How much spore solution or liquid culture should I inject into a spawn bag?

We recommend about 5cc total per spawn bag, distributed across several injection points. A little more or less can still work, but overdoing it adds excess moisture.

What is the ideal temperature for incubating spawn bags?

The ideal incubation range is 72–76°F. Bags generate 3–4°F of internal heat while colonizing, so avoid ambient temperatures above 78°F to prevent condensation and wet spots.

What if my spawn bag seems stalled at 75% colonization?

Mark the current growth line with a marker and check again after a week. If the mycelium has not advanced, you can remove the cake, brush away any uncolonized grain, and use only the fully colonized portion in your bulk substrate.

What's the difference between using a spawn bag and a grain jar?

Spawn bags hold more grain (typically 3–5 lbs) and use a self-healing injection port plus a filter patch for gas exchange. Grain jars are smaller (typically quart-sized), use 3–5cc of solution each, and require the foil cover to be removed after sterilization. Both produce the same end result — fully colonized grain spawn for bulk growing.

Growing 101 · Spawn Guide

Spawn Bag & Grain Jar Guide

Q: Does light matter during spawn bag colonization?

Most growers traditionally incubate spawn in the dark, but current experience shows light usually does not have a major effect on colonization. Use whatever setup is most convenient and stable for your environment.

How to inoculate, incubate, break up, and fully colonize sterilized spawn bags and 5-grain jars — start to bulk-ready in about 4 weeks.

Our pressure-sterilized grain bags and jars are designed to arrive fresh and ready to use. This guide walks you through the full process from first injection to fully colonized grain ready for bulk substrate.

Shop Spawn Bags Shop Grain Jars Download PDF

By Midwest Grow Kits Team Updated: May 2026 Read time: 8 minutes Difficulty: Beginner-friendly

Incubation Temp

72–76°FIdeal range

Inoculation Amount

~5ccPer spawn bag

Time to Colonize

3–4 weeksBag to bulk-ready

Break & Shake

Day 12–18At 20–30% colonized

On This Page

Before You Start Video Walkthrough Inoculating Incubating Break & Shake Bags vs Jars Tips & FAQ After 100% Colonized 5-Grain & Rye Jars Need Help?

Things to Know Before You Start

A quick checklist of fundamentals before your first injection. The single most important factor in mushroom cultivation success is sterile technique.

Freshness & Storage

We ship our spawn bags and grain jars the day after they are made so they arrive fresh and ready to use. For best results, use them within 4–6 weeks of receiving them.

Store your bags or jars in a cool, dark place and leave them inside the protective outer bag until you are ready to inoculate.

Before use, visually inspect the bag or jar for any obvious signs of contamination such as green, white, or grey mold. Some grains such as milo and rye may appear dark or dry on the outside due to their natural outer hull — this is normal.

Anatomy of a Spawn Bag

Each spawn bag includes a black self-healing injection port and a white filter patch. Inject your spores or liquid culture through the black port. The white filter patch allows clean gas exchange while helping keep contaminants out.

Avoid touching the white filter patch whenever possible, since oils from your skin can affect it.

The most important step in this process is using proper sterile technique. Clean your work area, turn off fans or moving air, use a new needle, wipe the injection port with alcohol, and work quickly.

Important things to know before inoculating sterilized grain spawn bags

Watch the Full Walkthrough

Prefer to watch it done? This video covers the exact process described in this guide, from sterile prep through inoculation and incubation.

Step 1 of 3

1Inoculating the Bags

Start by preparing the bag and syringe in a clean workspace. A still air box or laminar flow hood is strongly recommended whenever possible.

Remove the top layer of heat tape by locating the flap and slowly peeling it away. Do not remove the tape that covers the black self-healing injection port.
Remove a new sterile syringe needle from its packaging and attach it securely to the syringe.
Wipe the black self-healing injection port with an alcohol wipe for 15–20 seconds.
Shake the syringe well, remove the needle cap, and insert the needle through the black port.
Push the needle about 1 inch into the bag, angle it upward, and slowly distribute the solution into different areas of the grain. Spreading the spores or culture around helps speed colonization.

Recommended Injection Amount

We recommend injecting about 5cc total per spawn bag. A little more or less can still work, but overdoing it can add excess moisture.

Removing outer heat tape from a sterilized grain spawn bag

Remove Tape

Attaching a sterile syringe needle before inoculating a grain spawn bag

Connect Needle

Wiping the self-healing injection port with alcohol before inoculation

Wipe Port

Injecting spores or liquid culture into a grain spawn bag

Inject Spores or Culture

Step 2 of 3

2Incubating

Place your spawn bags in a warm, dark location to incubate. The ideal temperature range is 72–76°F.

Unlike jars, spawn bags often colonize from the inside out, so you may not see visible mycelium growth for 7–14 days.

About 6–7 days after inoculation, unroll the top of the bag and allow a small amount of air to enter through the white filter patch. An easy way to do this is to hold the top of the bag for a few minutes and let gravity slowly inflate it.

Spawn bags generate some internal heat while colonizing, so the inside of the bag is often 3–4 degrees warmer than the room around it. Try to avoid incubating above 78°F, since higher temperatures can lead to extra condensation and wet spots that slow growth.

When working with larger quantities of bags, using liquid culture or agar can help you skip the germination step and improve consistency.

Unrolled mushroom spawn bag during incubation allowing filtered airflow

Bag Unrolled for Gas Exchange

Early mushroom spawn bag colonization around day 10 after inoculation

Early Colonization Around Day 10

Step 3 of 3 · Optional

3Break & Shake

Once your spawn bag is around 20–30% colonized, usually around 12–18 days, you can optionally break up and redistribute the mycelium to speed up overall colonization.

Start by gently breaking up the visible white mycelium into smaller pieces. Then mix the colonized grain through the rest of the bag by shaking and kneading it.

After mixing, carefully reform the bag and repack the grain so there are no large air gaps. Lightly dropping the bag from a short height onto a counter can help settle the grain back into shape.

Return the bag to incubation and leave it undisturbed. You may not see changes immediately, but within 5–8 days you should start to see new growth throughout the bag.

Breaking up partially colonized grain spawn bag to speed colonization

Break & Shake at 20–30% Colonization

Spawn bag seven days after break and shake showing recolonization

7 Days After Break Up

Spawn Bags vs Grain Jars

Both produce the same end result — fully colonized grain spawn — but each has its own strengths. Here's how they compare.

Spawn Bags

5-Grain & Rye Jars

Typical Size

3–5 lbs of grain

Quart-sized (~1 lb)

Inoculation Amount

~5cc per bag

3–5cc per jar

Gas Exchange

White filter patch

Filter lid (remove foil after sterilization)

Best For

Larger bulk grows, monotubs

Smaller batches, beginners, visual monitoring

Colonization Time

3–4 weeks

2–3 weeks

Break & Shake

Easy — flexible bag

Shake jar gently at 30% colonized

Spawn Bag Tips & Frequently Asked Questions

The questions our customer support team hears most often. Tap any question to expand the answer.

Does light matter during colonization?

Most growers have traditionally incubated spawn in the dark, but current experience shows light usually does not have a major effect on colonization. Use whatever setup is most convenient and stable for your environment.

Can I use a heating mat?

Yes, but keep the bag at least 1 inch above the mat. Heating mats can develop hot spots that dry out the grain on the bottom. Indirect heat is best whenever possible.

Can I store a fully colonized bag?

Yes. A fully colonized spawn bag or quick-colonizing 5-grain jar can be stored for up to 3 months in a cool, dark place. Ideal storage temperatures are 55–68°F.

My bag looks dry. Is that normal?

Yes. Spawn bags often look dry on the outside because many grains, especially rye, have an outer husk that does not visibly hold water. Much of the moisture is stored inside the grain itself.

How much spore solution or liquid culture should I inject?

About 5cc total per spawn bag, or 3–5cc per grain jar. Distribute the solution across several injection points rather than concentrating it in one spot — this dramatically speeds colonization.

What if my bag seems stalled at 75% colonization?

Mark the current growth line with a marker and check again after a week. If the mycelium has not advanced and you are ready to move on, you can remove the cake and brush away any uncolonized grain before using only the fully colonized portion in your bulk substrate.

Should I use spore syringes or liquid culture?

Both work. Liquid culture skips the germination step (mycelium is already growing in solution), so it colonizes faster and more consistently. Spore syringes are great for genetic diversity and exploring new strains. For large batches, liquid culture is usually the better choice.

What temperature is too hot for incubation?

Avoid ambient temps above 78°F. Bags generate 3–4°F of internal heat while colonizing, so a 78°F room can mean 82°F inside the bag — high enough to encourage contamination, condensation, and wet spots.

After They Are 100% Colonized

Once your bag is fully colonized, it is ready to be broken up and mixed with bulk substrate. A common recommendation is a 2:1 weight ratio of bulk substrate to grain spawn when preparing a monotub or fruiting chamber.

This next phase is often called bulk growing or a bulk monotub grow. For more detail, continue on to your monotub or bulk growing instructions.

Shop Bulk Substrate Shop Monotubs View More Guides

Fully colonized mushroom spawn bag ready to use

Fully Colonized Spawn Bag

Closeup of fully colonized grain spawn bag

Closeup of Full Colonization

Grower holding a fully colonized spawn bag

Ready for Bulk Growing

Colonized spawn bag and bulk substrate on table ready to mix

Spawn + Substrate Ready to Mix

Bulk Grow Monotub Fruiting

Bulk tub stages of mushroom growth after mixing colonized spawn with substrate

Typical Stages of Bulk Tub Growth

How to Use the 5-Grain & Rye Jars

5-grain and rye jars are very similar to spawn bags, with a few small differences.

Remove and discard the foil before incubation. The foil is only used during sterilization and can restrict proper gas exchange if left on.
Each jar typically does best with about 3–5cc of spore solution.
One 10cc syringe is usually enough for about 3 jars.
When injecting, rotate the syringe and spray some solution against the inside glass in a circular pattern to help distribute the spores or culture more evenly.

Jar Tip

Gravity will slowly pull the solution downward through the grain, helping saturate more inoculation points and often improving germination and colonization speed.