Grow Bags

Everything you need to know about inject-and-forget grow bags — buying pre-made bags or making your own from scratch.

What Are Inject-and-Forget Grow Bags?

Inject-and-forget grow bags are self-contained growing vessels — typically heat-sealed bags with a built-in filter patch for gas exchange and a self-healing injection port for inoculation. They contain pre-sterilised grain, substrate, or both, ready to receive spores or liquid culture.

The concept is simple: inject your spore syringe or liquid culture through the port, seal the hole, and wait. The bag does the rest. No pressure cooker, no still air box, no complicated sterile work. This makes them hugely popular with beginners and growers who do not have access to a pressure cooker.

Types of Grow Bags

Using Pre-Made Grow Bags

What to Look for When Buying

Not all pre-made bags are equal. Here is what matters:

Storing Bags Before Use

If you are not inoculating immediately, store your bags in a cool, dry, dark location. A cupboard or wardrobe at room temperature is fine. Avoid direct sunlight, damp areas, and anywhere with temperature swings. Check any printed expiry date — most vendors recommend use within 4–8 weeks of manufacture.

Inoculation with a Spore Syringe

This is the most common method for beginners. Follow these steps carefully:

1. Clean your workspace. Wipe down the table, your hands, and the outside of the bag with isopropyl alcohol (70%).
2. Wipe the injection port with an alcohol-soaked cotton pad. Let it dry for 10 seconds.
3. Flame-sterilise the needle. Hold the needle in a lighter or alcohol lamp flame until it glows red-orange. Let it cool for a few seconds — do not blow on it.
4. Shake the spore syringe vigorously for 10–15 seconds to distribute the spores evenly in the solution.
5. Inject 2–5 ml of spore solution through the self-healing injection port. Push the needle in about 1–2 cm. Inject slowly.
6. Seal the injection hole with a small piece of micropore tape as extra insurance, even though the port is self-healing.
7. Place the bag in a warm, dark location at 24–27°C (75–80°F) for cubensis. A cupboard, wardrobe shelf, or box works well. Avoid direct sunlight.
8. Wait for colonisation. You should see the first signs of white mycelial growth within 7–14 days. Full colonisation of the grain layer typically takes 3–6 weeks.
9. Mix/break the bag when the grain layer is fully colonised (all white). Gently break up the colonised grain through the outside of the bag and mix it into the substrate layer. This is the same concept as break-and-shake with jars.
10. Wait for recolonisation. After mixing, the mycelium will recolonise through the substrate. This takes 1–2 weeks.
11. Introduce fruiting conditions. When the substrate is fully colonised (all white), you can either open the top of the bag, cut holes, or transfer the colonised block to a monotub for fruiting.

Inoculation with Liquid Culture

The process is identical to spore syringe inoculation with two key differences:

• Use only 2–3 ml of liquid culture per bag (less than a spore syringe because LC contains living mycelium, not dormant spores).
• Colonisation is much faster — expect 2–3 weeks for full grain colonisation versus 4–6 weeks with spores. This is because liquid culture contains active, growing mycelium that immediately begins colonising, while spores must first germinate.

If you have a choice between a spore syringe and liquid culture, always choose liquid culture. It is faster, more reliable, and gives you a significant head start against contamination.

Common Problems with Pre-Made Bags

Making Your Own Inject-and-Forget Grow Bags

Once you have a pressure cooker, making your own grow bags is significantly cheaper than buying pre-made bags and gives you full control over grain quality, substrate composition, and bag size. A single bag costs roughly a tenth of the price of a pre-made one.

Equipment Needed

Recipe 1: All-in-One Bag (Grain + CVG Substrate)

The all-in-one bag is the closest to the pre-made "inject and forget" concept. It contains both grain and bulk substrate in a single bag — the user injects, colonises the grain, mixes, and fruits.

Ingredients (per bag)

Layering

There are two approaches:

• Layered (recommended for beginners): Place prepared grain in the bottom of the bag, then add the hydrated CVG substrate on top. The mycelium colonises the grain first, then you mix (break and shake) the bag to distribute grain into the substrate.
• Mixed: Combine grain and substrate together before loading the bag. This can colonise faster because the grain is already distributed throughout. However, it is slightly riskier because any contaminant has immediate access to the nutritious substrate.

Recipe 2: Grain-Only Bags

Grain-only bags are simpler to prepare and more versatile. Once colonised, you spawn the grain to a monotub with bulk substrate.

Ingredients (per bag)

• 1 kg prepared rye berries per bag (prepared as per the Grain Spawn guide).
• That is it. No substrate, no additives.

Grain-only bags colonise faster than all-in-one bags because there is less volume to colonise, and the grain-only environment is more favourable for rapid mycelium growth. Once fully colonised, break up the grain and spawn to a monotub following the Spawning to Monotub guide.

Recipe 3: Supplemented Sawdust Bags (Gourmet/Medicinal)

Supplemented sawdust is the standard substrate for gourmet and medicinal species like oyster mushrooms, lion's mane, and shiitake. The most popular recipe is called "masters mix".

Masters Mix Recipe (per bag)

Assembly Step-by-Step

This process applies to all bag types (all-in-one, grain-only, and supplemented sawdust).

1. Prepare your grain or substrate according to the relevant recipe above.
2. Load the mixture into a unicorn bag. Do not overfill — leave at least 15 cm (6 inches) of empty space at the top of the bag. You need this space for folding, sealing, and gas exchange.
3. Fold the top of the bag into a pleat (also called a gusset fold). Flatten the bag, fold the top edges inward to create a clean, flat top section.
4. Position the filter patch. Make sure the filter patch is facing outward and is not folded over or blocked. The filter must be exposed to air for gas exchange during colonisation.
5. Seal with the impulse sealer above the filter patch. The seal should be straight, complete (no gaps), and above the filter — the filter must remain inside the sealed bag.
6. Place bags in the pressure cooker. Fold bags to fit if needed. Do not block the filter patches — the bags need to vent during sterilisation. Place bags upright or at an angle, not flat on top of each other.
7. Sterilise at 15 PSI:
   • Grain bags and all-in-one bags: 90 minutes at 15 PSI.
   • Supplemented sawdust bags: 2.5 hours at 15 PSI (the supplement requires longer sterilisation).
8. Let cool completely. Turn off the heat and allow the pressure to drop naturally. Leave the bags in the cooker for at least 12 hours — overnight is best. Opening early risks contamination from non-sterile air rushing in, and the bags must be at room temperature before inoculation.
9. Apply the self-healing injection port sticker. Once the bags are completely cool, apply a self-healing injection port sticker to the outside of the bag. If using RTV silicone, apply a blob over a small hole and let it cure for 24 hours before use.
10. Ready to inoculate. Your bags are now sterile and sealed with a filter for gas exchange and a port for injection. Inoculate following the spore syringe or liquid culture instructions above.

Strain-Specific Bag Recommendations

Fruiting from the Bag vs Transferring to a Monotub

Once your bag is fully colonised, you have two options for fruiting: fruit directly from the bag or transfer the colonised block to a monotub.

Option 1: Fruiting from the Bag

This is the simpler option and works well for gourmet species and small cubensis grows.

1. For top-fruiting: Cut the top of the bag open and roll down the sides to create a "collar" around the substrate block. Mist the surface lightly once or twice daily.
2. For side-fruiting (oyster, lion's mane): Cut 5 cm "X" shapes in the sides of the bag where you want mushrooms to grow. Mist the cuts daily.
3. Place the bag in your fruiting chamber or monotub with the controller managing humidity and FAE.
4. Harvest when ready and continue misting for subsequent flushes.

Option 2: Transferring to a Monotub

This gives larger harvests but requires more work and exposes the colonised grain to potential contamination during the transfer.

1. Prepare your bulk substrate (CVG) in a separate container as per the Substrate Preparation guide.
2. Open the bag and break the colonised grain/substrate into small chunks.
3. Mix with fresh bulk substrate in your monotub at a 1:2 to 1:4 spawn-to-substrate ratio.
4. Apply a thin casing layer on top if desired.
5. Seal the tub and wait for recolonisation (5–10 days), then introduce fruiting conditions.

Comparison

Grow Bag to SH-Room Controller — Complete Workflow

Here is the complete process from bag to harvest using your SH-Room controller:

Alternative: Fruit Directly from the Bag

If you don't want to transfer to a monotub, you can fruit directly from the bag inside your SH-Room chamber:

1. Once the bag is fully colonised, cut the top open or cut 2-3 X-shaped slits in the sides.
2. Place the bag inside your monotub chamber.
3. Select your strain on the controller and start at the Pinning phase (skip Colonisation since the bag is already colonised).
4. The controller manages humidity, FAE, lighting, and temperature automatically.
5. Harvest when ready. For subsequent flushes, soak the bag for 6-12 hours, then restart at Pinning.

Which Strains Work Best with Grow Bags?