultures of mycelium. This point arises from the following consideration: for mushroom mycelium to grow in the presence of peroxide, it must be adapted to peroxide at a low concentration, usually by incubation of a sample of mycelium on peroxide-treated nutrient agar for a period of roughly two weeks. Without this adaptation process, peroxide will strongly inhibit or even kill mycelium at the concentrations used to prepared bulk substrate or spawn. But when properly adapted, the mycelium grows freely in peroxide-treated substrate. Now the important point to understand is that spawn sold commercially has not been adapted to peroxide, so it will normally fail to thrive when inoculated directly into peroxide-treated substrates such as wood pellet fuel prepared by the methods in my manuals.

There are certain exceptions to this rule, however. For instance, those materials which contain active peroxide-decomposing enzymes, such as straw and similar drainable "raw" substrates, can be pasteurized with a peroxide soak and then inoculated with commercial spawn. In these substrates, the peroxide will disappear by decomposition sometime after the grower drains off the soaking solution, allowing growth of the non-adapted mycelium in the peroxide-treated substrate.

"Cleaning the mycelium" is one of the routine operations ordinarily required for successful maintainance of mushroom tissue cultures with the peroxide method (see Volume 1). This procedure eliminates occult contaminants that tend to accumulate on the mycelium during normal incubation when unfiltered air can diffuse into the cultures. Now A. Janjigian reports that he has been able to avoid the need to clean his mycelium of occult contaminants for several years, by always inoculating his fresh plates with agar chunks placed mycelium-side down, and then carefully sealing the cultures with breathable plastic film such as Parafilm™ for incubation.

August, 2007: A couple of issues concerning the preparation of straw with peroxide and vinegar have come to my attention. One is that the procedure in Volume 2 assumes a 5% acetic acid content for vinegar, which is the standard for most vinegars in the US. There apparently are, however, pickling vinegars with concentrations of acetic acid as high as 28%, and if a vinegar of this kind is used in the preparation of straw, the quantity will have to be reduced: vinegar has anti-fungal properties when the concentration gets much above what I am assuming in the manual.

The other issue is that I have been assuming that you are using tap water with little capacity to resist changes in acidity or alkalinity (that is, little buffering capacity) such as my own water, so that adding the amount of vinegar I recommend for the straw soak will bring the pH of the water fairly close to the pH of the vinegar (4.5). But it has been pointed out that the tap water in some locations may contain dissolved carbonates that considerably increase the buffering capacity of the water. In that case, the amount of vinegar I recommend will not bring the pH down as it should. The difficulty here is that we cannot simply add more vinegar, because it may have anti-fungal effects at a higher concentration. Therefore, we will have to lower the pH with some other acid. Certain other acids are fairly available from brewing supply stores. I suggest trying phosphoric acid.

January, 2008: I have recently started a private moderated e-mail discussion group on Yahoo open to anyone who is an authorized owner of any of my mushroom-growing manuals. If you'd like to join, please visit to subscribe. (I will need you to identify yourself in a way that will allow me to find you in my customer records--thanks.)

R. Wayne

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  • This document Copyright: ©2006 by Randall R. Wayne, Ph.D. All rights reserved. No part of this work may be reproduced or used in any form or by any means without permission of the author.