I am planning on indoor growing Shiitake mushrooms on wood pellets normally used for heating.

Is there a concern for toxic contamination through the pellets? After all the wood has been cut or shredded by blades, which might have leaked heavy metals and machine oils to the material.

Is there cause for concern? What substrate do commercial growing operations use? Can I somehow have the end product tested for certain contamination?

This is what the pellets look like:

enter image description here

There are no additives listed on the packaging and it says "environmentally friendly".


Growing mushrooms is not trivial; that is why until about 1980 only one was grown commercially in US ( Agaricus sp.). Shiitake grow on oak naturally and the documentary I have seen growing them commercially, they were grown on oak logs. So I think you have more of a challenge than a little white glue used to make the wood pellets ( probably from pine). Equipment used to make the pellets will be about 87 to 99% iron/steel. Such cutting tools are very unlikely to have any more than about 12% Cr. Processing equipment for FDA approved food processing have much higher alloy contents.

  • I don't understand your last sentence, do you mind reformulating? As for the glue I assume the mushroom can deal with it and break it down. But heavy metals can not be broken down and would end up in the fruiting body. – user1721135 Jan 1 '20 at 13:49
  • The FDA does not consider the possibility of metal ions potential release from appropriate process equipment to be any toxicity concern for food. – blacksmith37 Jan 2 '20 at 1:02

Virtually all shitake produced indoors by amateur growers are done so on those hardwood fuel pellets. You MUST make sure that you do not inadvertently get softwood pellets as these will not work well for shitake. I have experience using them for other mushrooms (oysters and lion's mane), but not shitake, and have read quite a bit about their use. While I've seen concern about toxicity from other substrates, I've yet to see a mention of a concern for toxins in hardwood fuel pellets.

As a side note, if this is your first time growing gourmet mushrooms, you might consider doing so without any nitrogen supplement the first time. This takes a little longer and the yields will not be as great. However by keeping the substrate nitrogen poor you will be reducing the chances of contamination - which is a serious concern in supplemented substrates.

Here is a discussion thread about using softwood pellets that might give some more info.

  • How do I find out if its hardwood or softwood? It doesn't say anything about the wood on the packaging. Its light in color. – user1721135 Jan 3 '20 at 23:21
  • Every bag I've purchased has indicated what it was made of. You could also look up the manufacturer/product online. – That Idiot Jan 5 '20 at 15:38
  • Its softwood apparently, and hardwood pellets are impossible to get. Will it grow at all on softwood? I already soaked them, should I toss it and look for hardwood? – user1721135 Jan 8 '20 at 9:22
  • If you have enough spawn to restart if this doesn't work, then I'd say give it a shot. Otherwise I'd wait until you can get a proven substrate.I found these online at Amazon (Camp Chef Smoker Grill Competition Blend Hardwood Pellets, 20 lbs (2 Pack)). If you order the 2 pack, it comes out to be about 2.5x the price of what I would pay locally, but its not like you're buying hundreds of bags. This would be enough pellets for a lot of grows. – That Idiot Jan 8 '20 at 12:31
  • I edited my answer to include a link to a relevant thread on Shroomery.org. It isn't my favorite site since it is very focused on illegal cultivation of psychadelic mushrooms, but there are some very knowledgeable people on there who grow gourmet mushrooms and they share great info. – That Idiot Jan 8 '20 at 12:41

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