How To Grow Mushrooms. Sort Of.

So, you may be new, and asking… how do I grow mushrooms? Honestly, the full answer is beyond the scope of a single blog post. That said, hopefully I can go over some basic concepts in an easy to understand way. Core concepts glossed over here will be explored in future articles.

To grow mushrooms, you will need three basic things:

  • A culture of what you want to grow. This could be a culture on agar, a liquid culture syringe, or possibly even stem butts from purchased mushrooms grown out on cardboard.
  • Spawn. Either purchased spawn, which will already be colonized and ready to use (in which case you can skip the culture), or spawn you produced yourself, which is basically hydrated grain that’s been sterilized in a pressure canner (there’s a lot of steps you can skip or do halfway, but sterilizing grain is absolutely not one of them.) Consider this “baby food” for the culture. It won’t fruit well from spawn, but it’s highly nutritious and your mycelium will tear through it quite quickly.
  • Substrate. This is what the mushroom actually fruits in. If it were a plant, this would be the soil, but we’re gonna stop the plant metaphors right there because most of them are super inaccurate. For many gourmet mushrooms, this will be sawdust, either as sawdust itself or in the form of hardwood fuel pellets. Straw can also be used with oyster mushrooms. This is what the mushroom would be growing on on nature, and this is what the mushroom will fruit from after you inoculate it with spawn. Most substrate is either pasteurized (with heat or chemical methods) or sterilized.

You’ll also need somewhere to fruit your mushrooms once your substrate is colonized, but we’ll worry about that later since depending where you live, you might just be able to put them outside and forget about it.

Your culture, if you’re making your own spawn and not purchasing it pre-made (which is a good option if you’re starting out and don’t have much of a lab setup), will probably be in the form of either a culture on agar, or a liquid culture, which look like this.



The purpose of the culture is to inoculate sterilized grain. Attempting to inoculate the fruiting substrate directly with the culture is unlikely to work, and if it did, would take so long to colonize without the extra nutrients from the grain that it would be likely to contaminate.

Starting out, you may have a choice of which to buy – liquid culture or an agar plate. If you have experience with aseptic technique and a semi-sterile setup (either a still-air box, or a flow hood), I would recommend agar. If not, I would recommend liquid culture, since it doesn’t require you to open the jars in a non-sterile environment for inoculation, and you can get quite a bit of good grain spawn from a 10cc syringe of live mycelium.

Mycelium is white, generally. This is the sort of “vegetative” form of the mushroom that will later turn into an actual mushroom. Some mycelium is thick, some is wispy, but for 90% of gourmet species, it’s white. You can basically gauge how much of a container is colonized by how much has turned white.

NOTE: We’re glossing over sterile technique entirely. This is an overview, not a step by step guide.

If you have a pretty sterile place to work, you can just cut some wedges (thumbnail size) from your agar plate and very carefully drop them into your grain and gently shake it up a bit. After a few days, the mycelium will grow from the agar wedges onto the nearby grains, which looks like this.


This is in a filter patch bag, but it doesn’t really look any different in jars. If you used a liquid culture instead of agar, it’ll honestly look pretty similar, just perhaps in a different pattern where the culture dripped down the side of the bag or jar. When maybe half of it is white, give it a decent shake to distribute the already-growing mycelium to the entire container, and it should speed up from there. Be patient. Eventually your entire spawn bag or jar will be white and fully colonized.

Eventually you’ll end up with something like this. A small amount of yellowish metabolite is nothing to worry about. Colors like green and black, you might have a pretty big problem on your hands and the spawn should probably be discarded somewhere outside. Birds will happily eat it and it would be good for your garden or compost.


If you went the route of purchasing pre-made spawn, you’re already at this step, congratulations!

At this point you have two options. You can use your grain spawn to make more grain spawn by just adding it to hydrated and sterilized grain at about 10% by weight, if you have a still-air box or flow hood, or you can put it directly to the fruiting substrate. I usually do both – I use a bag of grain to make 4 more bags of grain, and also to make 10 or 15 fruiting bags. It’s good practice to only transfer to other grain maybe 3 or 4 times – eventually the mycelium becomes too accustomed to a single food source, and will not perform well.

To use the grain spawn, break it up by either mashing the sealed bag around, or by hitting the jar against something solid but soft (such as a bike tire.) Please don’t whack jars onto your hand, after repeated sterilization cycles the glass can get brittle, and this can end very poorly. If you left your spawn sitting a little too long, this can be challenging if it’s in a jar. Ideally you want the grain such that it could be easily poured.

At this point you’ll need prepared substrate bags or other containers – with fuel pellets, you can often get away with simple pasteurization (hydrate bags of pellets in a camp cooler with boiling water, let sit overnight, once cool, inoculate), or if you’re growing species that take a lot of time (shiitake, etc), sterilized in a pressure canner at 15 PSI for two hours. That’s the subject of another post entirely, and you can also find good information online.

I tend to inoculate substrate bags at about 5% by weight with grain spawn – so if I have a 5 pound bag of sawdust (which is pretty standard), I use about a quarter pound (1 cup or so) of spawn. You can use more or less, using more will make it colonize faster, using less will save spawn. You’ll find a happy medium. Once you’ve inoculated the substrate bags in whatever sterile-ish area you have, seal them (either with a heat sealer or a very tight zip tie) and give them a very good shake to evenly distribute the spawn in the fruiting substrate. Put them somewhere to colonize – conditions aren’t important, anything approximately room temperature is fine, light or dark doesn’t really matter.

As mentioned before, you’ll be able to tell how far along it is by how much of it has turned white. This is a sawdust-based fruiting bag approximately one week after inoculation with grain spawn.


Again, colors like green or black generally indicate you have a problem and that you might have to abandon that bag.

At some point the bag will be fully white, and ready to start producing mushrooms. That will probably look something like this. Shiitake looks quite different, but that’s a discussion for another post.


At this point, you’ll need to make slits in the bag to expose the mushrooms to air and encourage fruiting. I’ve drawn red lines where I would usually slit my bags – you can do more or less, longer or shorter, you’ll find what works best for you. Smaller slits tend to produce multiple smaller clusters, whereas one large cut tends to produce one massive cluster. Use a sharp knife such as a boxcutter or carpet knife.

At that point, put your bag in its fruiting environment. This can either be a purpose-built chamber with a humidifier, outdoors if it’s cool but not cold and with high humidity, or even just on your kitchen counter, if you can remember to lightly mist it several times a day to maintain humidity.

After some time, sometimes days, sometimes a week, mushrooms will start to push through the slits. Let them grow out until the edges of the cap start to turn upwards, and then harvest and store them in your fridge. This is pretty much the ideal time to harvest them, if they’re oysters.


After harvesting, enjoy! Just leave the fruiting bag in whatever conditions you have it in, it should produce multiple harvests every week and a half or so, up to 3 or 4. Each harvest will generally be smaller than the last. When it’s stopped producing, or if it appears to be growing mold, you can break it up and put it in your compost to help break down woody matter, or put it in your garden with some wood chips and try to produce more mushrooms! You’ll know the block is done when it’s pulled away from the sides of the bag, appears dried up, and is quite a bit lighter in weight than when you started.

Many other growing methods exist as well – outdoor wood chip beds, plastic buckets, old coffee containers with holes drilled in them – options for any budget and commitment level. In this post we focused on using filter patch bags, made by a company called Unicorn, that allow the mycelium to breathe while still keeping contaminants out.

And that’s… not really it! We’ve skipped a LOT of important things, including hydration and sterilization of grains and substrate, but we’ll cover that in future posts – this is just meant to be a rough outline. Hopefully you’ve found it helpful, and stay tuned for more!

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