What are the little white fuzzy balls in my plant's soil? Eggs? Bugs? Mould? Fungus? Help!
First things first. Don't panic. Those white fuzzy balls that look like insect eggs, tiny cotton balls or white fuzz over the top of your soil, are most likely harmless to your plants, and not a sign of an imminent bug infestation (the fuzz or 'hairs' around the spheres is a good sign it's fungi not eggs). Not to be confused with Perlite of course (which looks like small, round, white balls, but won't be fuzzy).
What they are likely to be are a common type of fungi called saprophytic fungi. That's not a pathogenic or harmful fungi. Those little white, fuzzy balls are likely just fungal hyphae and the fuzziness around the spheres are the roots of the hyphae. Left to grow, you may end up with mushrooms next (I've had my fair share of cute yellow mushrooms pop up in my Peace Lilies in particular).
Let's take a look at what they are, where they come from, what they do, and what to do about it when you find mould, fungus or mushrooms in your indoor plants...
Is saprophytic fungi toxic or harmful?
The vast majority of fungi are saprophytic and feed on organic matter. They are usually harmless and in fact, beneficial. They can be a sign the conditions might not be ideal for your indoor plant, but shouldn't cause any harm to it in small numbers if caught early. It's only a small number of fungi, called pathogenic fungi, that are potentially harmful, causing things such as plant disease.
What does saprophytic fungi do?
Give fungi an ideal environment - moisture, nutrients and a confined space - and you might soon be growing mushrooms alongside your indoor plants. You might first notice this type of fungi as clusters of fuzzy white balls in the substrate or a white, fuzzy 'mould' on the surface of the soil. If you don't spot it at that stage, they might develop into mushrooms later (the fruiting body of the underground hyphae).
Saprophytic fungi feed on dead plant and animal remains. They break down organic matter into minerals and nutrients. When they fruit, you could find mushrooms or toadstools appearing in your indoor plants. In large numbers, the fungi can appear like 'mould' as a white covering over the soil surface. Left to its own devices, they can turn the substrate hydrophobic, where it repels water. Without water, plants can die, however like most plant hobbyists, it's likely you noticed it well before that's happened. Here's where it comes from, and what to do if you find it in your indoor plants or potting mix...
Where does saprophytic fungi come from?
Most potting mixes with organic matter can have fungi spores just hanging out, ready to spring into action in the right conditions. That can be before you even use your potting mix depending on how you store it, leading to finding white fuzzy eggs or mould, or even mushrooms growing in your bag of potting mix. You might have heard mushrooms are a sign of a healthy soil. That's because soil high in organic matter can make for a healthy, fertile medium for growing all sorts of things.
Common organic ingredients in a good potting mix, like bark, peat and moss, can contain saprophytic fungi. Their job is to break down and decompose the carbon compounds in the organic substrate in your potting mix. Yum (if you're fungi). What's good for fungi is often good for your plants too, as the more organic matter your soil includes the happier both your houseplants and fungi are likely to be.
In excess however, saprophytic fungi can reduce the water-holding capacity of the soil. Not so good for plants. This can turn soil hydrophobic over time. That's one reason when you go to water your freshly potted-up plant, that water just beads off and isn't able to be absorbed by the soil. Another reason it's advised to always buy only how much potting mix you need, and use it fresh (ideally within 30 days).
However, if the type of indoor plant you've discovered those white fuzzy spheres in, does NOT like to be kept wet, take those fungi as a sign something needs to change. The ideal conditions for fungi can lead to root rot for plants that don't like being too moist all the time.
Could they be insect eggs in your soil?
The first reason they're unlikely to be eggs is their size. Something pretty huge (in insect terms), would come out of an egg big enough to be easily seen by the human eye (like a large soil grub). Also, those fuzzy 'hairs' around the 'eggs' are another good sign, as they're what the roots of fungus look like.
How do you get rid of saprophytic fungi...
...if you find fungus in or on your plant's soil
Water less, provide better ventilation and better drainage (or all 3), and that's usually all that's needed for the fungi to naturally stop replicating and die off. More light can help also.
You can remove the fungi (while wearing a breathing mask). Carefully scoop those clusters of fuzzy balls out and into the bin or your compost heap. Don't worry if you can't get them all. If you're allergic to mould, best to glove and mask up, or ideally get someone else to remove it for you just in case. If the surface of the soil is very wet, you'll also want to help the plant dry off to avoid root rot. A warmer spot with more light will help soil dry out faster.
You can also sprinkle a thin layer of cinnamon over the surface of the soil to help prevent it growing back. Cinnamaldehyde is what gives cinnamon its flavour and scent, which is also a natural fungicide that helps prevent mould growth.
I've seen vinegar suggested also, but I would not personally use vinegar on plants or soil myself. Firstly, fungus and mould can survive the acid of vinegar, but your plant's roots might not.
...if your plant is in a cover pot
If your plant is in a nursery pot that normally lives inside a cover pot, temporarily remove it from the cover pot to increase airflow and ventilation and help it dry out faster. If your plant is in a pot without drainage, find a new pot. Not having drainage holes has far more pro's than con's, including a much higher risk of root rot and of root and leaf burn from the build-up of minerals over time from both water and fertiliser that can't escape.
Can you use potting mix or soil if it has fungus, mould or mushrooms growing in it?
In excess, saprophytic fungi can turn soil hydrophobic, so the substrate can no longer absorb water, which of course is bad news for your plant. In small amounts, you could still use the soil, however best to give it a good mix first to break up the white mould or fungi. You can also treat the soil to kill the mould and fungi, such as letting it dry out and exposing it to sunlight for a day or two.
However if you plant to use the soil for cuttings, seedlings or baby plants, I personally wouldn't use potting mix with mould or fungi, as it can quickly take over and compete with the baby plants for vital nutrients and water.
I much prefer to buy smaller bags of fresh potting mix to avoid that happening in the first place. It's also worth asking how long the potting mix has been in-store
Should you repot a plant with mould, mushrooms or fungus?
An airy, free-draining substrate - the type that most indoor plants love - also helps increase drainage, reduce water retention, and increase the amount of air in your soil, all things that help keep fungi at bay.
However unless there's other good reasons to repot your plant into a new potting mix, repotting should be a last resort. Repotting is like major surgery for a plant, and your attempt to kill the fungi by repotting could actually kill your plant. Try the other methods above first :)