Mushroom Fruiting Blocks: Growing Guide for Beginners

Mushroom Fruiting Blocks: Growing Guide for Beginners

Updated on 10/25/25

You've just picked up your first mushroom fruiting block—now what? Whether you're after fresh Lion's Mane for cooking or the satisfaction of cultivating your own food, growing mushrooms at home is a deeply rewarding hobby. This guide is your step-by-step walkthrough for getting the most out of your block: from sterilization and inoculation to fruiting and harvest.

Choosing the Right Mushroom Species

Dried MushroomsBefore anything else, pick a species that suits your experience level and growing space:

 

  • Best for Beginners: Oyster mushrooms and Lion's Mane grow quickly and tolerate a variety of substrates.
  • Flavorful Favorites: Shiitake offers deep umami and is perfect for home cooks.
  • Avoid Indoors: Wild species like morels are tricky and better suited to outdoor environments.

Consider your home environment (temp, humidity, airflow) and how hands-on you want the process to be.

Preparing the Substrate

Your substrate is the fuel your mycelium will feed on. There are many ways to make it, but our go-to recipe for a 5 lb fruiting block is:

  • 5 cups hardwood pellets
  • 1,400 ml water
  • 1.25 cups wheat bran
  • Optional: Gypsum for extra shroom food

Common materials include hardwood sawdust, straw, coffee grounds, and coco coir. Nutritional supplements like wheat bran, vermiculite, or gypsum can speed growth and improve yields.

Sterilization is key. Use a pressure cooker at 15 PSI for 2 hours. Sawdust insulates well and requires thorough sterilization to avoid contamination.

A Presto Pressure Cooker and impulse sealer work great at home. I’ve consistently hit 95% success using this combo.

Inoculating the Block: The "Spawn Run"

Mycelium Advance

Once your substrate is sterilized and cooled, it's time to inoculate with mushroom spawn. Rye grain spawn is a common choice and easy to find.

Tips for success:

  • Work in a clean area; use gloves and sanitize surfaces.
  • Fold or loosely seal bags during sterilization to minimize exposure.
  • After adding spawn, reseal the bag and shake gently to distribute.

Now comes the spawn run: the incubation phase where mycelium colonizes the substrate. This usually takes 2–4 weeks depending on temperature and species.

I use the coolest closet in my house to keep things around 65–70°F. Massage the block gently halfway through to trigger additional growth.

Fruiting Conditions: From Block to Mushrooms

Once fully colonized (the block turns white and dense), it’s time to fruit. Here’s how to transition to a fruiting environment:

Ideal fruiting conditions:

  • Temperature: 60–70°F
  • Humidity: 85–95%
  • Light: Indirect or diffused light

How to Initiate Fruiting:

  1. Clean outside of bag with isopropyl alcohol.
  2. Cut 2–3 small X-shaped slits with a sterile blade.
  3. Lightly mist those areas just once.
  4. Place in fruiting chamber and monitor daily.

A simple DIY fruiting chamber:

  • Use a clear plastic tote with 1" holes drilled on all sides.
  • Mist the walls, not the cuts, to keep humidity high.
  • Here's a guide from Reddit to help

Harvesting & Post-Flush Maintenance

Lady Smelling Fresh Mushrooms

Each variety has its visual cues:

  • Oyster mushrooms: Harvest when caps flatten.
  • Lion's Mane: Harvest when spines elongate.

Use a twist-and-pull motion or cut at the base with a clean knife.

After harvest:

  • Mist the block to rehydrate.
  • Return to fruiting chamber.
  • Watch for a second flush in 1–2 weeks.

Once your block stops producing (usually after 2–3 flushes), repurpose it! Spent blocks make excellent compost or garden additives.

Troubleshooting Common Issues

Contamination is the biggest risk, thankfully we wrote an extensive blog on how to overcome almost any issue when growing mushrooms! [Mushroom Grow Bag Not Fruiting]

Look for:

  • Odd smells
  • Green/blue/black fuzzy patches
  • Rapidly spreading spots unlike the rest of the mycelium

Prevention tips:

  • Always sterilize properly (don’t split sessions).
  • Keep bags sealed until fully colonized.
  • Clean your fruiting chamber weekly with peroxide or alcohol.

If in doubt, let the bag grow for a few more days. Mycelium is often confused with mold at early stages.

Final Thoughts

Growing mushrooms at home is part science experiment, part meditation. With clean technique and a little patience, your fruiting block can provide multiple harvests of gourmet mushrooms.

Whether you’re just starting or refining your grow process, remember: contamination is part of the learning curve. Stick with it, keep things clean, and enjoy the process.

Additional Resources: