Mould On My Soil! What Is It, Why Is It There & What Do I Do?
Updated: Jun 9, 2021
You’re a small-space gardener with a few potted plants. You love your plants - who doesn’t? - and you want to see them thrive.
There you are, minding your own business when BLAM! - you notice that there is some mould growing on the surface of your soil.
Next step is, obviously, googling what is wrong with your tiny garden.
Well, first thing to keep in mind: don’t panic! The mould you see growing there is not dangerous, not usually allergenic, and is actually a good thing for your plants and soil. If you require more convincing, read on!
Note: Experiencing other troubleshooting issues with your plants? Check out Epic Gardening's Plant Problems for some top tips!
What Type of Mould Is It?
Does the mould on the surface of your potted plant’s soil look something like this:
If so, then this is almost certainly something called saprophytic fungi (mould). Saprophytic means: an organism which consumes decaying organic matter. When you see mould in your potted plants, this is essentially your plants going “wow, this soil is LIT!” Saprophytic fungi are known as “litter transformers”. By eating dead organic material, they literally change the chemical composition of that material into something valuable for the soil. Saprophytic microbes are therefore very important to composting, as they break down the organic material added to compost piles to turn it into rich soil. They essentially eat garbage and poop out gold. Note: Not literal gold. Lol. Compost fungi that result in mould are most often actinomycetes. Now, we’re not expecting you to remember that fancy word, but just know that these guys are naturally occurring in soil and that their presence is a GOOD THING.
Why Is There Mould On My Soil?
We’ve learned that the fungi which results in this type of mould (or “fruiting bodies” of fungi) is naturally occurring. But not all soils have visible proof that these fungi are indeed present. Why, then, are you seeing mould? Indoor plants are unfortunately (or fortunately, depending on whether you’re looking at this scenario from the soil’s perspective) nearly a perfect environment for saprophytic fungi to develop fruiting bodies - mold. The soil is closed-in, regularly dampened, and is not usually turned or aerated by either bugs, animals or gardeners. 1. Not Enough Aeration There could be multiple reasons for seeing mould. Actinomycetes thrive in anaerobic (no air) conditions. If you’re seeing white mould on your soil, this could mean that there is an excess of anaerobic conditions - too little aeration - and actinomycetes are taking advantage. 2. Not Enough Sunlight Not allowing your indoor plants to bask in the sun will limit the nutrients made available to these plants through photosynthesis. Insufficient natural light will also encourage the dark-and-damp conditions that mould loves so much. 3. Poor Drainage/Over-Watering The same could be said for poor drainage in your soil. Fungi generate spores which float on any small air current and land nearby (for the most part). However, if the environment is not comfortable for them - lacking sufficient moisture - they will not propagate and develop into mould. 4. Organic Fertilizers If you add an organic fertilizer to your soil just before planting or after you’ve already planted, you are increasing the risk of seeing that white mould on the top of your soil. Fertilizer produced by an electric composter, or a material such as PittMoss, is a regular suspect for feeding the existing bacteria in your soil. Because the powerful biomatter introduced into your soil is still in the process of decomposing, it is providing all the necessary nutrients for these bacteria (and your soil) to thrive. Now, remember, this is a GOOD THING. You absolutely want to encourage the health and diversity of these bacteria and fungi. However, just know that mould is often a symptom of this natural and positive phenomenon. Seeing mould from actinomycetes in your compost is fairly normal. Once the compost has broken down into soil, it has been digested by fungi to such an extent that these bacteria are unlikely to produce mould after being added to your soil. However, it’s not impossible. Because electric composters essentially reverse and speed up the process of traditional composting, the by-product (or fertilizer) produced by the compost machines requires a curing period in the soil before being equally broken down. So, to reiterate: if you see white mould on the top of your garden/potted plant soil - this is just the next step of the natural decomposition process going on in your soil as the organic fertilizer releases its nutrients to the soil and your plant roots. What Should I Do About the Mold? Well, that’s entirely up to you. Do you care if there’s a bit of white fuzz on top of your soil? If not, then go ahead and let Mother Nature get on with it. Once the biomatter is completely decomposed in your soil, that mould will eventually disappear! But if it bothers you, or you’re concerned about the spores potentially irritating an existing asthma or bronchial sensitivity, then fixing the issue is fairly straightforward. 1. Try re-potting your plants: Your plants and soil might be a little claustrophobic in such close quarters. To give them more space and a better chance at soil aeration (decreasing anaerobic conditions), try giving them a larger environment and potting with fresh soil. 2. Give them more sunlight: Nothing scares mould and mould-producing conditions better than good old fashioned Vitamin D. Put your plant closer to a window during peak sunlight hours and let their soil conditions dry out and warm up a bit. Note: This may not be a good idea for some plants. Certain species require indirect or even very little sunlight and may start to wither, dry out or die if given too much sunlight. 3. Add better drainage: Even if you’re following the proper care instructions for your plant babies, the conditions might still be too wet due to insufficient drainage. Make sure that your flower pots have holes in the bottom to allow water to seep out, and a dish for the excess water to collect so that your plant can collect it as needed throughout the day/week. Adding rocks to the base of a flower pot before adding earth and seeds/plants can also help with drainage, and supporting the root structure (giving the plant roots something to which they can cling). 4. Mix in organic fertilizer with proper ratio: Are you sure that you mixed your fertilizer in correctly? It could be that there is either too high a concentration of fertilizer in one area (like the top of the soil, for example) and that this is inviting mould to grow. The ideal ratio for most organic fertilizers can vary, though we do recommend a minimum of 1 part fertilizer to 10 parts soil. This will spread out the fertilizer particles so that they can feed the bacteria in the soil without giving them too much, too soon and inviting a nitrogen and/or nutrient glut. Always make sure to mix the fertilizer in with the soil thoroughly. Adding fertilizer is best done when you’re re-potting an existing plant with fresh soil, or starting a new garden with fresh soil. Mixing in by-product properly and at the correct ratio can be tricky with existing potted plants, as there is so little room to go around. 5. Just wipe it away! Yup, that easy. Instructions:
Wet a paper napkin
Use the napkin to collect all visible mould particles
Throw away in trash or compost bin
There you are! Problem solved! Note: If you are concerned about any irritation to existing bronchial conditions or allergies, you might feel more comfortable if you performed this task in an open-air location, or even step outside with your plant to clean things up. You can also wear a construction mask if you’re super-duper concerned. Safety first!