How To Kill Mold In Garden

Zach's writing ranges from matters of gardening, cooking, aquariums, and fish to more niche topics like coin collecting.

Struggling with moldy soil? Here's how to get rid of it without using chemicals.

White, Fuzzy Growth in Potted Plants

All is fine and dandy until you wake up one morning to discover that your favorite potted plant is growing fuzzy, white mold. Worried, you run to Google, type in "moldy potting soil," and end up here. That's a good thing too, because I've got the answers!

That stuff is probably a harmless saprophytic fungus. Below, you'll learn whether or not to be worried, how to remove the mold naturally and safely, and a few proactive steps you can take to ensure that it doesn't return. The process is quick and painless, for both you and your plants!

Is Moldy Soil Bad for Plants?

The quick answer is no, that white stuff growing in your potted plants will probably not harm them. Although you don't always see them, molds and fungi are present in every organic gardening mix. In fact, many organic gardeners believe that "living soil" is the ideal environment for growth. So it's a sign of life, although it might not be one you want to look at, since it's not exactly pretty.

On the other hand, a saprophytic fungus might also be a sign that your plant is not getting what it needs in terms of sunlight, air circulation, and moisture. The mold might also be competing for nutrition with your plant, so it is also a sign that you need to pay attention to.

How to Remove Mold From Soil

If there's mold growing under your houseplants, or in any container plant for that matter, here's what to do:

The first step is physical removal. Wearing a breathing mask, scrape off and discard the affected bits of soil.
Lightly dust the soil with ground cinnamon. Cinnamaldehyde, the stuff that gives regular cinnamon its flavor and scent, acts as the perfect natural fungicide and prevents mold growth. Try to get an even distribution and remember that it only takes a thin layer.
Do not water until the top two inches of soil are dry. For smaller containers (a gallon or smaller), wait until the top quarter inch has dried before returning to a water regimen. Use your finger to gauge moisture levels.

Potted plants are prone to mold. Impermeable plastic containers and pots without holes retain moisture.

What Else Can You Do?

Never let pots sit in saucers full of water for more than five minutes. Drain off excess moisture.
Place plants in sunlight or strong artificial light to help them dry.
If you see any mold, take the plant outside for a day to expose it to natural light and air. When you bring it back in, choose a new home for the plant in a spot that is slightly more sunny and breezy.
You might also consider transplanting to a larger pot full of fresh dirt. Make sure you choose a pot with plenty of drainage holes.

Is It Safe to Use a Bag of Old, Moldy Potting Soil?

Sometimes, you may not use all the potting soil at once; later, when you go to use some more, you discover that fuzzy white stuff has bloomed inside the bag. It might also be that you buy a new bag of potting soil, bring it home, and discover the same thing. The question is, can you still use that soil?

If you are transplanting, planting, or just replenishing dirt levels, the answer is yes. Before you use it, simply mix up the contents of the bag and work the white stuff back in with the dark. You might also add a little fresh compost. Cut the bag open and leave it outside, exposed to the sun and air, for a day or two, turning occasionally. You could also mix in some fresh compost.
On the other hand, if you're planning to sow seeds, you should not use that soil. Since the mold will compete with the seedlings for nutrients, it's best to give the new plants a fighting chance in some fresh dirt.

Is the White Stuff Growing in Your Potted Plants Dangerous to Humans?

If we see mold, most of us react by covering our mouths and running the other direction. But, although most mold-removal companies will try to persuade you otherwise, the mold in your potted plants is not particularly dangerous to humans.

On the other hand, if you are extremely sensitive to mold allergies, you might not want to take any risks. Some people have claimed that the spores trigger allergic reactions.

Outdoor container plants are less likely to grow mold, but it does happen. The plant likely needs less water and more sun and wind.

Photo By: Thomas Pix

How to Prevent Mold From Growing in Soil

Mold can never be totally eliminated. The truth is that mold spores are a regular part of soil and are normally harmless. The real threats to your plant are heat, humidity, and low ventilation. Under these conditions, mold spores grow into their adult fungi form and release even more spores. Indoor planters and container gardens are common hosts, as they retain more moisture. To prevent mold growth, follow the simple steps below:

Don't Overwater. Overwatering is the main cause of mold growth in container plants. Soil that is constantly moist is much more likely to harbor happy spores. Water only after a quarter of the pot's total soil volume has dried out. For example, if your plant's soil is 8" deep, don't water it until the top 2" have dried out. For most indoor plants, watering once a week should be sufficient.
Reduce Humidity & Increase Ventilation. Together, these two conditions create the stale environment in which mold thrives. By already not overwatering, you're also reducing the humidity, so to reduce moisture even further, place your plants in sunnier, well-ventilated areas or use a small fan to constantly push new air around the soil.

Final Word

Overall, mold in potting soil is very easy to treat. My one word of advice is to avoid the use of vinegar. Mold can survive the acidity, but your plant's roots may not! Cinnamon is a much safer and effective option.

Comments, questions, and suggestions are always appreciated!

Read More From Dengarden

This content is accurate and true to the best of the author's knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Alexandre on April 30, 2020:

Very helpful explanations and tips, thank you

Anna Rose Wilson on January 16, 2020:

Excellent advice, thank you!

Rhonda on January 08, 2020:

OMG!! THANK YOU SOOO MUCH! I LOVE ALL MY PLANTS AND DURUNG THE WINTER I BROUGHT A MAJORITY OF THEM INSIDE.. CHECKED ON THEM IN 3-5 DAYS AND TGE BEGAN TO HAVE MOLD IN DIRT!

IVE TRYED TO HAVE THE WINDOW OPEN, AFTER I WATER THEM, PUTTING THE OUTSIDE. GOID TO KNOW WHAT IM DOING WRONG!

Martha on November 08, 2019:

Thank you for your advice! I have an orange tree that developed white powdery stuff on the surface of the soil, when I brought it into the house for the Winter. I placed the orange tree in front of a large window facing West, in the bathroom. Perhaps the moisture in the bathroom is afecting the tree and caused the white powder on top of the soil.

I followed your advice. I wore a mask, removed the white powdery stuff with a plastic bag, as well as some of the soil and disposed of it. I then sprinkled a thin layer of cinnamon powder on top of the soil. I will also be moving the tree to a south window location, where it will be getting more sun light.The leaves are turning yellow, is there anything I can do to prevent the leaves from turning yellow? Thank you so much for your advice! Martha

Olivia on May 20, 2019:

Thank you for the informative information regarding how to treat mold.

Laura on December 30, 2018:

Very informative! Thank you..... I have some mold on the dirt of my indoor herb garden. Will the herbs be safe to consume?

Crystal on November 06, 2018:

I was worried that I would have to trash my umbrella plant. Because of this white furry stuff on the soil and stem. My only concern is will this effect my other plants?

Aurora on October 14, 2018:

Hello! my name is Aurora and I'm doing a science fair project on household items you can kill mold with, that won't harm your plant. I know you suggest to not use vinegar, but since it's a science fair project, I need to show it anyways. Thank you for making this post. It's helped me with my research!

Joyce on October 08, 2018:

Thank you for clear and exact directions and information. I feel confident that your suggestions will save my orchids.

Zach (author) from Colorado on October 03, 2018:

You're welcome! Hope the info helps out your fern!

Stephanie on September 29, 2018:

Wow! thanks for all that info! I have indoor fern plants and One is completely over growing and the other isn't looking so good. moldy and very skimpy. ( i will take it outside for natural sunlight and take it from there!

Zach (author) from Colorado on September 28, 2018:

Thank you!

Elizabeth on September 21, 2018:

Your information was and is awesome, since I did have a situation with mold. My husband said we had to replant them all. I was not to happy. MY friends has them now. Whether I will get any back is to be determined. Great post Thank You

Joshua Kempe on May 13, 2018:

I'm using Neem Oil and is Cinnamon better than Neem Oil? I got mold on my plants about a week ago and I made the mistake of not scooping out the existing mold and just sprayed it and the mold has not died yet... I'm really worried. I don't want moldy stuff in my apartment either and the neem oil really smells bad too. :(

Ellen Mae on March 29, 2018:

Thanks for the great tips!! Happy Spring

Fayehanson on December 31, 2017:

What is the yellow crusty stuff on my plants pot?

Patty pink on November 19, 2017:

Good to know these things!

Trish B on September 07, 2017:

Thank you, I know what i'm doing wrong now and how to correct it.

Many thanks

Isabelle on September 03, 2017:

Hello! Thank you for this helpful information! I have a question I hope you can help with. One of my potted plants got infested with mold, I planted two kinds of basil. One of the basil plants was basically dead while the other seems to be fine. I want to replant the basil that is ok with a new basil plant, new soil and all. Using your cinnamon trick on the basil that was with the infected soil, would it be safe to have in the new pot with the new basil plant? Or should I have two separate planters?

Alexi on August 24, 2017:

Not only did this solve my mold problem, but finally my "allergies" from the past few days make sense! I had forgotten about airborne mold spores... ._.

David on August 05, 2017:

thanks for the advice

Sandra on July 29, 2017:

Zach, I am glad I found your site. I will try the cinnamon treatment on my moldy plants. Thank you for the information!

Margaret Hicks on May 15, 2017:

Hello, I live in an apartment on the second floor and really don't think that I have any light coming in the window and don't want to take a chance and put it outside with the kids or someone may steal it, and I'm not sure what part of the day there would be any kind of sunlight on the balcony (if any). Is it possible I could put it under a desk lamp that uses a 15 watt lamp (maybe a florescent bulb as it is a long bulb, not sure).

Rusti on April 09, 2017:

Thank you! Easy to read and understand information, fast service. Loved this site!

Sabrina on April 08, 2017:

Thank you so much for all the information!

I got a whole planter with spinach full of furry white mold, I'm trying this!

Linda Matz on April 02, 2017:

I think I am going to really like this site!

Li on March 14, 2017:

Will try this

Thanks

Ryan on March 04, 2017:

My soil isnt moldy, but it has some kind of slimy substance on it. Any idea what it might be?

Michele on February 01, 2017:

Thanks for the tip about Cinnamon, I'll definitely try this. I have several Anthurium potted plants side by side and only one displayed wispy white strings on the soil, which I figured were spiders, so sprinkled heavily with Orange and Lemon peel (Spice World). 1 week later, the entire top is looking more like mold. The are in bright light but not sun which will burn the plant, I have a TheraPure increasing ventilation and they look extremely healthy with lots of blooms. Does this sound like mold? What else can I do?

Patricia Branagan Cannock staffs on December 20, 2016:

I had a new plant last week for a Christmas present( a Poinsettia) within days all the leaves dropped off, and the soil is already mouldy, does this mean than it was stored in the wrong conditions in the store. I will try your remedy. Thanks

Betsy Bowen on November 22, 2016:

Our house cleaner told us that there was white mold on our orchid plant, so we took it out side and threw all the old dirt and mold away. Gave it a good new supply of Miracle Grow, cleaned the pot, washed the roots of the plant and repotted it adding the ground cinammon. My housecleaner saw it today and suggested I ask Google what to do. What did we do wrong that made the mold show up again. We water it from the cold water at the kitchen sink as we do the other plants and they do not have the white mold. This plant was given to me by my best friend who passed away in June and I do so want to keep it safe and flowering. Thanks for your info.

Betsy Bowen at betsybow77@gmail.com

constance on November 13, 2016:

i keep my organic potting soil in a tub with a lid and now everytime i open it the whole top is covered in white fuzzy mold. this has never happened to me before. will the cinnamon work in this condition and should i dispose of soil or remove mold and keep?

Susan Johnson on October 25, 2016:

I love different ideas on how to take care of life with household products that are all natural I do have a question how often should we put the cinnamon in our plants once a month?

Susan Johnson on October 25, 2016:

Thank you so much I also knew this trip and my plants are growing beautifully now!!!! keep sharing!!!!

Ella on October 17, 2016:

This was very helpful! I am going to try the cinnamon trick, but another problem I am having is the mold is growing on the actual pot. Would this also be due to ventilation/lack of light? What kind of artificial light would be helpful?

David O on September 01, 2016:

Cinnamon did NOT work for me

Clara on August 03, 2016:

I put a fair amount of cinnamon on the earth of my large leaf plant was give to me when I lost my husband so don't know what it is called but it did have large cup size white flowers but I have transplanted it with the best earth and I watered it every two weeks now I am wondering if I can water over top of the Cimmon and how often should I water this plant ?

M on July 10, 2016:

Would irradiated cinnamon work?

Kathy on July 03, 2016:

Comment...I would like to know the cause of a powdery substance (from Flowers)

on my peace lily houseplant.mmIt also has a grayish film around the plant at base of potted

Plant. Are the two symptoms connected to the same problem? Also the lilies have brown

colored spots on them that have worsened and turned a darker brown with larger spots.

I have cut these flowers off along with the long stem. SOS here..I hate to lose this plant!!

I will try the Cinnamon treatment you have suggested andTHANKYOU!!

Sharinhall@yahoo.com on May 26, 2014:

What if you have brownish orange mold in your soil? It turns to powder wen u touch it. Will cinnamon work on this too?

Jaimie G. on November 17, 2013:

I had heard that using a splash of sprite in your house plants helped with the growth, because of the sugars and such! Well, since I have done this, I now have white furry mold growing on the plants and they are looking VERY unhealthy!!! HELP!!!!

Zach (author) from Colorado on March 24, 2013:

Virginia - Yes, you can sprinkle the cinnamon over the soil even if your plants have already been watered. Just plan on letting the soil dry out a bit before you water again.

Virginia on March 23, 2013:

I will be trying the cinnamon! I also want to know can you still sprinkle it even if you have already wartered your plants?

anne arsenault on February 03, 2013:

most of my plants have mold thanks I will try cinnamon hope it works

I never new what caused the mold thanks hope it works.

rbm on October 07, 2012:

Great tip, will definitely give this a try. Who knew that cinnamon could be used to get rid of mold! Pretty interesting.

Good hub, voted up and useful.

Zach (author) from Colorado on October 01, 2012:

Since the mold typically only affects the soil, the green onions should be just fine to eat.

Amanda on October 01, 2012:

Hello,

I've got furry white mold growing in my potted green onion's soil. Is it safe to still eat the onions after the mold is removed?? Thanks.

Jason Menayan from San Francisco on April 03, 2012:

I have this problem and ironically found your Hub via Google! I scraped the mold off, sprinkled a generous amount of cinnamon, and am waiting to see if it did the trick!

Zach (author) from Colorado on February 04, 2012:

@Elke - I'm not very familiar with Money Tree plants, nor is it easy to make a diagnosis without seeing the actual plant, but it seems to me you are correct. The white mold on the soil will most definitely affect new growth before the older established leaves. Along with the cinnamon, try to get a light/heat source that will dry the top layer of soil out a little quicker

Elke on February 03, 2012:

I'll try the cinnamon approach. I have a "Money Tree" plant. The new growth reaches a certain point, then withers and dies. The mature leaves seem unaffected so far, but I blame the white moldy film on top of the soil for the stunted growth of the baby leaves. Am I right?

Zach (author) from Colorado on January 26, 2012:

nifwlseirff - That you must! Cinnamon works great and can also be used in other areas of the garden too! If your plants show foliage signs of powdery mildew, cinnamon can be used as a spray to control it. I wish you the best of luck.

phoenix2327 - Hello again! The gardening bug is definitely running wild. As far as I can remember, Moss grows on soil because of moist and acidic conditions. I would recommend physically removing the moss and then sprinkling a little wood ash over the treated areas. The ash will make the pH swing up just enough to discourage future moss growth. Hope it helps you out.

Lissie Loomes - Glad I could show you something new! You'll be amazed at how well it works.

Lissie Loomes from Tasmania, Australia on January 25, 2012:

Thanks Joe for the cinnamon tip - hadn't heard it before but will certainly try it on my indoor garden when necessary.

Zulma Burgos-Dudgeon from United Kingdom on January 25, 2012:

You hubs are well timed as my mind is turning to a bit of gardening this weekend. I'm wondering if you might have any tips as to moss growing on top of the soil. Have shared this on Twitter and FB.

Kymberly Fergusson from Germany on January 25, 2012:

I must try cinnamon! I've been plagued with a little white 'film' on my potted plants' soil for months, which quickly grew back when the surface was scraped off. Thank you!