A Guide to Fungus and Houseplants (What's Harmful and What's Not, and How To Fix It)

If you’re anything like me, when you see mold growing on something, it’s immediately being dunked into the trash can faster than you can blink. But if you see any kind of mold, mushroom, or other fungus growing on or around your precious houseplants, don’t freak out and trash it just yet; chances are, you can recover that healthy green sheen on those leaves with just a few environmental tweaks and a little TLC. And, crazy as it sounds, not all fungi are bad, either. Confused about which is which? Not to worry - we’ve put together this handy guide to determining what types of fungi you should and shouldn’t worry about, and what to do about each of them.

But first, some general Fungus Prevention Hacks:

Fungi, in general, thrive in humid, poorly ventilated areas and moist soil, though their temperature and humidity preferences vary. With that in mind, here are a few steps you can take to avoid dealing with most fungal houseplant problems:

1. Make sure your plant has plenty of air circulation around it. Move it a bit further away from other plants if they’re crammed tightly into a space, and ensure its spot is well-ventilated, but not too drafty. A low-speed oscillating fan can help.
2. Adjust your watering habits to avoid overwatering. A good rule of thumb is to check with your finger at least 2” down into the soil for moisture before watering. If it’s still moist, no need to water right now. For more watering tips, check out our essential guide to watering!
3. Water your houseplants in the morning rather than evening. It’s harder for soil to dry out at night, and the longer the soil sits in excess moisture, the easier it is for fungi to pop up.
4. Make sure your planter has proper drainage so that your plant doesn't get waterlogged. Our Wally Eco planters have small holes in the front panel that allow excess moisture to evaporate from the soil, which aerates and promotes root health at the same time. If your planter doesn't have drainage hole(s), keep your plant in a nursery pot inside it. 
5. Remove any dropped leaves or other dead plant parts as they appear to avoid rot and fungal growth.
6. If you’re particularly worried about fungal outbreaks, you can spray your plant with a homemade solution of baking soda and water, which is known to help prevent spores from taking hold by disrupting fungal cells’ ion balance. However, just make sure to dilute the solution thoroughly and test it on a leaf before spraying the whole plant, as too much baking soda can burn the leaves. Try 1 teaspoon of baking soda to 1 gallon of water.
7. In general, make sure you keep the specific needs of your species of houseplant in mind when choosing a location for it in your home. The healthier it is, the more resistant to problems (fungi or otherwise) it will be!

Mushrooms | the Good

Mushrooms growing out of houseplant soil can sometimes pop up in warm, humid rooms from spores in the soil mix, the air, or carried inside from clothes. These mushrooms are most commonly of the small yellow variety, and are completely harmless to the plant. In fact, they actually help break down the soil, so if you don’t mind their presence, you can just leave them alone! However, if you have pets or small children that might try to eat them, or you just don’t like the look of them, removing them is totally fine.

How to deal with it:

• Change the conditions around the plant to be less humid and warm, and water less often (but be careful not to harm your plant).
• Pull the mushrooms out by the base of their stems and throw them away. Be careful not to shake more spores out of their caps if they’ve matured to that point.
• Remove the top couple inches of the potting soil and throw it away. Replace it with new, sterilized potting soil.
• If mushrooms still pop up, it’s time to repot your entire plant. You’re trying to replace as much of the soil as possible without damaging its roots. Sterilize the pot first! Read our guide to repotting for more info.
• Still not working? Take your plant outside and drench the soil in fungicide, leaving it out to dry for a bit before bringing it back inside. You may have to do this multiple times if the problem persists.

Sooty Mold | the Bad

Sooty Mold is a black fungus that grows from clear honeydew secretions left by pests like scale, whitefly, and aphids. Sooty mold can take hold in dry, stagnant air. Because sooty mold covers leaf surfaces, blocking sunlight and interfering with photosynthesis, it can cause stunted growth and leaf drop in houseplants.

How to deal with it:

• To control sooty mold, treat the pest problem and the growth of the mold will stop. Look for the insects underneath leaves and in upper areas of growth. Specific treatment will depend on what kind of unwelcome guests your plant is harboring.
• General insect tip 1: Wash the leaves off with a hose (avoid high pressure water) or give your plant a shower to knock most insects off, though some may survive by clinging to tight corners.
• General insect tip 2: Spray the leaves with neem oil or a non-toxic pesticide outdoors. As the life cycle of the insects continues, you will most likely have to repeat this a few times until all the larva are gone. Make sure to get hard-to-reach places in the plant (crooks of stems, nodes, the underside of leaves).
• Once your pests are gone, clean off the leaves by wiping them down with a solution of dish soap and water - the sooty mold should come off with a little effort.

Powdery Mildew | the Bad

Powdery mildew can be caused by airborne fungal spores, and looks like a light dusting of flour or powdered sugar over leaves which will multiply and spread to the rest of the plant if left untreated. Powdery mildew likes dim conditions and stagnant air. This kind of mycelium fungus can deform a plant and cause it to become weak and drop leaves.

How to deal with it:

• Isolate the plant and cut out affected leaves. Move the plant to a spot with more air circulation and light.
• Take it outside and spray the plant with a houseplant fungicide, following the instructions on the label. A 3-in-1 insecticide/fungicide/miticide is the best bang for your buck, as it helps prevent other issues as well.
• After handling your plant, make sure to thoroughly wash your hands, tools, and clothing you were wearing to avoid spreading spores unintentionally to your other plants.
• Wiping off leaves with a soapy water solution regularly can help keep powdery mildew from coming back, and can help control insects, too.

White Mold | the... Okay

White mold growing on the surface of your plant’s soil is a harmless saprophytic fungus, but it may be a sign that your plant’s needs aren’t being met in terms of light, ventilation, and moisture. It won’t harm the plant directly, but may compete with the plant for nutrition, and you don’t exactly want to be breathing in mold, either.

How to deal with it:

• Wearing a breathing mask (or a scarf pulled up over your nose), use a trowel to scoop out and discard the top layer of soil, making sure to get all the mold in the process.
• If the mold is too extensive, you may want to repot the plant with new soil, sterilizing the pot beforehand. Check out our guide to repotting for help.
• Sprinkle a layer of ground cinnamon over the dry soil in an evenly distributed layer. Believe it or not, the compound that gives cinnamon its strong scent and flavor, cinnamaldehyde, is also a natural fungicide that can prevent the growth of mold!
• Adjust the plant’s environment in terms of air circulation, light, and watering to help prevent further fungus issues (see our fungus prevention hacks above).

Grey Mold (Botrytis) | the Bad

Grey Mold shows up as relatively large grayish-tan areas on leaves, stems, or flowers. The fungus has dusty, fuzzy grey spores that enjoy wet leaves and a combination of high humidity and cool temps. It usually affects older parts of the plant, entering through a broken stem or leaf, but it can quickly spread and cause the areas to collapse (which looks like wrinkly, drooping, shrinking tissue).

How to deal with it:

• Isolate the plant and cut out moldy parts of the plant, discarding carefully. Remember to wash your hands, tools and clothes to avoid bringing spores with you.
• Move your plant to a warmer room with less humidity, and keep air circulating around the plant.
• Dry the plant out completely and spray it with a fungicide outdoors on a cloudy day (following the instructions on the label). Once it’s dry again, bring it inside.
• Be diligent about removing dead stems, flowers and leaves as often as you can to get rid of the mold’s food source. When you trim back your plant or a stem is broken accidentally, dust the cuts with cinnamon or fungicidal powder to prevent any mold from taking hold there.

OSU Plant Clinic image, 2013

Stem, Crown, and Root Rot | the Ugly 

Stem, Crown and Root Rot is caused by fungal mycelia which lives indefinitely in soil, coexisting with houseplants. If you overwater your houseplant and air circulation isn’t enough to dry it out, especially in a cool environment, the fungus can suddenly and quickly multiply and take hold of the plant. If you see rot above the soil, you may also have root rot; read our essential guide to watering to learn how you can deal with root rot and improve your watering habits.

How to deal with it:

• If rot occurs above soil, cut out the rotted sections and use powdered fungicide on the cuts. If there’s too much rot to cut out to preserve the plant, take cuttings from healthy upper areas and try to propagate.
• Adjust your watering habits; water less, water in the morning, and always check the moisture of the soil 2” down before deciding it’s time to water. Avoid misting the plant, and don’t get water on the leaves or stem.
• It’s also a good idea to repot your plant and refresh it with new, dry soil as you do so, gently removing as much soil from the roots as possible without damaging them. Do not reuse the infected soil. Sterilize the pot first!
• For good measure, spray the plant and soil with houseplant fungicide, following the instructions on the label. Repeat every few days if necessary.
• If you’ve done all of the above and the plant continues to die, it might be time to cut your losses and start over; this is one fungus that is particularly hard to fight off!

Fungal Leaf Spots and Rust | the Bad

Spotted leaves can occur when spores in the air find a warm, wet leaf to stick to. The spore digs in and forms a small bump on the leaf which the leaf spot will then expand from. Caused by any number of species of fungi, fungal leaf spots can be yellow, tan, brown/reddish or black spots, sometimes with a yellow rim, in irregular circular shapes that can grow and merge to form larger lesions on leaves. If left untreated, fungal leaf spots can grow to cover the entire leaf and spread to stems and branches.

Rust is a kind of fungal leaf spot that looks a little different than most. When Rust spores take hold of a leaf, they will form red, bumpy spots on the surface of leaves and reddish-orange blisters on their undersides, and will cause leaves to drop and become warped. Though Rust is more common in outdoor gardens than houseplants, it’s good to keep an eye out for it.

How to deal with it:

• Isolate the plant and cut out affected leaves. Before throwing them away, first seal them in a ziplock bag to make sure the spores don’t spread.
• Improve air circulation around the plant and lower the humidity (if the plant won’t mind too much). For full plants, trimming some of the extra interior leaves can help the air circulate throughout the plant.
• Avoid misting the plant or getting water on leaves when you water it, and make sure it’s in a spot with a lot of bright, indirect light.
• Spray the plant all over with a houseplant fungicide solution outside on a cloudy day (following the instructions on the label). Make sure the plant dries out completely before bringing it back inside. You might have to do this several times if the problem persists.

We hope this handy guide has helped you foil any fungus you might find in your houseplants!