Fruiting Chambers: How to Select, Build, and Operate the Ideal Chamber for Your Needs

Selecting the proper fruiting chamber for your needs sets the stage for your effectiveness as a cultivator.  The ideal fruiting chamber for you depends on what species of mushroom you're working with, the amount of time you can devote to care and maintenance, and the amount of space you have to work with.  Following is a description of the various fruiting chambers and their advantages and disadvantages for use, as well as instructions for their construction and operation.  You do not want to place a fruiting chamber on the floor during fruiting as most contaminate spores will settle in the 2 feet of air above the floor.

Shotgun Fruiting Chamber:  Recommended for new growers who are working with PF Tek cakes.  This chamber needs to be elevated so that air can pass underneath it, and must be used in a room without air flow.  This chamber operates by using the small amount of heat generated by the living mycelium to pull humid air up through the bottom of the chamber as the warmer air rises.  This chamber requires regular, daily maintenance, but can be left alone for up to 14 hours at a time.  Must be lit externally.


The shotgun fruiting chamber is built from a clear plastic tub (12 inches tall is ideal) that you have drilled 1/4" holes 2 inches apart in a grid pattern on all six sides (yes that includes the top and bottom).  You then fill the bottom 5 inches of the tub with damp perlite (a little will fall out while loading, but not much).  When placing cakes into the shotgun fruiting chamber, place them on squares of foil so that they don't come into direct contact with the perlite.  Prop the chamber up on blocks so that air can pass under it.  The perlite can be reused between grows, simply rinse it out and place it back into the chamber.  If you dealt with contaminates within the chamber on the previous grow, you can spread the perlite out on a cookie sheet and heat the perlite in the oven for a hour at 450 to sterilize it.

The shotgun fruiting chamber needs to be fanned (take the lid off and wave a paper plate at the cakes for about 5 seconds) at least twice daily to help keep CO2 from building up.  For species like oysters that need a lot of fresh air exchange, it is recommended to leave the lid off entirely.  Cakes in a shotgun fruiting chamber should be misted (sprayed with a water bottle) twice daily before being fanned.  See the species page for specific cultivation instructions regarding your mushroom of choice.

Monotub:  A low cost, low maintenance bulk fruiting chamber.  This chamber is a great first step into bulk cultivation, but is not ideal for all species of mushroom.  This chamber will benefit from a fan being on in the same room, but not pointed directly at it.  The best location for this fruiting chamber is on a desk or table.  Must be lit externally.


The monotub is a great bulk method of set and forget cultivation.  To construct a monotub, you will need to find a clear plastic bin that you feel is a manageable size for you to work with.  You then drill 2 2" diameter holes on each of the long sides, ensuring that the bottom of the hole is 4" up from the bottom.  You also drill 1 2" hole near the top of the tub on each of the short sides.  Cover the bottom 4 inches with black electrical tape to help prevent side and bottom pinning of the substrate.  Particularly large tubs may require additional holes.

There is some math involved with figuring out how much spawn and substrate you will need to properly fill the monotub to substrate level.  The equation to remember is simple: Lenth x Width x 4 = Substrate Volume in cubic inches.  You need to convert this into quarts with the equation Sustrate Volume / 57.75 = Quarts

For example:  We have a tub that is 24" long, and 12" wide.

24 x 12 x 4 = 1152 / 57.75 = 19.9 Quarts

So for this monotub, we'll need 20 quarts of spawn and substrate.

When spawning to a bulk substrate, you want to use a 1:3 spawn ratio.  This means that for every 3 quarts of substrate, you will need 1 quart of spawn.  For the tub in the example, we would want 5 quarts of spawn, and 15 quarts of substrate.

When you mix your spawn and substrate together to put into the monotub, save a little substrate to cover any exposed spawn grains with, so that when you look down into the tub, you only see substrate.  You will need to cover the holes with duck tape during colonization.  Once the tub is fully colonized, remove the duck tape, and put polyfil in each of the holes and switch from ambient lighting to a direct lighting cycle.  The polyfil will allow for fresh air exchange while keeping humidity inside the monotub.  Misting and fanning should not be necessary unless the polyfil is too lose or too tight.  Mushrooms with fuzzy bases at the bottom of the stipe, or continued colonization without fruit production are indications that the polyfil should be loosened.  The substrate turning blue is an indication that the polyfil is too lose, and that the substrate is becoming stressed from drying out.

After a flush has been harvested, pour a gallon of water into the tub to help rehydrate the substrate.  After 12 hours, pour out any unabsorbed water and put the monotub back into fruiting conditions.

Greenhouse:  My personal favorite fruiting chamber.  Greenhouses can be cheap or expensive to set up depending on if you get a pre made unit, or build your own.  Most of the cost is in the hardware used to control the conditions inside the greenhouse.  Getting the timers or sensors set properly can be tricky, and wreak havoc in overly complicated setups when something is out of tune.  A perfectly dialed in greenhouse can easily maintain a no maintenance environment that constantly supplies your mushrooms with their beloved fresh air and humidity.  May be lit externally or internally.  Lights used inside a greenhouse must be waterproof to survive operation in a high humidity environment.

1 comment: