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By Admin (Admin) on Thursday, August 23, 2001 - 12:02 pm:

The Compost-o-matic

By: Oily Discharge

In the event that one desires a small amount of mushroom compost done in a precise fashion, the compost-o-matic described here gives excellent results. This method uses a styrofoam picnic cooler with a steam humidifier and a common light dimmer (or variable transformer) to control the steam and compost temperature. The final product is about 3 gallons of pure pasteurized compost in just 6-7 days. Total cost for the bits and pieces to construct a compost-o-matic should be no more than $25 (U.S.)

Materials required for the construction of a compost-o-matic:

Styrofoam cooler

Steam humidifier or vaporizer (Vicks warm mist or similar)

Glass jug, one gallon or larger

2 foot of hose that will fit jug mouth or cap

5 wood sticks, 2 foot long

Single pole, solid-state dimmer switch

4 sq. ft. of metal screen, ¼" or 1/8" mesh

Long stem thermometer, ³ 120° C, scientific or kitchen (meat therm.)

The construction of the compost-o-matic utilizes a styrofoam cooler, preferably close to 14 inches by 22 inches by 15 inches deep in size. Six ¾" holes, evenly spaced across the surface of the lid, are melted with a soldering iron or cut with a knife. Six more holes of the same size are melted or cut into the body of the cooler, three along each side, two inches up from the bottom edge. On the short sides of the cooler body, one hole is cut or melted on each side at the bottom edge. One of these holes is sized ½", and will serve for drainage. The other end has a hole ¾" wide by 2½-3 inches deep to accommodate the steam output head or nozzle of the steam humidifier.

The bottom of the cooler is lined with aluminum foil, being careful to not obstruct the drain or steam inlet. A screen support is made from ¼" or 1/8" screen or hardware cloth. The screen is cut 8 inches larger than the dimensions of the bottom of the cooler. 4 inches of screen are folded 90° at each edge to form supports, which hold the surface of the screen 4 inches above the bottom. The compost sits on the top surface of the screen so that the steam can flow evenly underneath the compost. This screen support should fit the bottom of the cooler without large gaps around the edges.

A single-pole solid-state dimmer is placed in circuit to control the humidifier power. Good wiring and insulating procedures need to be followed. If you aren't knowledgeable about wiring, find someone who is to help. It is important for safety that the wiring be correctly installed. The best method is to wire the dimmer switch (in a plastic electrical switch box) to a standard outlet (in a plastic electrical box) and connect to power using the cut-off end of a suitable extension cord. Simply plug the humidifier into the dimmer-controlled outlet. Of course, someone who cuts corners will just cut the humidifier cord and splice the dimmer switch into the cord. You're on your own if you use that method. Things to check for:

1.The maximum capacity of the dimmer switch (in watts) should be greater than the load imposed by the humidifier. (almost all dimmers have the necessary rating)

2. The wiring methods should be well insulated and suitable for the damp environment it will be used in.

Finally, a water reservoir is constructed. Arrangements are made to secure a one-gallon or larger glass water jug above the humidifier. A 1½-inch hole is cut in the top surface of the humidifier body to accommodate the hose. The humidifier is filled with water to the "fill" line, and the hose is inserted so that the open end of the hose hangs ½ inch below the fill line. In this way a constant level of water is maintained in the humidifier, which makes the steam output constant for a given dimmer setting. This is important to maintain accurate steam/temperature settings during a composting run. During a run, the humidifier electrodes must be cleaned at least every other day, or output will be seriously effected. A slightly expensive option to regular cleaning is to use distilled water.

Before the first time a compost-o-matic is used, it is best to set it up where it will be used. Tape all the holes closed except the drain hole and the humidifier nozzle hole on the bottom. Fill up the humidifier and reservoir jug with water and turn on the humidifier at full power dimmer setting. Allow the cooler to steam for 4 hours or so to eliminate any plastic or chemical odors and to test operation.

To begin a compost run, mix in a bucket, approximately 2½-gallons of shredded straw with 1 gallon shredded dry fresh manure, cow or horse. Mix in 3-4 ounces cottonseed meal or 1-2 ounces blood meal (nitrogen sources, available at most plant nurseries). Add 3½ quarts of hot water, preferably with a sprayer, and mix thoroughly. This warm mixture is loaded into the cooler without delay, loosely filling the cooler to within 1-2 inches of the top. Five sticks are placed in the cooler before adding the compost mixture, so that after the compost is loaded, 2-inch square ventilation shafts can be created by wiggling each of the sticks around. The sticks are withdrawn, and the lid put in place, all the vent holes are taped shut except the one on the lid furthest from the steam nozzle, and the dimmer set on maximum. The thermometer is placed through the untaped hole so that it is measuring the middle of the compost.

During the first phase of the run pasteurization occurs, killing all insect life. Note that this is opposite of how it is done at a commercial mushroom farm or in outdoor nature composting, where pasteurization is done at the end of a composting run. After about 2 hours of full power steaming, the temperature should rise to approximately 65° C (60° -70°). Quoted temperatures are only a rough guide, try to maintain the temperatures within the given ranges. For this first phase it is necessary to reach a minimum of 60° C. Once the temperature reaches 60° C check the time and let the compost remain above 60° C. for 3-4 hours.

At the end of this time remove all the tape from the ventilation holes and leave the dimmer setting on full. Within a day ammonia will be noticeable in the exhaust steam and the temperature should be 55-65° C. Hold this temperature for 2-3 days. After the first day the ammonia odor should disappear. After this happens, white fire fang, or actinomycete fungi, will be apparent in the compost. It is best to allow the compost run to proceed undisturbed, but if you wish to check it is okay to briefly lift the lid and move the compost surface. Don't allow the compost to cool during any brief investigations. At the end of the 3 days actinomycete should be prominent and there should be no ammonia smell. If not, extend the high temperature phase for up to an additional day.

The dimmer setting is now lowered slowly so that the compost temperature falls 2° -3° every 2-3 hours, until a temperature around 50°C is reached (45° -55°). The compost is then held at this lower temperature for 3-4 days. At the end of this time the power is turned off and the compost is allowed to cool slowly inside the closed cooler. It is ready to lay out and spawn when the temperature cools to 24° -28° C. It is best to spawn the compost immediately after it has cooled, although it can be stored for a few weeks if necessary.

The compost made in this way is usually excellent, comparable to the best commercial mushroom farm compost. An added benefit is that new compost recipes can be experimented with in small quantities and in short time frames. One extra is that the drain water makes an exceptional organic fertilizer for houseplants.


1. This document is based almost entirely on plans and text from Growing Wild Mushrooms by Bob Harris. Out of Print, published in 1976. Minor changes were made to include improvements made by this document's author. In particular, the inclusion of a solid state dimmer switch, which was not commonly available at the time of original publication, is new. The original plans recommended using a variable transformer, which is an uncommon, bulky, heavy, and expensive part.

2. The idea for small scale controlled composting was originally developed and published by James P. San Antonio, working for the U.S.D.A. in the 1950's & 1960's. Mr. San Antonio is also the mycologist that originated many of the early methods of fruiting Agaricus spp. on sterilized grain for laboratory study. His methods were adapted to grow Psilocybe mexicana when the first samples were made available by the Wassons, when they returned from their now epic visit with Maria Sabina in 1957. In the early 70's these methods were adapted for home use culturing Psilocybe cubensis by Oss & Oeric.

3. The formula for compost here is very basic. With trial and error many materials can be formulated into usable compost. In particular, it is important to mix for the correct carbon/nitrogen ratio (sacarides/protein). Any properly balanced mixture suitable for large scale composting is suitable for use in the compost-o-matic. Very useful tables of compost ingredients are included in The Mushroom Cultivator and Growing Gourmet and Medicinal Mushrooms, both by Paul Stamets.

4. Some species of mushrooms culture well on ordinary pasteurized straw with no additions. The compost-o-matic is ideal to pasteurize straw. It is much simpler and more accurate than immersion in hot water or other methods. Just load with shredded dried straw and pasteurize @ > 60° for 4-6 hours. Allow to cool slowly covered, and spawn when < 28° C. Typically the straw will be at proper moisture content when unloaded.

Happy shit-cooking,

Oily discharge

April 1, 2000

By Bluepowermilk (Bluepowermilk) on Tuesday, May 01, 2001 - 12:44 am: Edit

Could one use "Cow Manure" from Walmart for the dung teks described?

Its the stuff that comes in 40lb bags...

BTW...This place is the best. Been lurking since Quo got it up and running.

By Quote (Quote) on Tuesday, May 01, 2001 - 03:06 am: Edit

can't guarantee it though.
do a small test batch first.

By Bluepowermilk (Bluepowermilk) on Tuesday, May 01, 2001 - 03:50 am: Edit

More info...

The brand is Garden Basics. It comes in 40lb bags, and its stated use is "for enriching soil or as a top layer"

There was some of it open. It is black, and to my surprise, didn't smell like poo. It actually looked and smelled like, well, dirt

It didn't *say* composted on the bag anywhere, but believe it is. Otherwise, IIRC, would not in fact look/feel/smell like dirt (like jiffy mix) but in fact, like cow shit

Any help would be great...TIA

By Quote (Quote) on Tuesday, May 01, 2001 - 03:51 am: Edit

should work, after pasturization.
still, do a small test first.
some store brands work great, some suck.

By Fanaticus (Fanaticus) on Tuesday, May 01, 2001 - 07:10 am: Edit

that kind of "manure compost" is not the real deal. It is chemically treated and heated and dried. It is no good for shrooms at all if you use it by itself. You can get colonization, but you are not going to get any shrooms. If that were the case, people would be flocking to Whalmart to get that stuff. It is dirt cheap and good for gardens, but that's about it.


By Bluepowermilk (Bluepowermilk) on Tuesday, May 01, 2001 - 02:49 pm: Edit

thx for the info. what should one look for vis a vis price/description?

Thanks guys are great!

By H4e2m0p (H4e2m0p) on Tuesday, May 01, 2001 - 05:41 pm: Edit

what about "mushroom compost" from lowes? any luck with this, possibly mixing it w/ verm for a casing?

By Fanaticus (Fanaticus) on Tuesday, May 01, 2001 - 06:01 pm: Edit

"mushroom compost" is what is left from a mushroom farm. It is not for GROWING shrooms but to use as soil additive in gardens.

I visited a shroom farm once and they had a lot of spent compost. This is what is called "mushroom compost". It is no good for growing shrooms because it is used up as far as the fungi is concerned.


By Buck (Buck) on Tuesday, May 01, 2001 - 08:25 pm: Edit

they got a 6 foot pile of cow shit at my work, would i have to do anything special besides pasturizing it to use it ?

By Quote (Quote) on Tuesday, May 01, 2001 - 08:26 pm: Edit

make sure it's been composted, which basically means well aged. too fresh will not work.

By Remora (Remora) on Tuesday, May 01, 2001 - 10:17 pm: Edit

They had a 6 foot 7 inch pile of shit where I used to work, too. His name was... nevermind.

Sorry for being off topic, I couldn't help it.

By Rochester (Rochester) on Wednesday, May 02, 2001 - 04:38 pm: Edit

Remora that was FUNNY!

By Oldtimer (Oldtimer) on Wednesday, May 02, 2001 - 05:29 pm: Edit

Buck... Check out the Compost-a-matic article in the Archives. This method really works and turns out great compost in about a week using manure. I've used this styrofoam ice chest/vaporizer rig many times and it always produces top-notch substrate for cubensis.

By Fungusflipper (Fungusflipper) on Thursday, May 03, 2001 - 04:31 am: Edit

so is the composted/pasteurized manure used for substrate or casing?


By Quote (Quote) on Thursday, May 03, 2001 - 01:43 pm: Edit

similar to a casing, but it provides some nutrients, like a substrate