How to Use Mushroom Grain Spawn - A Beginner's Guide (NZ)

Grain spawn is sterilised grain that has been fully grown through with living mushroom mycelium. It's the "seed" you use to grow mushrooms. 

You mix it into a bulk food source called a substrate, such as pasteurised straw, firewood pellets or sawdust, usually at 5–10% spawn by weight. Over 1–4 weeks the mycelium spreads from each grain through the substrate, and then it fruits to produce fresh mushrooms.

So you've got a bag of grain spawn (or you're thinking about ordering one) and you're wondering: now what, how do I use Mushroom Grain Spawn?

Good news. Grain spawn is the cheapest and most reliable way to grow serious amounts of gourmet mushrooms at home. And using it is much easier than it looks.

We make every bag of our >> mushroom grain spawn right here on our North Canterbury farm, and we've helped thousands of Kiwis take their first steps with it.

We are very proud to have over 1700 independent kiwi reviews with an average of 4.9 stars

This guide covers everything you need to know: what grain spawn actually is, how much to use, what to mix it into, how to identify common contaminants and how to get from a bag of grain to a basket of fresh mushrooms.

What is mushroom grain spawn?

Grain spawn is hydrated, cooked, sterilised grain that has been fully grown through (colonised) with mushroom mycelium (the white, root-like part of the mushroom).

The easiest way to think of it in gardening terms: Grain spawn is mushroom "seeds."

Each grain acts like a tiny food parcel with living mushroom culture attached. When you mix spawn into a bulk food source (called a substrate), the mycelium grows off the grain and spreads through the new material. The mycelium uses the water and nutrients in the grain initially to quickly grow through the substrate, then it eats the substrate to then produce the mushrooms.

All SporeShift grain spawn is grown on locally-sourced NZ wheat and only shipped once it's 100% colonised and contaminant-free. That means it's ready to use the moment it arrives.

Why use grain spawn instead of a kit?

Kits are brilliant for learning, that's exactly what our >> Splash and Grows are for. Once you know the basics, learning to grow from spawn makes mushroom growing far more economical, you can do this using our >>DIY kits and >>refill kits:

• It's cheap per kilo of mushrooms. One kg of spawn can inoculate 10-20 kg of substrate. That's a lot of mushrooms from just $25 of spawn.

• You choose the scale. One bucket on the bench, or twenty bags in the shed. Same method, just more of it.

• More species. Kits mostly cover Oysters. With spawn you can grow Shiitake, Enoki, Tawaka, Turkey Tail, Pekepeke-Kiore (NZ Lion's Mane) and more.

• Feed the whole family or start your own Mushroom Farm. Once you can grow from grain you will easily be able to produce enough mushrooms to feed the whole family, from here all you need to do is increase your scale and you could have your own mushroom farm supplying local markets and restaurants.

  We offer commercial spawn weekly and fortnightly to many farms around the country - if this interests you please get in touch >> contact us here.

If you've never grown mushrooms before, honestly stick with oyster mushrooms, they are the easiest most reliable mushrooms to grow. The >>5 Step Kit teaches you how to use and grow from spawn with full instructions included and everything you need in the kit.

The 5 basic steps of growing from spawn:

Every Grain Spawn Grow follows the same five simple steps:

1. Choose your mushroom and substrate (the spawn and substrate has to match - each spawn product page has this information provided)

2. Prepare the substrate (pasteurise or sterilise it - see each spawn product page for unique recommendations)

3. Mix in the spawn (this is called inoculation)

4. Wait while it colonises (1-4 weeks in a warm, dark spot)

5. Fruit and harvest!

Let's walk through each one.

Step 1 - Match your mushroom to a substrate

A substrate is just the food your mushrooms grow on. Different species like different foods:

• Oyster mushrooms (Grey, Pink, Blue, Pearl, Native Velvet and friends) are the easy ones. They'll happily grow on pasteurised straw or firewood pellets with no fancy gear needed. They also grow well and produce huge yield on sterilised supplemented sawdust. 

• Shiitake, NZ Lion's Mane / Pekepeke-kiore, Tawaka, Enoki and Turkey Tail are fussier. They need fully sterilised supplemented sawdust.

• Shiitake specifically only likes a hardwood with 10-20% bran, we personally use Biobriq's with organic bran for our >> Shiitake Blocks

Beginner tip: start with Oysters on firewood pellets pasteurized with hydrated lime (the DIY Kit Method). A 20 kg bag of pine fire pellets costs about $14 from Bunnings or Mitre 10, and it's the most reliable substrate I've used in nine-plus years of growing.

If sterilising sounds like too much, we've done it for you. Our >> sterilised sawdust blocks arrive cooked and ready to inoculate, so you can grow any species without a pressure cooker.

Step 2 - Prepare the substrate

Raw straw and sawdust are full of moulds, bacteria and spores that will race your mushrooms for the food. Preparing the substrate (pasteurising or sterilising) clears out the competition and gives your spawn a head start.

For Oysters, the cheapest and most reliable method is hydrated lime pasteurisation. Soak your straw or pellets in hydrated lime-treated water, drain, and you're done. No cooking required. We sell >> hydrated lime in the shop, and the full method is in this guide: >> How to Grow Bulk Oyster Mushrooms on Pasteurised Straw.

For everything else, you'll need 90 minutes at 15 PSI in a pressure cooker, with the substrate packed into >> filter patch bags. Please note the 90minutes timer starts from when the pressure cooker reaches 15PSI.

Alternatively you can steam the substrate at 95deg C in a barrel steamer for 12-24 hours.

Not sure which method your mushroom needs? This post explains the whole thing in plain language: >> Pasteurisation vs Sterilisation.

Each spawn product page also has specific substrate recommendations on it.

Step 3 - Mix in your spawn (Inoculation)

This is the fun bit. Break up the spawn bag with your hands (while it's still sealed) so the grains separate, then mix it evenly through your cooled or drained substrate.

How much spawn do I use? The golden numbers:

• 5-10% spawn to substrate is the standard rate. So 1 kg of spawn does 10-20 kg of wet substrate.

• You can use up to 20% if you want faster colonisation and less contamination risk. Great for beginners or cooler months.

• More spawn = faster and safer. Less spawn = cheaper, but slower and more risk of contamination if inoculation area isn't super clean or the substrate wasn't fully pasteurized / sterilised.

Keep it clean. Wash your hands, wipe down your surfaces, and work efficiently. Hydrated lime pasteurised Oyster substrate is very forgiving and can be mixed in open air.

Sterilised substrate is more prone to contamination, so inoculate it inside a >> still air box or in front of a >> flow hood.

Then pack the mixture into buckets or bags with small air holes. Full details on that here: >> How To Grow Oyster Mushrooms in Reusable Buckets and Bags.

Step 4 - Let it colonise

Put your buckets or bags somewhere warm (17-25°C). Your incubation space does not have to be fully dark, but your incubating bags must be out of any direct sunlight. A cupboard, hot water closet or spare room works well.

Over the next 1-4 weeks you'll see white mycelium spreading out in every direction from each grain until the whole substrate turns white. You don't need to do anything during this time. No watering, no checking, no fussing. The mushrooms have got it from here.

One thing to watch for: healthy mycelium is white. If you see green, black or orange patches, that's contamination and it means a competing mould got in. It happens to every grower sometimes so don't be disheartened if you get some contamination while you're learning.

If the competing mould is only small patches and has white mycelium around it - it is generally fine, the mushroom will fight it off, if over 30% of the bag is contaminated the bag should be put outside in the garden to see if the mushroom will fight it off out in nature. This is only true for fruiting substrate and not spawn.

If you are not sure feel free to send us a photo and we are happy to advise!

What Does Contaminated Grain Spawn Look Like?

Contaminated grain spawn can be tricky for new growers to identify but there are a few common contaminants that are easy to spot.

Every grower loses a bag sometimes. Us included! The trick is knowing what you're looking at, because some of the things that scare beginners are completely normal.

Here's how to tell them apart.

Healthy mycelium

For most species it looks bright white, fluffy or rope-like, and it looks mostly dry. It spreads out from each grain and slowly joins up until the whole bag is white. The grains aren't mushy and can be broken back up.

If that's what you've got, you're all good. Carry on.

Please note some species like the Native Hericium (NZ Lions Mane) have very fine mycelium and to the untrained eye the grain will not look super white and overly colonized. Every mushrooms mycelium is actually unique, with different growth density, aroma, grain binding strength etc.

Metabolites (normal, don't panic)

Yellow, amber or golden-brown liquid in the bag of grain with the mycelium. It looks alarming the first time you see it.

It's not contamination. It's just the mycelium's waste, basically mushroom pee, and it's actually a sign your culture is active and working hard. Common in Oysters and completely harmless. Use the spawn as normal.

Wet spot (bacterial blotch)

We set this bag aside on purpose to show you what too much water looks like.

This is the most common failure when people cook their own grain, shown in the two photos below.

Bacillus endospores are highly heat tolerant and do not all die during pressure cooking, they must be germinated during the grain preparation process so they can be killed during grain sterilisation.

Over hydrated grain is a common reason for bacillus contamination. It is also known as "wet spot"

What gives it away:

• Free water pooling between the grains or in the bottom of the bag. Not droplets on the outside of the plastic, but actual liquid in with the grain.

• Grains clumped into a wet, heavy mass instead of sitting loose.

• Grey, slimy or see-through patches through the grain.

• Colonisation stalls. The mycelium goes thin and wispy and stops spreading, leaving bare shiny wet brown grain behind.

• A sour smell like sour milk or rotten apples. This is the giveaway. Healthy spawn smells clean and mushroomy. If it smells sour, that's your answer.

Notice the water sitting between the grains, and how the mycelium has stalled instead of joining up. These grains are likely contaminated with Bacillus

Moulds

Green, black, grey-blue or fuzzy orange patches. Green (Trichoderma) is the most common and often starts white before it turns green, it will only stay white for a day or two before sporulating and going green, so if you're unsure just wait an extra day to find out.

Trichoderma has a super obvious give away before it goes green, it grows super fast and will often make the bag look excessively sweaty with a lot of very fine condensation sitting on the inside of the plastic pictured below.

You can see the very fine water droplets on the spawn bag from Trichoderma contamination - this is just before it goes green and produces spores.

Don't open a mouldy bag indoors - especially a bag infected with green mould Trichoderma. Opening it releases millions of spores that can cause higher risk of future contamination in your mushroom grows. Best just to put it in the bin still sealed in the bag.

You can see the green tinge on all of the grains, that is billions of Trichoderma spores ready to spread. This Spawn is rubbish - there is nothing that can be done to save it.

Quick summary guide:

What you see	What it is	What to do
White, dry, fluffy	Healthy mycelium	Use it!
Yellow or amber liquid	Metabolites	Normal, use it
Water between the grains, sour smell	Wet spot (bacteria)	Bin it
Green, black or fuzzy orange	Mould	Bin it - do not open

Step 5 - Fruit and harvest!

Once your substrate is fully white, it's ready to fruit. Mushrooms need three things to switch from growing to fruiting:

• Fresh air - open holes or cut slits in the bag. DIY kits will already have holes and will fruit when they are ready. Try avoid drafty areas!

• Light - indirect daylight is perfect or as a guide if you can read a news paper thats enough light (no direct sun)

• Humidity - mushrooms grow best around 80-90% humidity.

In 5-10 days you'll see tiny pins form, and a few days later... full mushrooms! Harvest just before the caps flatten out, and cook them up fresh or store in the fridge.

Personally, I love cooking Oysters until they're almost like chips! See my favourite recipe here >> How to Cook Perfect Crispy Oyster Mushrooms

Most bags will fruit again in 1-4 week intervals for many months (we call this flushes).

How to store your grain spawn:

Spawn is a living product, so use it fresh when you can. Ideally within 2 weeks of arrival.

If you need to wait, most species store in the fridge for up to 8 weeks, sometimes up to 4 months +. Simply sit the bag upright with the white filter patch stood up so the spawn can breathe.

Pink Oysters are the exception here. Being a tropical species they hate the cold, so keep them at room temperature (7-20 deg C) in a dark cupboard, break the spawn up each week to stop it fruiting on the spawn before you use it.

Your grain spawn bag will arrive with a printed instruction sheet.

Common questions about grain spawn

How much substrate does 1 kg of grain spawn make?

At the standard 5-10% rate, 1 kg of spawn inoculates 10-20 kg of wet substrate. That's roughly two to four 10L buckets of Oyster mushroom substrate as a guide.

Spawn can be used as low as a 1% ratio but this is not recommended for home growers.

Grain spawn broken up on top and undisturbed on the bottom. It is fully colonized 100% ready to be used

I broke my spawn up now its not white - Is it still ok to use?

This is a super common question we get, the picture shows a bag of fully colonized grain spawn, I have broken the spawn up ontop and left the bottom. You can see the top looks much less white.

Even though it looks less white the mycelium is still there and waiting for more food.

The spawn is 100% fine and ready to use even though it seems less white.

Can I put grain spawn straight into the garden?

Sort of! Grain spawn works well indoors but not outdoors: rodents, birds and insects love the sweet cooked grain and will quickly eat it out in the garden.

For outdoor growing we use >> Sawdust Spawn or >> Mushroom Dowels.

For garden beds species like King Stropharia we use sawdust spawn -- insects and birds won't try to eat the sawdust.

Just don't expect indoor-style results from scattering sawdust spawn on soil, it needs a proper wood-based food source. You can find more information on growing mushrooms outdoors using woodchip and logs here >> How to Grow Mushrooms in your NZ Garden, >> Growing Mushrooms On Logs in NZ

Can I use grain spawn to make more grain spawn?

Yes! It's called grain-to-grain transfers, and it's how you turn 1kg into 20kg or more.

However making grain spawn takes great care and attention to detail, its a delicate process that has very specific requirements.

The grain must be the perfect moisture content otherwise heat resistant bacterial spores that do not die during sterilising will grow, the grain must be fully pressure sterilised and inoculated in front of a laminar flow hood or in a still air box.

We offer >>sterilised grain which we have prepared, sterilised and double bagged, it arrives ready to inoculate. A >>still air box or >>Laminar flow hood is still recommended for reliable grain inoculations.

We also have >>sterilised grain in injection port bags, these bags have a self healing injection port on the bag, simply inject 3-10ml of liquid culture into the grain bag and let the mushroom do its thing! These bags do not even need to be opened.

Inoculating your own spawn is a brilliant next step once you've got a few grows under your belt!

My spawn bag has some brown / yellow ish liquid - is it ruined?

New growers often confuse this with contamination. As the mycelium grows through the grain it begins to digest it. Mushrooms digest their food by secreting enzymes to break it down, this process produces Metabolites which is healthy and normal. Metabolites - basically mushroom pee is the waste product of this external digestion process which appears as a yellow to brown liquid over time.

Green, black or fuzzy orange is not normal. If you're unsure, send us a photo before opening the bag and we will be happy to advise. Unopened contaminated spawn is always replaced - guaranteed.

What's the difference between grain spawn and liquid culture?

Liquid culture is mushroom mycelium grown in a nutrient liquid broth, it is used to inoculate grain spawn (liquid culture is generally not used to inoculate substrate apart from some very specific growing styles like the cultivation of cordyceps mushroom). It's a lab tool we regularly use at the farm.

Grain spawn is the ready-to-go "seed" you mix directly into your substrate. If you want to grow mushrooms rather than make cultures, grain spawn is what you want.

Which mushroom should I grow first?

Grey and Blue Oysters, hands down. Hardy, fast and forgiving from 5-25°C. Still unsure? - I have a detailed blog here to help >> Which Mushroom Variety Should I Grow?

I thought mushrooms grow from spores?

This is true for mushrooms out in the wild but not when growing mushrooms to eat. Sporeshift holds an MPI Permit to import approved specific mushroom strains with desirable growth traits and characteristics such as good yield, shelf life, taste and texture.

Overseas companies like Mycelia in Belgium breed commercial strains which are available to us for cultivation. These strains are selected out of mass breeding programs from decades of work. Where as growing from spores will produce random results and sometimes even mycelium that is not capable of producing a fruit body to eat.

Sporeshift maintains an extensive library of cultures we have hand selected and tested in house and are continually working with.

Ready to grow?

Learning to grow from grain spawn is where mushroom growing shifts from a fun project to a genuine food supply.

Start small, keep it clean, and don't be scared to make mistakes. Every grower loses a bucket now and then, including us.

Grab a bag of >> A-Grade grain spawn - 16 varieties, 100% colonised on NZ wheat, shipped fast NZ-wide.

If you get stuck along the way, flick us a photo. Helping Kiwi growers succeed is what we're here for.

Always identify any mushroom before consuming!