Growing Shiitake Mushrooms Indoors at Home: A Simple, Step-by-Step Guide

When you lack outdoor space, growing your own food can seem impossible. But if you choose the right produce, you don’t need soil or sunlight.

Growing shiitake mushrooms indoors is an easy alternative to the traditional home garden. With just a bag of sawdust and a dark room, you can begin reducing your grocery bill and carbon footprint without ever going outside!

What You Need:

• 5 cups of hardwood sawdust pellets or fresh sawdust
• 5/8 pounds shiitake mushroom grain or sawdust spawn
• 1 ¼ cups wheat bran
• 5 lb grow bag with filter patch
• Cloth or paper filters
• Large tub
• Water
• Rubber gloves
• Pressure cooker (optional)
• Heat-proof gusseted plastic bags (optional)
• Jar lids (optional)

Picking Sawdust Pellets:  Shiitake mushrooms naturally grow best on oak substrate (the word “shiitake” means mushroom of the oak). If oak sawdust is not readily available, you can use other deciduous hardwoods like beech, ironwood, or maple (1).

How To Grow Shiitake Mushrooms Indoors

1. Pasteurize the Substrate

Substrate needs to be pasteurized (exposed to high temperatures) before it is inoculated with mushroom spawn. Pasteurizing eliminates any microorganisms like fungi or bacteria that could kill or otherwise harm your shiitake mushrooms. This step is key for keeping mold from growing in what would otherwise be its ideal breeding environment (a cold, dark, damp bag).

The method by which you prepare your substrate will depend on the substrate itself. If you’re using sawdust pellets, they’ve already been pasteurized and simply need to soak in 1.4 liters of water for 30 minutes to break down the pellets into usable sawdust. If you’re using regular sawdust, you can pasteurize it by filling a large tub with hot water (149 – 176 degrees F or 65 – 80 degrees C) and soaking the sawdust for 1 to 2 hours.

2. Sterilize The Substrate

Some shiitake growers suggest sterilizing your substrate in addition to pasteurizing (2). While this is not always necessary or possible, if you are able to sterilize your sawdust it can only improve your shiitake mushroom growing conditions.

To sterilize your substrate, fill a heat-proof plastic bag or bags with pasteurized sawdust. Place a filter in between the gussets to prevent contamination while the sawdust cools, then fold down the gussets. Easy filters can be made from Tyvek or scraps from a painting suit (3).

Place jar lids on the bottom of the pressure cooker to elevate the bags, and then stack bags on top to fill. Fill the cooker with water just until it reaches the top of the bottom bag, then place something heavy (a plate will work) on top of the top bag to prevent it from clogging the relief valve. If you don’t weigh down the top of the bag, you run the risk of dangerous levels of pressure building up inside the cooker.

Heat the substrate at 250 degrees Fahrenheit (120 degrees Celsius) for 2 ½ hours, then allow it to cool for at least 8 hours. The substrate temperature must be below 86 degrees Fahrenheit (30 degrees Celsius) or it may kill your shiitake spawn before it’s able to grow.

3. Inoculate Your Grow Bags

The process of introducing mushroom spawn to a substrate is called inoculation. Inoculation needs to happen in a clean area, so wipe down any surfaces you will be using, including a large plastic tub, with a disinfectant. Wearing disposable rubber gloves is also recommended. Before you begin, check the water content of your pasteurized or sterilized substrate. When you squeeze the sawdust, a few drops of water should come out, but not more.

In the clean plastic tub, gently mix the substrate, wheat bran, and grain or sawdust spawn. Once incorporated, transfer the sawdust spawn mixture to your grow bag and close it with tape, a rubber, band, or a zip tie. 

Pro-Tip: Substrate, grain, spawn, and grow bags can be purchased all at once from mushroom-growing supply companies like NorthSpore.com

4. Incubate the Shiitake Spawn

When gardening inside, the right location is everything. Luckily, shiitake mushrooms need just a few things while they’re incubating: nutrition, and a dark, humid environment. 

The recipe provided will yield one 5lb bag, which is about 5 inches wide by 8 inches deep, and around 18 inches tall. Find a space off the ground that is slightly larger than your bag. The space shouldn’t receive much sunlight, but it should maintain a relatively high level of humidity (somewhere around 65%). You can supplement the humidity of a closet or dark room with a humidifier, or keep the bag in a naturally humid area like a bathroom or basement. Shiitakes also do best in a cold or room-temperature climate, so keep the bags away from warm areas like kitchens and attics.

The first signs of growth will come after 2 to 3 months in the form of thin, white mycelium. These may look like little white hairs. When the sawdust block is completely colonized and bumps have formed, you can make some slits in the bag to increase aeration and promote browning.

Unlike other mushrooms, shiitake is not ready to fruit when the mycelium is white. Shiitakes consolidate their growing mycelium, leading to large blobs and brown patches. It may look like the block is rotting, but it means your shiitakes are getting ready to fruit. When the mycelium is mostly brown and has formed large knots (this will take about two more weeks) you can begin the fruiting process.

5. Induce Fruiting

Mushrooms do not sprout on their own, rather, your shiitake mushrooms will need to be shocked into bearing fruit. Shocking imitates the natural environmental changes that a shiitake mushroom would experience when growing outdoors. A physical strike mimics a tree falling, while a cold shock tells the spawn that winter is coming and the time for fruiting is now. 

To cold shock the incubated block, pick a location that is consistently between 37 degrees Fahrenheit (3 degrees Celsius) and 41 degrees Fahrenheit (5 degrees Celsius). This can be outdoors in the winter, in a large cooler, or inside your refrigerator. The key to cold shocking is to have the spawn experience a dramatic change in temperature, so the exact location is less important than the difference in climate. Once you have selected a location for the cold shock, keep the bag there for 24 to 48 hours.

You can also smack the bag of shiitake mushroom spawn with your hand on all sides before moving it into a cold shock (4).

After shocking the shiitakes, remove the substrate block from the bag and place it in a humid area with plenty of air flow. Mist the block with water several times a day, and after about a week, your block should begin fruiting.

6. Harvest Your Shiitake Mushrooms

Once your block begins growing shiitake mushrooms, you can harvest them at any time before their caps flatten. If the caps of the shiitakes begin to flatten out and release spores, they’re no longer good for eating. If you want more tender mushrooms that last longer, harvest the shiitakes while they are still small. For a more exact harvesting schedule, Fresh Cap Mushrooms says “commercial growers usually harvest the fruits right before the caps start to uncurl from the stem.”

To harvest your mushrooms, use a sharp, clean knife to cut the shiitake at the base of its stem. Using your hands to twist the shiitake mushroom off the block can damage the Mycelium and harm future mushroom growth.

Pro-Tip: You can increase the Vitamin-D content of your harvested mushrooms by placing them in the sun (gills up) for 24 to 48 hours after removing them from the spawn block.

7. Recover Your Spawn Block

Every sawdust spawn block can produce 3 to 5 flushes of shiitake mushrooms in its lifetime before the mycelium becomes too weak to fruit. To promote new growth after harvest, move the block to an area at about 70% humidity that can be kept between 68 degrees Fahrenheit (20 degrees Celsius) and 86 degrees Fahrenheit (30 degrees Celsius). 

Let the block rest for 1 to 3 weeks and then restart the fruiting process at the shocking stage. You can repeat this process of recovering and fruiting until your yields decrease and mold begins to grow on the sawdust spawn block. When the block has produced its last fruit, the whole thing can be composted, and nourish a new generation of produce.

Have you read our step-by-step guide on how to grow shiitake mushrooms on logs yet?

If you’re looking for an even more beginner-friendly and no-tools-required way to grow mushrooms, check our best mushroom growing kit reviews.