Grow Guide
How to inject your spawn bag cleanly — and what to do from that moment until full colonisation. This guide focuses on what happens after the needle goes in.
Written by the Cloud920 mycologist
Last updated: April 2026
7 min read
If you're using a Cloud920 sterile spawn bag, the substrate is already sterilised and the injection port is in place. Your job is to add the culture cleanly and then manage the bag until it's ready for fruiting.
The inoculation itself takes less than two minutes. What comes after — temperature, timing, break and shake, reading the bag — is what most growers get wrong the first time. That's what this guide is really about.
What You Need
-
A sterilised spawn bag with injection port -
A liquid culture syringe or spore syringe -
70% isopropyl alcohol (IPA) and paper towels or cotton swabs -
A lighter -
A clean, still environment (still air box ideal, clean counter sufficient)
No laminar flow hood. No pressure cooker. The injection port handles sterilisation at the entry point.
The Inoculation: Quick Reference
The steps below cover everything you need for a clean inject. If you want more detail on technique — what good liquid culture looks like, how much to use, how to split a syringe across bags — read the full How to Use Liquid Culture guide.
Prepare your space
Close windows, turn off fans, let the air settle for 10–15 minutes. Wipe your work surface with IPA.
Flame the needle, wipe the port
Heat the needle until it glows red. Cool 10–15 seconds — don't wipe it. Then clean the injection port with IPA and let it dry.
Inject slowly through the port
Liquid culture
3–5ml per bag. Shake the syringe first to distribute the mycelium.
Spore syringe
2–3ml per bag. Expect a slower start — spores need to germinate first.
Remove, seal, label
Pull the needle out — the silicone port self-seals. Write the strain name and date on the bag. Don't shake or move it for the first hour.
After Inoculation: Managing Your Bag to Full Colonisation
Temperature — the single most important variable
Place the bag in a warm, dark location. Temperature controls everything — colonisation speed, contamination risk, and mycelium vigour. Too cold and growth stalls. Too warm and contamination takes hold.
| Species type | Ideal colonisation temp |
|---|---|
| Psilocybe cubensis varieties | 21–26°C (70–79°F) |
| Panaeolus cyanescens (Jamaica) | 24–28°C (75–82°F) |
| Lion's Mane, Reishi | 18–22°C (65–72°F) |
| Below 18°C (any species) | Colonisation slows or stalls |
A heat mat with a thermostat is the most reliable solution if your home runs below 20°C — especially in winter. Use a folded towel as a buffer between the mat and the bag.
What to expect, day by day
Colonisation timelines vary by substrate, temperature, and inoculation method. Use this as a guide, not a deadline.
Nothing visible. Mycelium is establishing itself at the injection site. Don't disturb the bag. Some condensation on the inside of the bag is completely normal.
First signs of white, fluffy growth appear around the inoculation point. Healthy mycelium is bright white and slightly fuzzy — not flat or slimy. Liquid culture shows first signs earlier than spores.
Mycelium spreads across the substrate. At around 30% coverage, do a break and shake (grain bags only — see below). Full colonisation follows within 1–2 weeks of the break and shake.
The entire substrate is covered in white mycelium, no brown patches visible. Grain bags feel firm and solid when squeezed. CVG bags are fully white throughout.
Break and shake
Grain bags only
The break and shake is the single most effective thing you can do to speed up colonisation. Done at the right time, it can cut days off your colonisation period.
When
When 25–35% of the bag is white. Don't wait for 50% — early is better.
How
Gently massage the outside of the bag to break up the colonised grain and redistribute it throughout the uncolonised grain.
After
The bag will look disrupted for 1–2 days, then recover quickly. Full colonisation typically follows within 5–10 days.
"These bags colonize quick!! I did a BnS a week after inoculating and it bounced back and fully colonized within 3/4 days. I couldn't believe how fast it was."
— Al Kilmer, Cloud920 customer
CVG bags don't need a break and shake — the mycelium spreads through the substrate differently. Leave CVG bags undisturbed until full colonisation.
Reading your bag — normal vs not normal
Most growers who contact us worried about their bag are looking at something completely normal. Here's the quick reference.
Bright white, fluffy growth
Healthy mycelium. Exactly what you want.
Yellow or brown liquid pooling
Metabolite secretion — a normal stress response. Not contamination. Leave it.
Blue bruising on the mycelium
Oxidation of psilocybin when the bag is handled. Normal and expected with cubensis.
Condensation on the inside of the bag
Normal, especially in the first week. The bag is breathing.
Very slow growth, no contamination
Almost always temperature. Check your thermometer and warm up the bag before assuming anything else is wrong.
Green, black, or pink patches
Contamination. Remove the bag from your grow space immediately, seal it in a bin bag, and dispose of it without opening indoors.
Slimy or wet texture with unusual colour
Bacterial contamination. Same action — remove immediately. Don't open indoors.
Not sure what you're looking at? Take a photo of the bag held up to a light source and send it to us. We'll tell you straight.
Colonisation complete — what's next
A fully colonised bag is white throughout with no brown substrate visible. What you do next depends on which bag type you used:
Millet or corn grain bags
Mix the colonised grain into a bulk fruiting substrate — typically a CVG bag. The colonised grain acts as spawn. Use a 1:3 ratio (one part grain to three parts CVG).
CVG substrate bags
Initiate fruiting directly. Move the bag to fruiting conditions — lower temperature, fresh air exchange, and indirect light. Pins should appear within 1–2 weeks.
Frequently Asked Questions
Ready to start your grow?
Sterilised, tested, and ready to inoculate.
Our spawn bags are prepared in-house by an experienced mycologist using organic, A-class ingredients — sealed with an injection port before they leave our lab. Ships fast across Europe from the Netherlands.
Related guides
How to Use Liquid Culture
Full inoculation walkthrough — what LC is, how much to use, how to store it.
Spawn Bag Not Colonising?
Diagnose and fix the six most common reasons a bag stalls or fails.
Millet vs Corn Grain Spawn
Which substrate gives you faster colonisation and heavier yields?
What Is CVG Substrate?
What to do with your colonised grain bag — mixing ratios and fruiting setup.