How to Build a Home Fruiting Chamber

Select and build the right fruiting chamber to start your own home mushroom cultivation project using one of these chamber methods.

Photo by Getty Images/dangphoto2517

Fruiting in Vessel

Simply fill vessels partway with substrate, leaving closed-off air space at the top. The humidity of the substrate usually provides enough for fruiting. This doesn’t work for all species, but reishi, pioppino, lion’s mane, enoki, and others with high CO2 tolerance can fruit like this. Others will either refuse to fruit or will form tough, exaggerated stems.

Humidity Tent

A humidity tent is the easiest and cheapest option, but it has a small capacity and doesn’t allow any automation. It is simply a light frame or rack larger than the vessel to be fruited with a plastic bag over it. It can be hung or placed on a surface. It can have a moisture-holding medium in the bottom such as perlite, coir, peat, or a folded towel to evaporate moisture into the chamber. Mist the inside walls of the tent 1–5 times per day. Make sure there are holes or slits at top and bottom to allow airflow and drainage. The heavier CO2 will fall out the bottom and be passively replaced by fresh air through the top. Having multiple tents can allow blocks of different species and ages to each have their own microclimate, and to segregate contaminated kits that are fruiting anyway.

Shotgun Fruiting Chamber (SGFC)

Invented by Marc R. Keith/RogerRabbit and widely used as a small fruiting chamber, the NPQ? uses natural air currents to provide high RS and QTU. Moistened and drained perlite fills the bottom and provides constant evaporative humidity and airflow. As humid air is less dense than dry air, the evaporation causes an updraft and further evaporation as fresh air is pulled in from the holes in the bottom. Supplemental misting is usually necessary, and if mushrooms show signs of CO2 overload, fanning out stale air with the lid occasionally helps.

A local oyster strain fruits from coffee grounds in a fully automated, mono-tub-like terrarium. The timer runs a small computer fan intake, and a humidstat activates a pond fogger in-line after the intake. The plant sits atop a vacuum cleaner HEPA filter repurposed as an exhaust filter to prevent contaminating the human living space with sports.
Photo by Charlie Aller
  1. Get a large (+/– 64qt [61 L]), clear-plastic tub with a lid and a bag of perlite (available at garden stores).
  2. Drill 1/4" holes in a 2" (5 cm) grid on all sides, including lid and bottom.
  3. In a large colander, thoroughly rinse and drain perlite in batches, filling tub until 4–5" deep.
  4. Situate tub on a table or shelf, not on the floor (to avoid contaminants).
  5. Elevate tub at least 2" (5 cm) off its resting surface with blocks and keep sides of tub at least 2" (5 cm) from any walls to allow airflow.
  6. Place fruiting blocks or jars within, allowing ample space for mushroom development.
  7. Mist 1–3 times per day, or as needed.
  8. If mushrooms are too stemmy, increase QTU by fanning or place a fan in the room blowing near but not directly on the tub.


Another contribution from the online mushroom community, this system was designed for compost-loving mushrooms, but it can also work for reishi, king oyster, and others that are willing to top-fruit. The optional lining is to prevent primordia from forming on the sides. Pasteurized substrate and spawn are mixed, incubated, and fruited in the tub. Maintenance is minimal if set up properly. Many sizes and designs exist; here is how to make one time-tested model:

  1. Get a large (+/– 64qt), clear-plastic tub with a lid, some 2" tape (non-porous), a trash bag or plastic sheet (optional), and some polyfill.
  2. With a 1-1/2" (38 mm) hole saw, drill two evenly spaced holes 5" (13 cm) up from the bottom of the tub on each of the long sides. Drill two more 1-1/2” (38 mm) holes just under each of the handles on the short sides. When drilling, use light pressure so you don’t crack the tub.
  3.  Invert tub and wrap the bottom like a gift, taping folds into place. If you wish, you could slip off the wrapping and put it inside tub as a liner, taping the top edge of the plastic to the tub.
  4. Fill with hydrated and pasteurized substrate and spawn (ratio depends on mushroom species and substrate) to 1" (2.5 cm) below the lower holes, or less if you plan on casing. Mix thoroughly and level, but do not pack.
  5. Using scissors, cut away excess plastic liner (if using) at substrate level, or above if casing later.
  6. Put the lid on the tub and cover the six holes with tape. The lid isn’t airtight and allows for enough gas exchange. Incubate.
  7. If applying a casing, do so as soon as substrate is fully myceliated, and incubate again.
  8. When fully myceliated, initiate fruiting by removing the tape and replacing with a wad of polyfill in each hole. Stuff top holes loosely and lower holes tightly. Adjust polyfill density to dial in RS:QTU balance. Mist and or fan with lid only if necessary. Monotubs can be fruited indoors, or outdoors if temperatures are fairly consistent and agreeable.
  9. Substrate block can be taken out of tub to facilitate harvest. Replace substrate block, briefly soak, and drain for subsequent flushes.

The Shower

Pink oysters cozy up beside bath toys at our house.
Photo by Willoughby Arevalo

The bathroom is usually the most humid room in the house, though kitchens often get quite steamy. Hang bags in the shower but outside of the direct spray and shampoo splash zone (mushrooms don’t need shampoo, possibly with the exception of lion’s mane). A few showers per day may provide surcient humidity to support fruitings of oysters and others that don’t need consistently super-high humidity. If showering alone doesn’t provide enough humidity, you can always mist by hand too. A spare shower stall is easily converted to a dedicated fruiting chamber with the addition of racks and a humidifier.


A mini-greenhouse set up with two cool mist humidifiers, outdoors at Wildwood Ecology Labs.
Photo by Theo Rosenfeld

Basically, this setup is a big humidity tent over a rack, automated with humidifiers, lights, and fans. It can be situated indoors or in a shady outdoor location, temperatures permitting. In the online forums, this unit is called a Martha, because the first ones were made from Kmart Martha Stewart storage closets retrofitted with racks.

Subscribe Today - Pay Now & Save 64% Off the Cover Price

50 Years of Money-Saving Tips!

Mother Earth NewsAt MOTHER EARTH NEWS for 50 years and counting, we are dedicated to conserving our planet's natural resources while helping you conserve your financial resources. You'll find tips for slashing heating bills, growing fresh, natural produce at home, and more. That's why we want you to save money and trees by subscribing through our earth-friendly automatic renewal savings plan. By paying with a credit card, you save an additional $5 and get 6 issues of MOTHER EARTH NEWS for only $12.95 (USA only).

You may also use the Bill Me option and pay $17.95 for 6 issues.

Canadian Subscribers - Click Here
International Subscribers - Click Here
Canadian subscriptions: 1 year (includes postage & GST).

Facebook Pinterest Instagram YouTube Twitter flipboard

Free Product Information Classifieds Newsletters