Spawn It

What spawn really is

Your substrate is clean and cool. Now it needs a living starter. That starter is called spawn.

Spawn is any material that is already colonised — that is, already threaded through with living mushroom mycelium, the fine white web that is the mushroom's body. Think of spawn as a seed for mushrooms. You mix a little colonised material into a lot of fresh substrate, and the mycelium spreads out from those pieces to claim the whole batch.

Where your spawn comes from

You do not need to buy anything new. A great source is the grow kit you already used.

• A piece of your old, fully colonised kit block — the parts that are solid and white with mycelium — can act as spawn.

• Some growers save a healthy chunk before the block wears out, breaking it into smaller pieces.

Using kit material has a big safety advantage: you know exactly what species it is. It is oyster mushroom, a known, safe kind. You are never guessing, and you never use anything gathered from the wild.

How much to add

More spawn means a faster, safer colonisation, because the mycelium has more starting points to spread from and less time for moulds to sneak in. A common guide is to add spawn equal to about one part spawn for every ten parts substrate by weight — for example, a small handful of colonised material into a container of your coffee-and-straw mix.

If you can add a bit more spawn, that is usually even safer for a beginner. The more of the food that mycelium reaches quickly, the less room competitors have.

Clean hands, clean mixing

This is the moment competitors are most likely to slip in, so cleanliness matters.

1. Wash your hands well, then dry them on a clean towel.

2. Work on a wiped-down surface, away from open windows and fans that blow dust around.

3. Break the spawn into small crumbs and mix it evenly all through the cooled substrate. Even spreading means the mycelium starts from many points at once.

4. Pack the mix gently into a clean container or bag — firm enough to hold together, loose enough to keep some air.

Make sure the substrate has fully cooled first. If it is still warm from pasteurizing, the heat can harm the delicate mycelium you just added.

Give it air, keep out pests

Mycelium needs to breathe, but you do not want flies laying eggs in your grow. A few small holes, or a breathable filter patch, lets air move while keeping pests out. Your kit's own bag design is a good model to copy.

The golden rules still hold: only known kit species, never wild mushrooms, and any mushroom you eat is cooked by an adult, never eaten raw.

You have inoculated your own substrate — that means you added the spawn. Now the mycelium takes over. In the last lesson, we wait and care for it.