Growing Mushrooms using Grain Spawn

Growing Mushrooms using Grain Spawn

Growing Mushrooms using Grain Spawn: A Beginners Guide

Growing your own mushrooms is one of the most rewarding DIY food projects you can take on. With just a little preparation and the right materials, you can turn a few bags of grain spawn into a steady supply of fresh, gourmet mushrooms. Whether you’re interested in oyster mushrooms for quick harvests or shiitake for rich, savoury flavour’s..Grain spawn is where the process of growing mushrooms starts for most!

Below, you’ll learn what grain spawn is, why it’s useful, and how to grow mushrooms with it from start to finish.

What Is Grain Spawn?

Grain spawn is simply mushroom mycelium grown on sterilised grains (like rye, millet, or wheat berries). The mycelium uses the grain as a nutrient-rich platform from which it will later colonise a bulk substrate. Sam refers to grain spawn as mushroom baby food!

Think of it like a starter culture, like sourdough starter, but for fungi.

Why use grain spawn?

Fast colonisation: Mycelium spreads quickly through small grains.

Even distribution: You can mix spawn evenly into bulk substrate for consistent growth.

High success rate: It reduces contamination risk compared to colonising from liquid culture.

What You’ll Need

Grain spawn (purchased from us)

Bulk substrate
Examples:

Pasteurised straw (great for oyster mushrooms)

Hardwood sawdust + bran (great for shiitake or lion’s mane)

Coir/vermiculite blends (great for the jazzy ones)

Growing container
Options:

Filter patch grow bags

Plastic totes with holes

Buckets with lid and side fruiting holes

How To - Growing Mushrooms with Grain Spawn

1. Prepare Your Bulk Substrate

The substrate is the material that the mycelium will colonise and eventually fruit from.

Straw: Chop into small pieces and pasteurise by soaking in hot water (~65–70°C/150–160°F) for about an hour.

Coir/vermiculite: Hydrate with boiling water (as done in many in many YouTube videos).

Hardwood sawdust: Can be bought as pellets or often purchased as pre-sterilised blocks.

The substrate should be Field Capacity, not dripping but not too dry. 

2. Mix Grain Spawn into Your Substrate

Once the substrate has cooled:

  1. Clean your hands and workspace to reduce contamination.

  2. Break up the grain spawn so the grains separate.

  3. Mix spawn evenly into the substrate.
    A common spawn ratio is 10-12% of the fruiting substrate.

Even mixing ensures fast, healthy colonisation.

3. Incubate the Mixture (Colonisation Stage)

Place the inoculated substrate into your chosen container:

Fruiting bags: Seal or fold them.

Buckets/totes: Close the lid or cover with breathable material.

Ideal conditions:

Temperature: 20–24°C (68–75°F) for most gourmet species

Light: Not required at this stage

Airflow: Minimal—mycelium prefers a still environment during colonisation

Within 10–21 days, depending on species and temperature, the substrate will turn fully white as mycelium spreads.

4. Introduce Fruiting Conditions

Once fully colonised, your block needs to “wake up” for fruiting.

Fresh air, humidity, and gentle light trigger mushrooms to start ‘pinning’

Create fruiting conditions by:

  • Cutting a slit in the fruiting bag

  • Uncovering holes on buckets

  • Placing the block in a fruiting chamber or well-ventilated area

  • Misting walls/air around the block daily

  • Keeping humidity high (70–90%)

  • Providing indirect light (a bright room is enough)

Tiny mushroom pins will appear within days. (Usually)

5. Harvest Your Mushrooms

Once the mushrooms have:

  • Formed full caps

  • Shown their mature shape

  • Reached desired size

…gently twist and pull them from the block. Most species fruit in flushes, so you can expect 2–3 harvest rounds from a single block.

Tips for Best Results

  • Choose beginner-friendly mushrooms: Oyster and lion’s mane are ideal for new growers.

  • Keep it clean: Contamination usually comes from dirty tools or unpasteurised substrate.

  • Don’t overwater: Mist the environment -Not the mushrooms directly!

  • Use fresh, vigorous spawn: Grain spawn has a shelf life.

Why Grow Mushrooms at Home?

  • Fresh mushrooms taste significantly better than store-bought.

  • It’s an eco-friendly hobby that can potentially be grown from waste.

  • You can produce large yields for low cost.

  • Watching mycelium grow is surprisingly satisfying!

Growing mushrooms using grain spawn is one of the simplest, most reliable methods for home cultivators. With a bit of preparation and attentive care, you can enjoy continuous harvests of gourmet mushrooms right from your own home :)

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