The soil is "home depot cacti and succulent" brand.

this morning I noticed two little white mushrooms growing in the soil of one of my trichocereus cacti' s pot...

The soil did have chunks of manure and compost in it that I noticed when I was potting these when I was potting these cacti, though I'm still uncertain as to what this fungus is actually growing on...

Any ideas as to what kind of mushrooms these are?

And, are they a threat to the health of my cactus?

-eg

I tried to get some better pictures...

-eg

I was able to remove the mushrooms, as well as the underground chunk of mycellium they sprouted off of, though I did take a few more pictures first.

I stored the mushrooms after removing them.

They were tiny, about an inch tall tops, white gills, an annulus midway up the frail white stipe, white pileus which was less than an inch across which was ovate to conical.

I'm not sure if the mycellium was colonized on dead wood in the soil, on the soil itself, or on roots.

Leucocoprinus cepistipes mushrooms are common on gardens, compost, mulch, etc...and fit the description of my mushrooms fairly well...

Leucocoprinus birnbaumii is a likely candidate, these mushrooms are common in flower lots and green houses, all though this species tends to be more yellow to golden in color, though they can be white.

Leucocoprinus lilacinogranulosus fruits regularly in cactus pots in the University of Washington greenhouse, and shares similar description to the mushrooms seen in my cactus pot.

Lepiota sequoiarum, or some other lepiota mushrooms would have been other guesses, just as they are small white gilled mushrooms which commonly have an annulus...

Any way, here's another picture I took before removing the fungi...

-eg

Very cool! never seen that before

Cacti & mushroom, not so uncommon :

Ah, yes, the mushroom in that picture is Leucocoprinus birnbaumii, it was one of my guesses as to the ID of my mushroom, however these tend to be far more golden to brown than what I had.


Below were my guesses as to its ID:


-eg

Doesn´t this mean your soil is much to moist for the cactus?
If mycelium can grow in there maybe also other fungi that damage the roots?

However, when it forms mycorrhiza with the cactus that would be very nice.

Too much water for the cactus, most likely. So the fungi are growing out to help keep the soil dry. Whether this is adversely affecting the growth and health of the cacti, I'm not sure. I know a friend who had this recent outgrowth of mushrooms with his plants because the substrate was too moist but certainly not too late.

In this case it's been particularly hot out recently so I've been giving the cacti a little more water than usual, regardless, no more fungi have returned, and it was only those two carpophores that I saw...

After reviewing other fungi common in cacti pots I would not say they are necessarily bad, just something that can happen.

I wish I could ID my little white mushroom though.

-eg

Agreed...its just too much water. Your soil sounds a little dense. Mix in some pumice chunks and powder (or perolite) next time you repot. I put big hunks at the bottom of unglazed terra-cotta pots (with a drain hole) to ensure that the water can pass through and also eval through the terra-cotta.

You can under water, but that takes a long time to hurt the plant. Over watering (soggy soil for more than a day after watering) can cause rot pretty quick.

Mushrooms use a ton of water to fruit, so those little guys are probably answering the call to get that excess water out.

Good advice. I have a similar mix in soil currently, however I'm not certain that poor draining was the issue.

It had been incredibly hot, and I live at high altitude, it's very very dry, so I had been giving the cacti small amounts of additional water throughout the week, as well as misting them, I must have gone a little over board.

those were the only two carpophores I ever saw, I cut back water when I saw them and proceeded to remove them from the soil.

after browsing through some gardening forums I found this statement, which backs up my early speculations:



This is what I had figured, compost and manure in the soil already had spores which sprouted.

I wouldn't be alarmed by them, pretty common stuff, simply cut back the water.

after I noticed the carpophores I reduced water, removed and stored them and everything has been fine since.

I was actually fairly interested in these fungi guests, a nice surprise and an opportunity to research common fungi which appear in house plants, which I now have learned quite a bit about...it's as if nature suggests study topics by placing them in your life, great stuff.

-eg

A bit late on the uptake here, but I've had Leucocoprinus birnbaumii in one of my San Pedro pots before. There are some pictures buried somewhere in my file system, even. They absolutely do not appear to harm the cacti. I don't find the associated level of soil moisture to be harmful to the cacti either (during the warm season, at least). In fact, it's quite surprising how much watering my cacti have been able to handle!

I don't think I water enough...

I only water once a week, sometimes when it is really hot and dry I will give them some water, but it's always a small amount.

Nobody ever instructed me on how to care for these things, I have some college botany in my past, but as far as growing trichocereus cacti specifically, I am still learning, and mostly by trial and error. I had an interest in these cacti, so I acquired some samples, and have basically just been learning as I go.

-eg