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Different Types Of Grain Spawn

When making grain spawn, the gold standard has always been rye grain. And that makes sense. Rye is widely available, hydrates well- and is universally loved by almost any mushroom species. But what if you can’t get rye grain? Is there any other grain that’s up to the task? Definitely. In fact, you can make amazing spawn out of a variety of different grains, some of which you probably have in your pantry right now.

What Is Grain Spawn?

Grain spawn can be thought of like “seeds” in mushroom cultivation. It is made by starting from either spores or a mushroom culture, which is then transferred to sterilized grain. The mushroom mycelium then grows throughout the grain, feeding off the starchy goodness. Eventually, the mushroom culture will fully colonize the grain, covering it in white mycelium. From there, it can be broken up into individual grain kernels and mixed into a bulk substrate. The mycelium will continue to grow from there- eventually producing mushrooms.

Why Does It Have To Be Sterilized?

Grain is highly nutritious- full of starch and sugars. When properly hydrated, it serves as an ideal food source for hungry mushroom mycelium. Unfortunately, this also an ideal growing environment for mold and bacteria- which in most cases can grow much faster and stronger than mushroom mycelium. For that reason, the grain has to first be completely sterilized in order to kill off any mold spores or bacteria. This is most often accomplished in a pressure cooker or autoclave by processing at 15PSI for 1.5 - 2.5 hours. Pure mushroom mycelium added to sterilized grain has no competition, which allows it to grow and proliferate throughout the grain.

Different Types Of Grain Spawn

So what’s the best type of grain spawn for you? Unless you are running a commercial farm, the best grain spawn is often what is available to you.

Rye Grain

If you have access to Rye, it will be your best choice most of the time. It’s excellent at holding water (can hold more moisture than any other grain), and doesn’t often burst or get mushy when processed. Also, mushrooms of all types seem to absolutely love rye as a source of nutrition. That being said, unless you’re located near a farming community, it can be hard to find. You are also not likely to find it in small amounts at the grocery store, so it might not be the best choice for a small hobby grower.

Wheat Berries

Wheat berries (ie. wheat grain, wheat seeds), are also an excellent choice, and perform very similar to rye. They can be prepared using the exact same method as rye grain. The difference is that wheat cannot hold as much water, and are more likely to break when processed. You can often find organic wheat berries at bulk food stores.


Barley is yet another cereal grain that works (kinda) for spawn. You can tell by the picture that it is certainly not ideal. Mushy and, wet, and lots of broken grains.


Sorghum is commonly used by commercial growers. In other industries, Sorghum is used in animal feed. For that reason, commercial spawn producers can get non-human grade sorghum grain cheaply to be turned into spawn.


Millet is another wonderful grain for mushroom spawn. Millet is the smallest of the grains, and provides a huge number of different “inoculation” points in your substrate. Since it is so small, it is most often mixed with other grains to make spawn.

Brown Rice

Brown rice tends to get a little mushy/sticky when processed, and for that reason, it is typically not used by commercial growers. For small scale hobby growers, however, brown rice can be a suitable choice. Can I Use White Rice? Although I wouldn't blame you for trying, I just can't recommend white rice. It is much to sticky and mushy, and will likely end up as a large clump after processing.


Popcorn spawn is actually pretty good. Of course, it's expensive compared to the other grains- but you can easily find it at the grocery store. You might even have it in your cupboard already! Compared to other grains, popcorn is huge- meaning you are going to get significantly fewer inoculation points. It also takes a much longer time for the mycelium to colonize it- not only because the grains are large, but because there is larger gaps for the mycelium to “jump” across when colonizing.

Wild Bird Seed

Wild Bird Seed (WBS) is commonly used by hobby growers, mainly because you can get a huge bag of it for cheap at any garden center or hardware store. You would definitely not see commercial growers using birdseed. It's is inconsistent, doesn’t hydrate evenly and isn’t universally loved by all mushroom species. That being said, if you don’t have access to other grains, wild bird seed will work. Just look for bird seed that doesn’t have sunflower shells in it. (that can be hard to find)

Should Grain Spawn Be Organic?

If you can get organic grain, then sure... why not? Especially if you are buying large bags of rye grain, sorghum or millet. For things like popcorn, brown rice, and wild bird seed you shouldn’t really worry about it. I’m not an expert in this area, but it’s possible that some grains could be sprayed with fungicides- obviously not ideal for your mushrooms.

Other Types of Spawn

Grain spawn is amazing for mushrooms and is the most common material used for first-generation spawn. But it’s not the only way to propagate mushroom mycelium through subsequent generations.

Sawdust Spawn

Sawdust spawn is often used for second-generation spawn for a couple of reasons.
  • It’s not as nutritious, so not as prone to contamination.
  • It’s great for outdoor beds, and less prone to attract rodents and other critters.
  • It “trains” the mycelium to eat hardwood, which is helpful when transferred to supplemented hardwood fruiting blocks.
The downside of sawdust spawn is that it takes longer to colonize. It also has less nutrition, which can result in a smaller yield when the mushrooms finally fruit.

Synthetic Spawn

Synthetic spawn is commonly used by Agaricus growers (button mushrooms) and produced by a few large spawn companies. It is highly particulate, colonizes fast, and is more resistant to contamination than traditional grain spawn.
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