Mushroom Grow Bags UK

Mushroom grow bags do two jobs: they hold your substrate while it colonises, and they hold humidity once it is time to fruit. Get the right bag for the job and a lot of the fiddly equipment other methods need simply disappears.

Why a filter patch bag beats a jar

A filtered grow bag lets the mycelium breathe without letting contaminants in. The filter patch handles gas exchange passively, so there is no daily fanning, no lid to lift, and no repeated opening — and every time you do not open something, you remove a contamination risk.

Our Unicorn bags are rated for pressure cooker and autoclave sterilisation up to 136°C, so you can sterilise substrate straight through the bag rather than decanting it afterwards while it is still vulnerable.

Never spray alcohol onto a filter patch. That patch is how the bag breathes. Soaking it can block it, or carry contaminants straight through.

Choosing the right bag size

Bag size follows the job, not ambition.

Type 4T-Inj, 1-2lb — the small-batch option. Good for testing a culture, running several genetics side by side, or working in a small space where a big bag will not fit on the shelf.

Type 10T-Inj, 1-5lb — the workhorse for grain spawn making. Injection port fitted, so the bag never has to be opened to inoculate.

XLS, 2-6lb — for fruiting, cakes and bulk substrate. This is where the yield happens.

Using the injection port properly

An injection port is a self-healing seal that lets you introduce culture without opening the bag. Used properly it is the single biggest contamination saving in the whole process.

Wipe the port — and only the port — with the supplied alcohol swab, let it dry, then inject through the centre.

Never heat or wipe the needle when inoculating bags with injection ports. Our needles arrive gamma-irradiated sterile in sealed packaging. Flaming or wiping does not improve on that; it adds soot, residue and handling risk. Take it out of the wrapper and use it.

Full detail on clean working is in How to Avoid Contamination Growing Mushrooms.

Sealing bags for the autoclave

If you are filling your own bags, they need sealing before they go into the pressure cooker. Our Easy Glide Bag Sealers come in 12.5cm and 18.5cm and withstand pressure cooker and autoclave temperatures up to 136°C — an ordinary clip will not survive that.

Sterilise for 3 hours per kilo at 15 PSI, and remember that the time is set by the size of each individual bag rather than how many you fit in the cooker. Ten 1kg bags in one run is still three hours.

Easy Glide Bag Sealers: Sealing Bags for the Autoclave

Keeping the temperature right

Bags colonise best at a stable temperature, and the target depends on what is inside rather than what the bag looks like:

Inject & Forget bags (brown rice flour and vermiculite) — 26°C
Grain-based bags and rye grain spawn — 22°C
LightBags (rye grain and coco coir) — 22-23°C

Allow about ±1°C either side. If you are using a warming mat, the probe goes under the bag on the mat, not taped to the side. That is the most common heat mat mistake we see.

Common mistakes with grow bags

Opening the bag to check on it. You can see everything you need through the plastic.
Spraying disinfectant on the filter patch. Port only, always.
Using a clip or heat sealer not rated for autoclave temperatures. It will fail at pressure, usually messily.
Standing a large bag upright as a deep block. Lay it flat and reasonably thin — it colonises far more evenly.

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All MushBuddies products are sold for legal mushroom cultivation, microscopy and taxonomy use only.