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Perlite Humidification FAQ
version 1.3, 01/05/00


This FAQ is presented for informational purposes only. We do not advocate illegal activities but we do believe in the right of the individual to have free access to information and ideas. We strongly recommend that the reader learn about applicable local and federal laws regarding possession, production, and sale of any mushrooms that they intend to grow whether using this or any other method. This FAQ may be copied as long as it remains intact with all credits attached.

The information contained in this FAQ has been culled from a variety of sources. As far as I know, the idea to humidify with perlite first started being tossed around early in 1996. It's a pretty simple idea once you understand how perlite and water interact. Many of the details of the process have been filled in by adventurous netizens who tried the process, modified it, and posted their details to various newsgroups, web boards, or mailing lists. The actual collection of information, writing and layout of the faq were done by Erowid.

Revision History
1.0 - 12/12/97 - Created the basic html FAQ
1.1 - 03/28/98 - Added credit information and health concerns section
1.2 - 04/25/98 - Added info about how long it takes for the perlite to initially humidify the chamber, and a note about the possibility of mason jar lids rusting if they're used to hold the cakes up off the perlite.

1.3 - 01/05/00 - Added Links section 1.4 - 01/11/01 - Made a few minor clarifications
The theory behind the Perlite Humidification Technique is that instead of trying to humidify your growth chamber with a complex humidifier use a layer of perlite to keep the humidity high. In addition to requiring less daily care, some people say the perlite method can sometimes provide up to 4 or 5 flushes. Many people seem to have great luck with this method! If you have any information about using perlite that isn't included here...please let us know.

What is perlite and how does it work?
Perlite is made of small pieces of extremely porous volcanic rock. If you look at is closely (microscopically) you'll see that it looks like swiss cheese with (relatively) huge holes. When water is added, it is wicked into these pores of the perlite. This porous structure then serves to slowly evaporate the water back into the air. The huge surface area in the micropores of the perlite helps the water evaporate forming a vapor of tiny droplets which tend to stay well in the air, as opposed to the bubbler and humidifier methods which have large droplets which tend to condense. This evaporation process takes a while, which is perfect for our purposes, since we want to prolong the evaporating process as long as possible.

Perlite can be purchased from most gardening supply stores. It's generally kept in the same area as bags of dirt, manure, fertilizers etc. A small bag is about $5 and a large bag is about $20. Apparently perlite can also be purchased in automotive stores for use in helping clean up oil to avoid this variety as some sources suggest it is treated with chemicals which may not be good for growing mushrooms.

Health issues with perlite
Inhaling perlite dust is not recommended. Think of it as inahling tiny pieces of glass into your lungs. The problem is, when you buy a bag of perlite, it's often quite dusty. One good solution is to pour a bunch of water, about 10& of the volume of the perlite, into the bag when you first open it. This can significantly help reduce the dust levels. Some bags of perlite even have this suggestion printed on them.

Can I use Vermiculite instead of perlite?
Not recommended. Though some people have used vermiculite successfully, the perlite technique relies on the porous structure of perlite to work. Unlike perlite, Vermiculite actually absorbs water...and creates a big mush in your grow chamber. It's smaller surface area is significantly less efficient at re-releasing the water back into the air.

What do I do with the perlite?
Basically, you're going to cover the bottom of your grow chamber with a layer of wet perlite. The grow chamber should be fairly well sealed and shouldn't have any holes in it. Then, you put your fully colonized cakes in on top of the layer of perlite. The perlite should maintain just about the right level of humidity without any help. Other than daily airing of the grow chamber to reduce CO2 levels, there's very little maintenance with this method.

Is there a problem with contamination of the perlite?
An obvious concern with the perlite technique is sterilization. Intuitively, it just doesn't seem right that one would work so hard to make sure the grow chamber is sterilized correctly, and then dump a big wet pile of unsterilized perlite in the bottom. But generally, there doesn't seem to be much of a problem with contamination of the perlite. Apparently expanded perlite is produced by a process which brings it to 800-900 degrees Celcius, therefore it is certainly sterilized when it goes in the bag. Obviously storing an open bag, especially if it's wet, could introduce contaminants to the perlite, but an unopened bag of perlite should be relatively contaminant-free.

Most people simply use perlite out of the bag, though some swear by boiling or baking the perlite first to sterilize it. It's also possible to add a small amount of liquid sterilizer to reduce contamination.

Hydrogen Peroxide
If you've tried the perlite method and had problems with contamination, or if you'd just like to be extra careful, you might want to try mixing a small amount (.5% solution) of Hydrogen Peroxide into the water. In theory, this low level is enough to help reduce contamination in the perlite layer, but isn't enough to hurt the mycelium since the cakes aren't in direct contact with the liquid. Some people suggest pouring the hydrogen peroxide directly onto the perlite layer before adding the cakes, but I might recommend mixing it directly with the water before adding the water to the perlite so there's no change of the cakes coming directly into contact with any significant amount of the hydrogen peroxide. Either method should work fine.

Though many people recommend using bottled water in order to keep your grow chamber as sterile as possible, others suggest that using tap water adds just enough chlorine into the system to keep unwanted contamination down. You could possibly get the best of both worlds by using bottled water and adding a tiny amount of chlorine bleach to it. This seems to be a matter of personal preference. Whichever works for you.

How much water do I add to the perlite?
There are 2 slightly different methods you can use. The first is to put about 1.5-2 inches of perlite in the bottom of your grow chamber then add about 1/2-3/4 inch of water. The water level needs to be well BELOW the top of the perlite. Only the perlite that is exposed to the air will wick up the water and release it into the air over time. It will take a few hours (depending on the external humidity and size of the chamber) after adding the water to the perlite before the grow chamber will be humidified.

The other method is to put your perlite in a big bowl and add water. You want the perlite to be pretty wet, without having any extra, so fill then pour off the excess. Once the perlite is wet, cover the entire bottom of the grow chamber with a 1.5-2 inch thick layer. With this method, some people like to place thin layers of dry perlite under and on top of the wet perlite layer.

With either method, as the perlite dries, you can occasionally add a bit more water (weekly or so). You should add just enough to keep the perlite wet, but not enough to create any standing water which would increase the chances of contamination. Be careful not to overfill.

Can I put the cakes directly on the perlite?
Your cakes can sit either directly on the perlite layer, or they can be placed on something like upside-down mason jar lids (including the ring). There's no real agreement as to which is best, but there are a few issues to consider when deciding which method to use :

Directly on perlite
It's theorized that some amount of water is fed directly into the cake through absorbtion if the cake is placed directly on the perlite. Some think this may increase contamination, but others say the only noticeable effect is that the mushrooms growing near the base of the cake will often be a bit bulbous and overly wet (sometimes this only happens on the 2nd or 3rd flush), though this is also where some people find the largest mushrooms growing. Cutting the wet mushrooms in half before drying will help with this problem.

On lids
Growing on lids will prevent direct contact between the cakes and the perlite. If you're using hydrogen peroxide and you're worried about the mycelium being hurt, lids may be in order. If the cakes are being grown on lids, you can remove the lids after one or two flushes, or at any point that the cakes seem too dry, in order to get a humidity boost. Others recommend removing the lids for a few days after each flush in order to rehydrate the cakes. The main problem with using metal lids is the posibility that they will rust. Ideally one would use something non-metal.

Just as with most growing methods, the temperature in your grow chamber should be between 70-80 degrees.

Humidity should be as high as you can get it without causing standing water on the cakes. You'd like to be above 95% humidity. If the humidity is too low, you may have problems getting the mycelium to flush, and also may see mycelial growth on the mushroom itself.

CO2 Reminder
Make sure to open your grow chamber and fan it out frequently to disperse excess CO2. Some people do this a couple of times a day and others once every few days.

How long before I can harvest?
After fully-colonized cakes are birthed onto the perlite layer, it will take 1-2 weeks for the cakes to pin and then another week or so until the mushrooms are ready to harvest.

You can keep the same perlite in the grow chamber for as long as the cakes continue flushing. Once your cakes are finished flushing, and before adding new cakes, clean and disinfect the grow chamber and use new perlite.

Other perlite options

Small Perlite Shroomariums (by Bacchus)
If you're using the PFTek formula (rice flour and vermiculite), instead of a using a large humidified aquarium, try making individual shroomariums. Each one is a gallon jar with 1/2" of wet perlite at the bottom. When the cake is ready to be birthed, it is placed in the jar on a plastic lid or something similar.

This method may not yield quite as many or as large shrooms as a fancier, larger, more expensive setup, but it should be more than adaquate for most appetites. This may still benefit from an occasional misting from a spray bottle, but is otherwise pretty maintenence free.


Basic Facts About Perlite - From the Perlite Institute
Porosity Info - Cornell University