I enjoy growing potted plants in my garden but found that a few of them are growing mold in the potting soil. I wanted to know why this was happening and what I can do about it.
Your potted plant or houseplant is growing mold due to overwatering. This means you’re watering the plant too often causing the soil to remain moist for a long time. This causes humid conditions that attract mold and fungal diseases to the potting soil.
Several other reasons may cause mold growth on your potted plant, and I’ve listed them below. I’ve also written steps you can take to get rid of this mold and prevent it from growing in the future.
Overwatering is a common issue beginning gardeners face because it feels better to give the plant a lot of water.
If the potted plant is overwatered, the potting soil remains moist for a long period. This creates a humid environment that is conducive for mold growth in the soil and plant.
If the potted plant is in a good setup, overwatering may not be an issue. But if the potting soil is poor and contains a lot of clay, it will keep moisture for a long period, causing overwatering.
The other reason for overwatering is because the pot or container lacks drainage holes. Or there are drainage holes, but they are blocked because of incorrect filler material used. Or clogging from the poor potting soil.
You need to give sufficient time for the potting soil to dry out between each watering. Otherwise, the humidity in the soil may lead to mold growth.
When it comes to mold on your houseplants’ soil, the most common cause is a combination of overwatering and cold temperatures. This is why the issue is a lot more common in winter and in the colder rooms of your home. When temperatures are low, the soil will take a lot longer to dry out, increasing the risk of mold and other issues such as root rot. – Joanna Turner, Fiddle & Thorn
Make sure there are sufficient drainage holes at the bottom of the pot. This helps drain out any excess water and prevent overwatering.
If you are using a saucer under the plant, throw away the water that collects after watering the plant.
It may be good if you can keep the potted plant at a height by placing stones or gravel underneath. This will help improve the drainage.
Check the moisture in the potting soil before watering it. Stick your finger 1-2 inches in the soil and check the tip of your finger for moisture. Only water the potting soil if the tip of your finger comes out dry.
Avoid letting the soil around your plants become too damp, and when you’ve removed the mold, mix some cinnamon into the soil. Finally, keep your plants somewhere open and breezy because mold will grow more readily in a stuffy, dark environment. – David Cohen, CEO, Flower Station
2. Too much fertilizer
Another issue beginner gardeners may create is adding a lot of fertilizer to the potting soil. Too much fertilizer, especially rich in nitrogen, will cause excessive foliage growth.
Dense foliage increases the chances of humidity. The nutrients, along with the favorable conditions, will invite mold to the potting soil and plant.
If you’re using organic fertilizer such as aged cow manure, it might be too old and contain mold spores. These will sprout when you use the manure in the potting soil and cause mold to grow there.
It’s best to add fertilizer as per the manufacturer’s instructions. You can plan the frequency and amount of fertilizer you need to use for the plants.
I would recommend only buying fertilizer sufficient for a few months. This prevents it from becoming stale and gathering mold that affects the soil.
Seal the fertilizer packet well after opening it. Keep it in a cool, dry place to avoid moist conditions that may cause mold to appear.
The most common cause of mold growth in potted plants is improper cultural practices. Cultural practices, with respect to gardening, refers to any physical method that is used to care for a plant such as watering, plant selection, plant location, soil medium, etc. but does not include fertilization, IPM, etc. In the case of mold growth it will likely be improper cultural practices around watering, soil type, location, or any combination of those. Simple changes in practice can be all it takes to reverse and prevent mold growth in potted plants. – James Houck, Founder & Proprietor – Ecostead, LLC
I asked several gardeners what they found was the cause of mold in their potted plants. 38% found that overwatering was the main cause of the issue. Below are the results of this survey.
3. Lack of sufficient sunlight
The most important factor for mold growth is humidity. And this occurs with ease if the potted plants lack sufficient sunlight.
The dense foliage and watering will leave moisture a lot longer on the plant. This causes humid conditions that are favorable for mold growth.
You need to ensure that the plants can get at least some sunlight that will help evaporate the moisture after watering the potted plants.
This can be a common issue with indoor plants or houseplants that are inside and rarely get the sunlight to dry out the excess moisture.
The simplest solution to prevent mold is to keep the potted plant in direct sunlight for a few hours. The mold prefers damp, humid conditions that go away with sufficient sunlight.
If you’re growing indoor plants or houseplants, you can move them outside for a few hours every day to keep mold away. If the potted plant is heavy, you can keep the pot on a moving tray so it’s easier to move around.
If you have a windowsill that gets plenty of sunlight, you can move the potted plant towards it.
This is often caused by over-watering, poor drainage, or insufficient light or air circulation. To get rid of the mold, it’s important to first make sure that the plant is receiving adequate air circulation. This can be achieved by increasing the amount of ventilation around the plant, such as opening up a window or using a fan to increase air circulation. If the plant is being over-watered, then it’s important to adjust the watering schedule and make sure that the pot has good drainage. To prevent mold from occurring in the future, it’s important to make sure that the plant is not being over-watered and that it’s receiving adequate light. – Tom Monson, Owner of Monson Lawn & Landscaping
4. Poor air circulation
Lack of good airflow among the plant’s foliage will slow down evaporation of moisture and cause humid conditions, leading to mold growth.
This may also happen because there are too many plants grown in one pot or the plants are growing too close to each other.
There should be sufficient growing space for the foliage and the size of the mature potted plant.
The major cause of fungus and mold is a humid condition in your potted plant. This happens when there is a lack of air circulation in the foliage.
You want to make sure the foliage is spaced apart to have good airflow. You can cut a few leaves if you feel this is a problem.
Make sure you’re not growing the potted plants very close to each other and give them sufficient space.
Another reason for the humidity is if there is water present in the foliage. Water only the potting soil and avoid splashing water on the leaves.
Mold can grow on potted plants for several reasons, including high humidity, poor air circulation, and overwatering. Remove all affected leaves, stems, and soil from the potted plant. This will help to prevent the spread of mold to other parts of the plant. Increase air circulation around the plant by placing it in a well-ventilated area or using a fan to create a gentle breeze. This will help to reduce humidity levels and prevent mold from growing. – Sholom Rosenbloom, Owner, Rosenbloom Pest Control
5. Poor potting soil
Poor potting soil may contain a lot of clay or stones, which will keep moisture for a lot longer and invite mold problems.
This may happen if you use a lot of garden soil for the potted plants that can contain clay and other materials. The garden soil may be too dense, that causes soil compaction and poor drainage.
The poor potting soil may also already contain the fungal spores that would become active once you use the soil and the conducive environment occurs.
If the potting soil contains impurities, the mold may find it attractive for nutrients and start developing. So make sure you buy high-quality and sterile potting soil.
Avoid using garden soil for your potted plants as it may already contain fungal spores. And if you really have to, make sure to sterilize the soil before use.
The simplest way to do this is to bake the soil in an oven at 180 degrees for at least an hour to get rid of any fungal spores and impurities.
6. Lack of drainage
The lack of drainage in the potting soil will encourage the humid conditions that we know lead to mold growth in the soil and plants.
This may happen because of several reasons, such as lack of sufficient drainage holes in the pot. Or there are drainage holes, but they are blocked because of the hardened soil or some gravel blocking them. Too much clay in the soil can also lead to poor drainage from the soil.
Sometimes there can be drainage problems, even with the drainage holes present when the pot is placed on a surface that blocks them. You can elevate the pots above the ground using pot feet, stones, or lids of plastic containers, being careful not to block the drainage holes.
I suggest checking the pot before you plant in it. Ensure there are enough drainage holes, or you’ll need to drill some yourself depending on the material of the pot. It’s easier to drill into plastic material than metal or ceramic.
You can place some dried leaves or coco coir at the bottom of the pot before adding the potting soil. This helps keep a separation layer between the drainage holes and the soil and encourages good drainage.
Every few weeks, inspect the drainage holes to see if they are blocked. You can use a narrow stick to dislodge the material if that’s the case.
Like I suggested earlier, it’s good to place the pot at an elevation so it can drain the excess water with ease. Use pot feet, stones, or broken terracotta pieces to elevate the pot.
If you place the plant pots in a tray, clear the collected water every day so it does not leach back into the soil. And you give the potting soil sufficient time to drain and dry out.
7. Unwanted debris in the pot
Leaves and debris of organic material will accumulate on the potting soil over time. The moisture from watering and the material will cause humid conditions suitable for mold growth.
It’s best to keep the potted plants clean from such leaves and debris as soon as possible. You can check the plants every day as part of your maintenance routine.
Mold prefers to grow in damp places with decaying foliage. So keep the potted plant and soil clean. Remove any dead or fallen leaves and flowers from the pot.
You can be proactive and deadhead the potted plants before the parts fall into the potting soil. Deadhead the flowers and leaves by picking those that are weak or dying.
Is mold on my potted plant dangerous?
The mold on the potted plant may harm the plant depending on the type of fungus that’s causing it. Some of them may cause the leaves to turn yellow or brown and fall off.
The mold may cause the leaves to not function as expected and they won’t be able to create nutrients with photosynthesis.
The spores of the mold could also be released into the air and cause allergies to humans and pets.
If you inhale a large quantity of the spores, it can irritate your respiratory system. This is especially a problem for people who are already suffering from ailments like asthma, COPD, or other breathing issues.
Some types of molds could produce mycotoxins that cause cancer, liver damage, and other health problems.
The mold that exists on potted plants has a specific name – powdery mildew. It is a fungal disease that can occur in almost any plant species. However, species such as African Violets and Begonias are particularly susceptible. The infection is characterized by a white mold that grows on the surface of the foliage of plants. Although it looks bad it is rarely fatal and can be treated. Powdery mildew is an air-borne disease. Infection usually starts with a small fungal spore that usually travels via the wind, however, it’s important to note that this could happen a long time before the plant enters your home or garden. – James Mayo, Exubia
How to get rid of mold on the potted plant?
1. Identify the type of mold
It’s good to identify the type of mold so you can check the impact and how to get rid of it. If the mold is black, it may be a type of fungus called “Botrytis.” Botrytis can cause plants to wilt and die.
If you think this might have happened with your plant, then remove all affected parts from around its base. Remove any dead leaves or flowers that are touching other vegetation for them not to spread spores.
2. Move the plant so it gets good sunlight
The easiest way to get rid of mold is to move the plant to a location that gets plenty of sunlight. The heat will dry up the mold and kill it.
If you’re growing potted plants indoors, it’s best to move them outside, at least for a few days till the problem goes away.
3. Wipe the mold off the plant
If the mold is a type that is just cosmetic, it will not affect the plant. It just looks bad on the foliage. You can use a cloth and wipe the mold from the leaves.
I would suggest soaking the cloth in a mixture of 1 part bleach and 9 parts water. This will act as a disinfectant and clean the mold. It will prevent any remaining spores from growing back again.
The easiest way to remove mold is to simply remove the layer of topsoil with the mold. You can also use hydrogen peroxide. Mix 12 tsp of 3% hydrogen peroxide with one gallon of water and pour it into a spray bottle. Spray the soil surface thoroughly. – Vladan Nikolic, Houseplant Expert, Mr. Houseplant
4. Cut off affected parts of the plant
If the mold is a type that is infecting the foliage and causing damage, you need to cut off the infected parts. The infected leaves and branches may have turned yellow, brown, or black because of the mold.
I suggest using a bypass pruner that is soaked in rubbing alcohol when you’re cutting the infected parts. This will prevent the spores from spreading to other parts or other plants.
5. Spray a natural fungicide on the plant
You can make a spray using materials like bleach, vinegar, hydrogen peroxide, or cinnamon. Mix 1 part of the material with 9 parts water and add it to a spraying bottle. Spray it on the affected foliage of the potted plant to get rid of the mold.
You can also use already available fungicide sprays that contain neem oil or horticultural oil. Wear gloves and a mask when spraying the fungicide on the plant.
There are a few different types of fungicides available on the market, so make sure to choose one that is safe to use on plants. Additionally, if you’re concerned about the safety of using a fungicide, you can also try using natural methods such as vinegar or baking soda to get rid of the mold. – Lina Cowley, Gardening Expert, Trimmed Roots
6. Repot the plant in fresh potting soil
If the mold has infected the potting soil as well, it’s best to get rid of it. You can transplant the plant into a fresh batch of potting soil.
You can reuse the pot after you have cleaned it up after removing the potting soil. Soak the pot in a mixture of 1 part bleach and 9 parts water that will help sterilize it. Keep it in this mixture for at least 1 hour.
Take the pot and rinse it well with water to remove all the mixture. Now you can add fresh, sterile potting soil to the pot and transplant the plant into this.