Spawn is mycelium, which has been grown on some sort of substrate, often grain, for the sole purpose; of inoculating more substrate. A bag of spawn is not intended to directly grow mushrooms itself, it’s a bag of inoculant. Having great spawn is a critical part of growing great mushrooms.
Spawn comes in all different types. You can have dowel spawn, grown on little wooden dowels for log cultivation, you can have sawdust spawn grown on sawdust, you can even have popcorn spawn, grown on popping corn. The most common type of spawn is called grain spawn and the most common grains used are wheat, barley or millet or a mix of those grains.
If you look closely at the photos you can see the grain, the mix of grass seeds, and the white fuzzy stuff, which is the mycelium growing through the grain.
We don't produce spawn for sale ourselves at Milkwood, but over the years from the feedback of thousands of students from our Home Mushroom Cultivation course, we've gotten to know the best suppliers of mushroom spawn
Aussie Mushroom Supplies – the best Australian source of grain spawn. You can purchase any of the "Mushroom Spawn Bag 1.7kg" varieties on the linked page.
Disclosure: Milkwood has partnered with Aussie Mushroom Supplies to provide the best type of spawn for beginner growers. The link above is an affiliate link, if you use it to buy spawn, Milkwood will be paid a commission. This does not change the price you pay at all, and by buying your spawn this way you are supporting two small businesses. Thank you.
Field & Forest – a good source of grain spawn located in Wisconsin, USA.