The topic of mushrooms popping up in houseplant soil overnight is nuanced and there’s a lot to discuss, but if you’re thinking: ‘is my plant going to be ok? A mushroom’s turned up literally overnight and I’m panicking,’ rest assured:
- Your plant is more than likely totally fine
- The mushroom won’t harm your plant
- The level of toxicity is unknown, but they’re classified as medium – you’d need to eat large quantities for them to do any real damage, but even one will give you a bad stomach upset
- If kids/pets eat them, get them medical attention (though they’re unlikely to cause lasting harm)
- At best, your soil is very nutritious
- At worst, your soil is too damp and you need to either lay off the watering or add soil amendments to aid drainage.
If that’s answered all your questions, go about your day.
If you’re just super confused about how your houseplant went and found itself a little friend seemingly out of nowhere, read on!
What species are houseplant mushrooms, and where do they come from?
The most common houseplant mushroom is Leucocoprinus birnbaumii, which saw the booming tropical plant trade as a way of seeing the world.
You might also get Leucocoprinus cepistipes, which is bigger, wider and flatter than L. birnbaumii, and has a brown dot in the middle (like the one in the picture above). This one is less toxic.
Leucocoprinus birnbaumii is usually lemon yellow but can fade to white over time.
It was named in 1839 after a garden inspector named Birnbaum found it in a greenhouse, but was first described by English mycologist James Bolton the previous century. He called it Agaricus luteus because he hadn’t expected to find a tropical mushroom growing in a hothouse in Halifax, so assumed it was a species that grew closer to home.
Leucocoprinus birnbaumii are widely distributed across the world but were previously only found in the wild in the tropics and subtropics. They like warm weather, so whilst you can find them year-round, they're most likely to pop up in July and August (depending on where you live).
However, in the past 10 years, there have been reports of Leucocoprinus birnbaumii growing wild on forest floors in England.
You’re most likely to find houseplant mushrooms in plants that haven’t been repotted, but the spores can get into bags of potting soil, so they can turn up anytime.
How do mushrooms get into houseplants?
A single button mushroom can produce 1.36 billion spores. There are no reports on the spore count of Leucocoprinus birnbaumii, but even if it was a measly million, that’s plenty of spores to go around the growers.
The reason they just crop up at any time, even years after buying a plant, is that they appear, eat as much as they can (they feed on any nutrients they can find in the soil), and then disappear.
They won’t reappear until the surrounding conditions (i.e. it’s hot and humid) are met.
Are they the same mushroom species that grow in damp houses?
No. Leucocoprinus birnbaumii feed on the nutrients in the soil, and the spores are highly unlikely to germinate if it’s too cold and there’s no nutrient-rich soil around.
The mushrooms that appear in damp bathrooms are Peziza domiciliana. Don’t eat those either!
Let's all just agree not to eat mushrooms that weren't bought from a knowledgeable vendor or forager, ok?
Are houseplant mushrooms dangerous?
Yes and no.
I have an article here in the problems that houseplant mushrooms can cause.
Leucocoprinus birnbaumii are toxic to eat, but not touch.
They could be fatal IF (big if) you eat a lot of them. If a child or pet eats one or two, they’re unlikely to be in any real danger but they could end up with a seriously bad stomachache.
So whilst they’re not really harming your plant, I’d recommend that you pick them off and throw them away if you find them.
They’ve not had their ‘official’ toxicity measured, but it’s classified as medium.
The other type, Leucocoprinus cepistipes aren’t toxic, but they’re not tasty.
As for whether they do any harm to your plants, the answer is…not really. They’re saprotrophic fungi, which means they don’t want to harm the plant – they just want to eat the decaying matter around itt
They have the potential to be beneficial, as their mycelium (basically their root system) can enter a symbiotic relationship with your plant and they can provide extra root surface area in exchange for a few nutrients.
However, these relationships aren’t a given, and won’t happen between any fungi and any plant – most fungi have a specific plant that they, er, work with.
What definitely will happen is that your houseplant mushroom will consume nutrients from your plant’s soil. How much this will affect your plant will depend on how nutritious the soil is.
It’s unlikely to be a big issue, though.
Why do mushrooms grow in houseplants?
Because that’s where their spores ended up. it’s just chance.
However, the species of mushroom most commonly found in houseplants more than likely grows alongside your tropical houseplant’s wild counterpart.
Therefore, they’ll thrive in similar conditions – usually high levels of heat and humidity.
We’re creating a great environment for them.
You can’t do anything to attract mushrooms to your soil – the spores are already there. There are steps you can take to reduce the chance of the spores germinating.
What to do when mushrooms grow in your houseplants
I leave them – they don’t do a significant amount of harm and I don’t have any kids. My only pets are fish (there’s never really been an issue with them), and two house rabbits that have to be kept separated from my plants for *ahem* other reasons.
Just leave them, they’ll likely disappear in a few days.
If you need rid of them, you can just remove them, but they’re difficult to prevent. They’re not toxic to touch, but wash your hands afterwards, just in case.
There’s not really much point in repotting your plants. Unless you sterilise your soil you’re unlikely to be able to 100% ensure they won’t turn up again.
Sterilising soil to get rid of houseplant pests has become very popular over the years, and…it’s not the way.
Sure, it can get rid of the bad bugs, but beneficial bugs are…beneficial (I’m such a good writer).
Also, the second you fertilise your plants, you’re back to square one.
You could also try a top dressing to deter them – sand or gravel would probably hinder their growth.
Are mushrooms in houseplants a sign of overwatering?
Mushrooms in houseplants can be a sign that there’s too much moisture in your soil because Leucocoprinus birnbaumii need damp soil and high humidity to germinate.
When you see a mushroom in your houseplant pot, don’t assume you’ve overwatered, but do take the time to check the roots and the soil – just in case.
Houseplants that like staying moist, like Calathea and peace lilies, are more likely to get mushrooms than other plants, because their soil is likely to retain more water than, say, an aloe’s would.
There are some plants that shouldn't be staying moist enough to produce mushrooms in the soil. For example, snake plants, cacti, aloe, and jade plants should be in a very well-draining soil mix that's unlikely to provide a good home for a houseplant mushroom. Epiphytic orchids like Phalaenopsis definitely shouldn't be producing mushrooms, because an appropriate potting mix is unlikely to provide them with enough nutrients or moisture. Should you find a mushroom in one of those plants, check the roots and consider either putting it in a better potting mix or moving it to a warmer spot so the soil can dry out quickly.
Can you keep mushrooms as houseplants?
Technically no, because they’re not plants. But also you can buy mushroom growing kits online that are a lot of fun.
Are mushrooms a sign of good soil?
A Leucocoprinus birnbaumii popping up in your potted plant isn’t a good or a bad thing.
It’s…just something that happened.
They’re a sign that your soil is nutritious, damp and warm enough to support a Leucocoprinus birnbaumii.
If your plant lives in a similar niche to Leucocoprinus birnbaumii in the wild, then it could be a good thing. If it doesn’t it might be a bad thing…but it might not.
Mushrooms *tend* to grow in low-lit, damp environments with less than stellar airflow. That's not a great environment for many houseplants. I've had them pop up in my Monstera Dubia that's got good airflow and is in bright light. Life, uh, finds a way.
The perfect amount of worm castings in your soil could prompt a mushroom to grow and your soil would be healthy. But also if you repot your snake plant in 50% compost and 50% houseplant soil you bought from the garden centre, a mushroom could pop up, but that’s not a great soil mix for your plant.
In short, don’t automatically assume a mushroom = healthy soil
OR
a mushroom = unhealthy soil.
Are mushrooms a sign of mould?
Mushrooms and mold are all species of fungi, but they’re not the same, and mushrooms aren’t necessarily a sign of mold.
There are anywhere between one and five million species of fungi, for reference.
Houseplant mold isn't usually harmful to the plant, but can be a sign that the top of the dry isn't drying out fast enough. It's super common in early spring when the plant starts growing but it's still not properly warm, and doesn't usually indicate an issue.
There’s also that stuff that looks like white balls which commonly grows on soil and is a mostly harmless saprophytic fungi that won’t harm you or your plant but might nick nutrients from the soil.
Leucocoprinus birnbaumii isn’t a sign of mould, and is also a saprophytic* fungi.
*it means they eat decaying matter.
Can mushrooms be beneficial to houseplants?
Leucocoprinus birnbaumii can be beneficial to houseplants because they absorb a lot of carbon from houseplant soil. Most houseplant potting mixes contain varying amounts of peat moss and/or bark, meaning that the substrate could be 20% carbon. Considering most houseplants naturally grow in places where soil is about 2% carbon…it’s a bit overkill.
Whilst not having mushrooms doesn’t cause carbon poisoning or similar, the presence of Leucocoprinus birnbaumii can reduce carbon levels and your plant might be very slightly healthier.
There are beneficial fungi you can add to your houseplants though, and a lot of houseplant people swear by adding them to the soil.
What beneficial fungi can we add to our houseplants?
There are compelling reasons both for and against adding mycorrhizal fungi to your houseplant soil, but personally, I don’t think the products are quite there yet.
A mycorrhiza is a symbiotic relationship between a fungus and a plant. So your houseplant and your mushroom could have a mycorrhizal.
However, as I mentioned earlier, fungi won’t just strike up a deal with any plant, and different strains are pickier than others.
I’m pretty sure, for example, Leucocoprinus birnbaumii doesn’t do anything significant for your plants in terms of helping out the roots – whilst there’s no actual information on it, the fact you can’t buy them speaks volumes.
But you can buy strains of mycorrhizal fungi that have been specially developed to help houseplants.
The benefits of adding mycorrhizal fungi to houseplant soil
So, what do these mycorrhizal fungi producers promise?
- Improved water and nutrient uptake
Mycorrhizal fungi attach to plant roots to effectively increase the amount of roots. The fungi will take carbohydrates from the plant in exchange, but both parties get a pretty sweet deal.
In terms of houseplants, this could mean that you could get away with using bigger pots without risking root rot, because the mycelium would also be absorbing water from the soil.
- More abundant flowers and better crop yields
This is a result of the improved root system so it’s more of an extension of improving water and nutrient uptake.
Whilst adding mycorrhizal fungi to houseplant soil can maximise the effectiveness of roots it won’t increase levels of moisture or nutrients in the pot.
- Plants need less fertiliser and are more drought-resistant
I’m sceptical.
This is true in a plant’s natural habitat. Mycorrhizal fungi extend their mycelium (which is works like a root system) and attach to the plant’s roots so the roots can travel further down to get water and nutrients.
This does not hold up in a potted plant. The roots aren’t gonna come out of the bottom of the pot and grow over towards the sink.
- Can help plants overcome replant disorder
Not really something houseplant people need to worry about BUT if you grow ornamental roses it could be something to look into.
Things to consider before adding mycorrhizal fungi to houseplant soil
1 – Ectomycorrhizae vs. endomycorrhizae
Mycorrhizal fungi can have two different types of relationships with plants – ectomycorrhizae or endomycorrhizae.
Ectomycorrhizae don’t penetrate deep into the plant’s cortical cells. Endomycorrhizae do. Guess which one is the most efficient?
When you buy mycorrhizal fungi, they don’t tell you which strain you’re getting, and whether it’s endo or ectomycorrhizal, but most soil scientists are pretty certain they’re ectomycorrhizal, and therefore won’t forge that string of a relationship with the plant.
2 – You don’t know what strain you’re getting
You can’t just stick a mycorrhizal fungi and a plant together and have them form a bond that leads to a mutually beneficial relationship.
There are thought to be 50,000 species of mycorrhizal fungi out there. Chanterelles are one, as are puffballs.
3 – Mycorrhizal fungi are delicate
If you add mycorrhizal fungi to your soil, you have to be careful about:
- letting your soil get too hot
- Using pesticides
- Using fertilisers – mycorrhizal fungi can increase the absorption of nutrients (it increases uptake of phosphorus by 80%) so you should still fertilise, but they can be sensitive to overfertilising so read the instructions and check that it’s safe to use in conjunction with MF.
- Using fungicides
- Or any additive that could potentially kill the mycorrhizal fungi. I tried to look up the impact of silicon on MF but scientists are still fighting about it.
- Letting your soil dry out too much
The fact that mycorrhizal fungi will die if they get too hot is reason enough for me not to buy them. Maybe in winter, but that’s not really when I need an extra root system.
If they’re in a delivery van on a hot day, they could be dead before they even reach me. We also have no idea how they’ve been stored – especially if you’re getting from, for example, Amazon.
They can also die if left too long without water so they’d be no good for me. Whilst it could lead to improved uptake of water, we don’t have infinite water in potted plants. Soooo I’d have to water more often. No ta.
They come in granular form, so it’s not like you’re gonna open it, see a lot of perished mushrooms, and send it back. You won’t know.
I also couldn’t find information on what they add to the soil, so they could add in fertilisers or root boosters to ensure you notice a difference when you use it.
Let me know of your experience with beneficial fungus, or mushrooms in your houseplants – I like to hear everyone’s experiences.
Read this article for more information on mycorrhizal fungi.
Final thoughts
Mushrooms popping on your houseplant is pretty common and isn’t necessarily a sign that there’s anything wrong with your houseplant. They can be toxic so remove them if you have pets and kids, but unless they eat dozens they’re unlikely to get anything worse than a bad stomachache.
Mushrooms can form symbiotic relationships with plants in their natural environment by essentially attaching to each other’s roots. Plants provide the fungi with carbon dioxide, and the fungi improve the plant’s ability to absorb water and nutrients through its roots.
You can buy mycorrhizal fungi to add to houseplant soil but the jury’s out on how effective it is.
