8-Pack Organic Sterilized Grain Spawn Bags

Sale Price $127.99 $176.00
SALE

Each spawn bag contains our proprietary blend featuring hydrated, nutrient-rich, organic millet and wheat berries. Bags also include a self-healing injection port for use with a spore or culture syringe plus a 0.2 micron filter patch to block airborne contaminants while providing even gas exchange.

20% Off Sitewide now thru 12/1

Use code: SHROOMSAVINGS at checkout

In Stock. Ships in 1-2 business days.

Why Millet?

Millet has a much lower endospore load than rye and wheat, making it less prone to contamination. And its small size means your spawn will have many more inoculation points for the same volume of grain. By using millet, the mycelium will spread more evenly and abundantly through the substrate. And, as a high-nutrient medium, it also encourages rapid mycelial expansion.

Made Right, Guaranteed
  • Sterilized in a commercial-grade autoclave for consistent results
  • Multiple bags from every batch tested in our state-of-the-art lab
  • Verified using biological indicators and temperature sensors
  • Backed by our 100% Guarantee — if it’s not sterile, we’ll make it right
How to Use

Spawn to bulk ratio

We recommended mixing 1 colonized grain spawn bag with 2-3 bags of sterile substrate. (Higher inoculation rates may improve your success.) 

Best Practices

We recommend clean hands, latex or nitrile gloves, and sterile technique when using sterile substrate to reduce the introduction of contaminants.

Be sure to mix colonized grain spawn thoroughly into your substrate. 

It is best practice to wait a minimum of 1 week after arrival before using sterile substrates to ensure they were not compromised during transit. Rest assured that your purchase is 100% guaranteed. If your substrate was compromised, we will replace it.

Storage

Sterile substrates should be stored at room temperature out of direct sunlight. No refrigeration is necessary. They can also be stored for several months before use.

Notice

North Spore's products shall be used only for lawful purposes. North Spore does not condone Psilocybin (Psilocybe cubensis) or hallucinogenic (magic) mushroom growing in jurisdictions where it is currently illegal.

CA Prop 65 Notice

Grow Right
"Boomr Bin" Monotub
"Boomr Bin" Monotub (+$24.99)

The best grow chamber for bulk substrate

NocBox Still Air Box
NocBox Still Air Box (+$74.99)

Reduce contaminants when you mix or inject substrate

Syringe Multiplier & LC Kit
Syringe Multiplier & LC Kit (+$29.99)

Multiply any spore or syringe into 30 syringes!

8-Pack Boomr Bag
8-Pack Boomr Bag (+$127.99)
Nitrile Gloves
Nitrile Gloves (+$13.99)

Stay clean, stay sterile

Sterile Substrate FAQs

Choose Boomr Bag for massive flushes of dung-loving species, CVG for versatile bulk grows and great moisture retention (great for beginners), and Wood-Lovr for wood-loving species like oysters, lion’s mane, and reishi. Each is optimized for the best yield and growth rate in its category.

Keep bags at room temperature and out of direct sunlight. Substrates can be stored for several months, and grain bags should be used within a few weeks for best results.

We sterilize our products in commercial autoclaves and test every single batch for bacterial growth so you know the product is sterile when you receive it. And if the bag is compromised in any way during shipping, our 100% guarantee means we'll make it right

While you can grow directly in the bag, the best way to grow with bulk substrate is to to use a monotub.

A general rule is 1 colonized grain bag for every 2–3 substrate bags. Higher spawn ratios often speed up colonization and reduce the risk of contamination.

Grain bags are for colonizing mycelium, while sterile substrates (like Boomr Bag, CVG, or Wood-Lovr) are for fruiting mushrooms. You’ll inoculate the grain bag first, then mix the fully colonized grain with your chosen substrate to begin fruiting.

Cluster of brown-capped mushrooms with long, light-colored stems against a white background.

Lab-Crafted. Grower-Approved.

Get the most out of your grow with our premium sterilized substrates—formulated, hydrated, and sterilized to deliver consistent, high-yield results. Each batch is crafted from organic ingredients and sterilized in a commercial-grade autoclave for contam-free performance. Whether you’re spawning to bulk for the first time or fine-tuning advanced grows, our substrates provide the perfect foundation for strong, healthy mycelial growth.

The right mix for every grow

Our substrates start with premium organic ingredients—nutrient-rich, finely milled, and perfectly balanced for ideal texture, aeration, and moisture. Each blend is designed by mycologists to support vigorous mycelial growth and consistent, high-yield harvests. Built on quality ingredients and precise formulation, they’re the foundation every successful grow begins with.

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