A couple of autumns back, I frequently went wild mushroom forraging, initially with my Basque father-in-law, who I think had been mushrooming pretty much all his life. He explained and showed how mushrooms would appear with the full moon. They would be plentiful and fresh for a few days, then gradually diminish. By the following waxing moon, any mushrooms found would be old and/or weak. There would be virtually none to find until the next full moon, when they'd suddenly be everywhere again.

Is there a scientific explanation for this?

To show that my father-in-law is not keeping a pet theory, there's plenty of talk associating mushrooms and mushroom harvesting with the full moon. For example:

While mushrooms are no doubt influenced by the Moon I'm willing to bet that individual species respond in different ways some flushing at the Full Moon others at the New and some contrarian species appearing in favored Quarters. A quick perusal of my notes and an Almanac hasn't revealed any particular pattern ... yet. But I'll keep looking. [Source]

Though here, mushroom picking must only happen at the time of the full moon, just as everybody also knows that root crops do best when planted in the waning half of the moon’s cycle. I raise a quizzical eyebrow. But no, I am assured: the gravitational pull of the moon brings more moisture to the surface of the soil and creates perfect conditions for plump porcini, in much the same way as the moon affects the tides. [Source]

The moon phase and sign actually do contribute markedly to environmental growing conditions. This refers mostly to gardening when starting vegetable/herb seeds in soil, but the moons positions does regulate available moisture and density within a medium. When the moon is waxing soil is expansive, and more moisture is available. [Source]

Pseudo-scientific explanations abound, some involving gravity/moisture, others involving moonlight, etc.

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    @userunknown the version I know is very simple: you go mushrooming with the full moon because there are more mushrooms. – Sklivvz Jan 9 '12 at 0:09
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    I have not encountered it. A rational hypothesis would be that it's partially true: the mushrooms do appear much more plentifully, but it's because the mushroom heads reflect moonlight and so are much more likely to be spotted. – MetaEd Jan 9 '12 at 16:27
  • @MetaEd you misunderstand the myth: you don't need to go at night :-) – Sklivvz Jan 11 '12 at 12:42

Chris, I too would go mushroom picking with my father in Sweden, and heard the same claim from him.

That said, this is more than likely a case of confirmation bias. Numerous questions have been asked here about the moon and its effect on things (I'll get to those afterwards). The biggest argument against this is would be to look at the biology of mushrooms. Since they are fungi, mushrooms do not need light for their lifecycle, since they don't contain chlorophyll.

Fungi are distinct from plants because they do not possess chlorophyll, the green pigment that allows plants to manufacture sugar from the sun's energy; they need to absorb their food from the environment in which they live.

As a matter of fact, there is a listing of mushroom species for cultivation in this PDF slideshow. In many cases, they explicitly state that no light is needed at all. Although, they may take phototropic cues to help in directionality of growth.

Now, the thing that will allow confirmation bias to creep into when you see mushrooms is that they have very rapid and cyclical life cycles. This paper for a specific white mushroom shows a 50-55 day cycle. Other mushrooms, such as the ones listed in the cultivation slideshow, show numerous time frames from 10 to 60 days.

In reading more about mushrooms, the key takeaway that I found in numerous pages is that biologists report (For instance, University of Wisconsin):

Very specific conditions of nutrition, humidity, carbon dioxide levels and temperature must be met for primordia to form.

Mushroom Life Cycle

Image from University of Northern Illinois Biology Department

Another trend in confirmation bias is that people may pick specific times to pick mushrooms based on those conditions of nutrition, humidity, carbon dioxide levels and temperature, such as after a rainy period, during specific months, etc. Add to those time phased events the natural human condition of being very susceptible to any type of confirmation bias, and there you have the claim.

As I said, there are oodles, and oodles of things people try to tie to moon phases, and in each case, there seems to be no actual correlation, only a perceived one.

Are more crimes committed during a full moon?

Do people with mental illnesses feel the effect more during the full moon?

Are more babies born during full moons?

Is the human menstrual cycle related to the lunar cycle?

In other words, there really doesn't seem to be a lot associated with a new or full moon.

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    "Since they are fungi, mushrooms do not react to light, since they don't contain chlorophyll." This is incorrect. Mushrooms and many other organisms without chlorophyll (including me) do respond to light. See, eg sciencedirect.com/science/article/pii/S1369527406001639 and books on mushroom cultivation by Paul Stamets – David LeBauer Jul 10 '15 at 4:16
  • @David You are correct, inelegant wording on my part. Could you suggest better wording as to why light (specifically moonlight) is not relevant to the mushroom life cycle? – Larian LeQuella Jul 11 '15 at 2:52
  • Hard to prove the absence of an effect, and unfortunately it is also hard to publish on effects that haven't been observed. I would say 'hasn't been observed / reported' instead of 'don't respond'. It should be straightforward to test for a 28 day cycle in a database of observations such as mushroomobserver.org. Still, it would be hard to say if such a signal were driven by mushroom response to the moon or by the response of mushroom hunters to the story. But it could be possible to account for this. Also note, the OP doesn't suggest the effect is caused by light - perhaps gravity. – David LeBauer Jul 11 '15 at 4:02
  • Sorry. Here is a decent study with one figure show no effect of the lunar cycle over 17 years of weekly samples, wsl.ch/dienstleistungen/inventare/pilzreservat/downloads/…. Their one figure is convincing, and they review a few other failures to find a relationship. – David LeBauer Jul 11 '15 at 4:13
  • @DavidLeBauer Dead link :( – frеdsbend Jul 20 at 18:55

Larian's answer suitably covers some logical issues with the claim, which is enough to perhaps comfort you in your skepticism, but it doesn't empirically answer the question for us.

It seems the association of the moon with mushrooms is ancient. Some ancient knowledge is derived from observation, but most of it is steeped in superstition and religious/occult dogma. The lunar/mushroom connection is no exception. A shallow delve into this topic quickly leads to pages discussing astrological signs, "mysterious" auras, and "ancient wisdom".

In terms of science, however, mushroom growth does not appear to be affected by the moon. In a study of 1715 mushroom harvest records, researchers in Switzerland found no relationship between harvest yields and lunar cycles.

Here we examine a total of 1715 dated mycological records, collected between 1990 and 2007 in five long-term observation plots in Switzerland to test for a possible relationship between lunar periodicity and mushroom yields. No such relationship was found, which means the claim that the moon phase influences mushroom production is based on myth.
Egli, S., F. Ayer, and M. Merlini. "More mushrooms under a full moon–myth or reality?." Sydowia 63.1 (2011): 23-33. - ResearchGate, abstract only
Full PDF Link

What mushrooms do require for successful growth is moisture, position (with regards to "food" mostly, as fungi are heterotrophic), soil integrity, and temperature, all of which may be more or less important depending on species. Light, from either the moon or the sun, does possibly contribute to growth direction, like virtually all plants, but does not affect growth robustness, as any simple "dark" growing experiment many of us have done as children shows.

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  • At the end here, I want to make clear that I understand plants grown in the dark do fail in robustness, but that is after the energy of the seed is spent. Such dark growing experiments are usually set up to show exactly this, that seeds contain energy and once spent the plant dies. With mushrooms, they can and often do grow in complete darkness, and in fact, the bulk of the fungi organism from which mushrooms grow is usually completely underground, as the mushroom is only the fruiting body for the organism. In analogous words, it's just the flower, not the plant. – frеdsbend Jul 20 at 19:18
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    As a follow up claim, I'd be very interested to know about the claim that the moon's gravity brings moisture to the soil surface, like tides to the shoreline. – frеdsbend Jul 20 at 20:04
  • It's also vaguely plausible that the soil could be loosened by the "tidal" effect. – Daniel R Hicks Jul 21 at 23:01
  • @DanielRHicks Yeah, I'm not skeptical there's no effects, but enough to predictably affect flora ... idk. If someone follows up on gardening, space, geology, etc SEs, please do link here. I might do it myself in the next few days, if I remember. – frеdsbend Jul 21 at 23:05

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