I have some mycelium growing on cardboard but I am wondering what is in the cardboard other than carbon, oxygen and hydrogen that the fungus can use. How is it meeting it's need for nitrogen and other elements ?

2 Answers 2


Oyster mushrooms (and others) can grow and fruit on cardboard alone, or dried wood chips or straw alone - as long as their requirements for water, light, temperature, and ventilation are met.

The effect of nitrogen on mushroom production is best considered with the metric called Biological Efficiency (BE), which is the ratio of the weight of mushrooms produced to the dry weight of the substrate used.

So where you may get 7 lbs. of mushrooms from a 10 lb. (dry) bag of un-supplemented straw or cardboard (a 70% BE), you could get 11 lbs. from a 10 lb. bag of nitrogen supplemented straw (110% BE).

The ability of oyster mushrooms to grow and produce quite well on un-supplemented substrates makes them great for beginners because very few other organisms can compete with them. Most bacteria and molds need more nitrogen to grow quickly.

However when you start looking to increase BE, supplementing with nitrogen (from alfalfa, bran, fertilizer, even urine) is the most effective way to do so. The problem is that this higher nitrogen substrate is now also a great environment for the common mushroom contaminants. Extra steps and care area needed to grow mushrooms in supplemented media.

Other common "additives" are gypsum, limestone, and sometimes hydrated lime. These provide micronutrients and can stabilize pH. The lime can be used to pasteurize the bulk substrate prior to inoculation.

  • Great, thanks. Does that mean they actually grow without nitrogen (and other elements), or they get it from the air, or does even cardboard have it ? For a start DNA has to have phosphorous and nitrogen so not much will happen unless mushy has those too. I suppose they are in tree derived products in trace amounts ? Mar 21, 2018 at 15:46
  • They can get by on what's in the substrate. I do not believe they can fix nitrogen at all, and I don't know of phosphorous being airborne other than in polluted rain or eolian sediments - neither of which would be a factor in indoor cultivation.
    – That Idiot
    Mar 21, 2018 at 15:54
  • Yeah I'll have to look at getting some gypsum and lime then. I also read that molasses helps. Mar 21, 2018 at 17:25
  • Careful with the lime. If using for pasteurization of substrate, you need to make sure it is a low magnesium hydrated lime rather than some other limes you can buy. Also make sure you use caution not to burn your skin, lungs or clothes as hydrated lime is incredibly caustic and powdery.
    – That Idiot
    Mar 22, 2018 at 11:17

Pleurotus genus is essentially cellulolytic (Silva et al., 2012a), however, there are fungi that grow on substrates with low nitrogen content in the range from 0.03% to 1.0% (Machado et al., 2015). Ortega et al. (1992), in their studies with Pleurotus spp. cultured on bagasse supplemented, described a nitrogen increase in mushrooms related to the amount present in the initial substrate plus the nitrogen amount present in the inoculum, indicating a possible fixation of this element by mushrooms. Sturion and Oetterer (1995) also observed a nitrogen increase in the residual substrate, which ranged from 4% to 37% in the cultivation of Pleurotus spp. on different substrates, suggesting the possibility that this genus fixes nitrogen, or the presence of fixing bacteria associated with the mushroom.


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    Nice, thanks. Don't forget, god gave nematodes the task of bringing nitrogen to the oyster mushrooms. youtu.be/6LNPxOKESfk Mar 22, 2018 at 10:46
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    So, given that Our Lord in His Wisdom sorted the oyster mushrooms out with nematodes, might it be a good idea to throw some soil into substrate if it looks like it's properly colonised already ? Obviously it might lead to contamination growth, but in an established grow that would be less risky wouldn't it ? Oyster mushrooms have lived with dirt for millions of years, after all. Mar 22, 2018 at 10:54
  • I've seen videos of oyster mushrooms growing in mulch in gardens, but I've never encountered them in direct contact with soil in the wild and unlike some cultivated mushrooms that require soil contact, no commercial production that I'm familiar with includes soil addition or contact.
    – That Idiot
    Mar 22, 2018 at 11:15
  • Chuck in a few dead insects? Mar 22, 2018 at 12:17
  • Since it grows on low nitrogen substrates I guess it's not surprising that it might be able to fix atmospheric nitrogen Mar 23, 2018 at 4:37

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