How to Grow Mushrooms in a Rye Grain Grow Bag: A Step-by-Step Guide

Materials You'll Need:

Step 1: Prepare the Rye Grain

Measure your rye grain: Use about 1-2 pounds of rye grain per grow bag. Adjust depending on the size of your bag and your needs.
Soak the grain: Place the rye in a large pot or bucket and fill with water. Allow the grain to soak for 12–24 hours. This softens the grains and begins germination, which makes them easier for the mycelium to colonize.
Boil the grain: After soaking, drain and rinse the grains thoroughly. Then, place them in a large pot, cover with fresh water, and bring to a boil. Let the grains simmer for about 10-15 minutes. You want them hydrated but not mushy—test by squeezing a grain. It should be soft but not burst open.
Drain and dry: Once the grains are properly hydrated, drain the water and spread the grains out on a clean towel or baking sheet to dry. Let them air dry until the surface of the grains is no longer wet (they should feel slightly moist but not sticky).

Optional: Add 1–2 tablespoons of gypsum to the grains during boiling to improve grain texture and reduce clumping.

Step 2: Sterilize the Rye Grain

Fill the grow bag: Once your grains are dried, fill your mushroom grow bag about halfway with the hydrated rye grain. You want to leave enough room for the grain to move around inside the bag as the mycelium grows.
Seal the bag: Many mushroom grow bags come with a built-in filter patch to allow for gas exchange. If your bag doesn’t have an easy-to-use seal, fold the top of the bag and secure it with a rubber band or tie it off, but do not fully seal it—this allows the steam to penetrate during sterilization.
Sterilize the grain in a pressure cooker: Place your grow bag(s) in a pressure cooker and add 2-3 inches of water. Cook at 15 PSI (pounds per square inch) for 90–120 minutes. Sterilizing at this high pressure kills all contaminants like bacteria and mold spores.

Allow the pressure cooker to cool completely before opening, which can take a few hours.

Step 3: Inoculate the Rye Grain with Mushroom Spores or Liquid Culture

Sterilize your workspace: Clean your working area, use rubbing alcohol to sterilize surfaces, and wear gloves to minimize contamination risk. If you have a still air box or glove box, this is the time to use it for the sterile environment.
Prepare your spore syringe or liquid culture: If using a spore syringe, flame sterilize the needle using a lighter until it turns red-hot. Let it cool for a few seconds before use.
Inject the spores: Open the bag slightly (near the top) and inject 2–5 cc of spores or liquid culture directly into the grain. Try to move the syringe in different spots to spread out the inoculation points.

If using jars to inoculate first, inject into a sterilized grain jar and then transfer to the grow bag later.

Seal the bag: After inoculation, fold the bag closed and either heat-seal it (if your bag allows) or clip it shut with a zip tie or rubber band.

Step 4: Colonization (Growing Mycelium)

Store the bag in a warm, dark place: Keep the inoculated bag at a temperature of 70–80°F (21–26°C), which is ideal for most mushroom species. Store it in a dark or dimly lit environment.
Wait for colonization: Over the next 2–3 weeks, the spores will germinate, and white mycelium will begin to grow and spread through the rye grain. You’ll see the grain turning white as the mycelium colonizes it.
Check for full colonization: When the entire bag is white and fully colonized, with no uncolonized grains visible, it’s ready for the next step. This can take 3–4 weeks depending on conditions.

Step 5: Prepare the Substrate for Fruiting

Option 1 - Fruiting in the bag: You can fruit directly in the grow bag by cutting a few slits in the sides of the bag to allow mushrooms to grow through, keeping the bag humid and misting regularly.
Option 2 - Transfer to bulk substrate (recommended): For larger yields, it’s best to mix the colonized rye grain with a bulk substrate like coco coir and vermiculite.

Hydrate the bulk substrate the same way you would in a monotub setup.
In a sterile environment, mix the colonized rye grain with the bulk substrate in a large, clean tub or container.

Step 6: Fruiting (Pinning and Mushroom Growth)

Transfer to a fruiting chamber or monotub: Once the rye and bulk substrate are mixed, place the mixture into a fruiting chamber or a monotub for optimal conditions.

Humidity: Keep the environment humid by misting the walls of the chamber and ensuring the substrate doesn’t dry out.
Light: Introduce 12 hours of indirect light (either daylight or artificial grow light).
Fresh air: Allow fresh air exchange by fanning the tub a few times daily. You can also open and close the bag slightly if fruiting inside the grow bag.

Wait for pinning: After about 7–10 days, you should see small mushroom “pins” forming. These are the baby mushrooms starting to grow.

Step 7: Harvest the Mushrooms

Harvest at the right time: Once the mushroom caps start opening (just before they fully flatten out), they are ready to be harvested. You’ll see them go from small pins to full mushrooms in just a few days.
Twist and pull: Gently twist the mushrooms at the base to remove them. Be careful not to damage the surrounding mycelium or substrate.
Misting and maintenance: After harvesting, keep misting and maintaining the environment for the next flush (more mushrooms will grow in a few days to weeks).

Step 8: Flushes and Final Harvest

Second and third flushes: After each flush, allow the bag or substrate to "rest" for a few days. Continue misting and fanning to encourage new pins to form.
Repeat until the mycelium is spent: You can usually get 2–4 flushes of mushrooms from the same substrate. Each flush will likely produce fewer mushrooms than the previous one.

Step 9: Clean Up and Disposal

Dispose of the substrate: Once the grow bag stops producing mushrooms, you can dispose of the spent substrate in compost or in the garden.
Clean and reuse your tools: Wash your grow bags and any reusable tools to prevent contamination in future grows.

Tips for Success

Sterility is key: Contamination is a common issue. Always sterilize your equipment and work in a clean environment.
Patience is necessary: Growing mushrooms takes time, especially during the colonization phase. Resist the urge to check too frequently.
Monitor humidity: Mushrooms need a humid environment to grow well. Mist regularly, but avoid drenching the substrate.