Ask ten growers which grain is best and you will get eleven answers, most of them about rye. Rye is a fine grain and we do not bag it; what we bag is wheat, oats, corn and milo, because all four hydrate evenly, sterilise reliably and give the mycelium what it needs. What differs is the size of the kernel, which drives three things: how many inoculation points you get per kilo, how fast the bag colonises, and how easily it breaks up when it is time to spawn.

The three numbers that matter

Inoculation points

Every colonised kernel is a point from which mycelium jumps into the substrate. Small kernels mean more points per kilo, which means faster, more even spawn runs.

Break-up

How easily colonised kernels separate from each other. Grains that clump need more kneading and leave lumps in the substrate.

Reserves

How much food each kernel carries. Big kernels keep feeding the mycelium longer, which some growers like for slow species and long storage.

Wheat: the all-rounder

Small, even kernels, plenty of inoculation points, breaks up well and colonises quickly with every species we have run through it. If you are not sure, buy wheat. It is the grain the grow builder assumes and the one most of our own tubs start with.

Oats: loose and easy

Whole oats keep their husk, which does two useful things: kernels stay separate instead of sticking together, and the bag shakes apart with almost no effort once it is colonised. That makes oats the best grain for an all-in-one bag, where you have to mix spawn through substrate without opening anything. Inoculation points are similar to wheat.

Corn: big kernels, big reserves

Corn kernels are five or six times the size of wheat, so a kilo carries fewer, bigger inoculation points. Spawn runs are a touch slower to knit together, but each kernel is a reservoir, which suits slower, hungrier species and spawn that will sit for a while. Corn is also the easiest grain to read: a contaminated kernel stands out.

Milo: small, round, tough

Milo is sorghum. Tiny, hard-shelled, round kernels that hold their shape through sterilisation, break up instantly and give the most inoculation points per kilo of the four. Spawn runs on milo are fast and even. The hard shell is also why it tolerates a break-and-shake better than any other grain. If speed is the priority, this is the grain.

Does the species care?

Less than the grower does. Oysters, lion's mane, shiitake, king oyster and reishi all colonise all four grains. The practical differences are speed and handling, not success. Lion's mane is a little slower on grain whatever you give it, and some growers find it a touch happier on oats; shiitake is slow on all of them and is usually taken to agar and then straight to a hardwood block anyway.

The grain guide on the home page

The grain guide scores each grain on kernel size, inoculation points and break-up with the meters you see above, and lets you add the cheapest bag of your pick straight to the basket. If you are filling a tub, the grow builder will tell you how many bags of it you need.

Written by the Aus Myco Kingdom crew. Everything here is general growing information for gourmet and medicinal species; your room, your climate and your culture will have the final say.