Why do I have mold on terracotta?
Mold readily grows in terracotta pots as the pots provide the perfect environment for it to grow. Terracotta absorbs moisture from the soil, the pores are moist almost all the time so they provide excellent conditions for the fungus to grow. If the pots are in a darker area, in high humidity and with little airflow, the fungus grows even faster. You will either see white fuzzy mold or black mold around the rim or on the sides of pots. Watering plants too frequently will also contribute, as will keeping plants in low light. With lower light, plants photosynthesize less, absorb less water from the soil, leaving the soil and the pot moist for longer periods of time.
How do i distinguish between mold and mineral deposits?
If you see fuzzy growth, you have mold. If you lightly scrape the mold with your finger, it will usually come off easily. Mineral deposits will not. Watch the Instagram video a few paragraphs below for a demonstration of the difference between mineral deposits and mold.
Can I leave the mold on terracotta? Is it harmful?
Mold on the outside of pots will not harm your plants. However, mold can be very harmful to human health, especially with prolonged exposure. Mold produces spores which can easily be inhaled. Some people are sensitive to mold and will experience stuffy nose, itchy eyes or skin, while people with allergies or asthma or compromised immune systems may experience more intense reactions. Make sure to remove all mold as soon as you notice it.
Cleaning method 1- using Hydrogen Peroxide – without taking the plant out
The first and easiest method to kill mold is by using hydrogen peroxide. Pour 3% hydrogen peroxide in a spray bottle and spray the outside of your pots, where the mold is located.
Let it sit for a few minutes. You will notice hydrogen peroxide sizzling as it’s interacting with the mold. Wash the outside of the pots with water to physically remove as much of the mold as you can. If needed, scrub the outside of terracotta with a brush. At the end, I like to spray a bit of hydrogen peroxide to the outside of the pots.
Check out this video of the whole cleaning procedure.
Make sure to not expose hydrogen peroxide to light as it will become ineffective and will not kill the mold.
Cleaning method 2- using bleach
A bleach solution is also an effective way to kill the mold. Mix one part bleach in 20 parts of water and put in a spray bottle. Since bleach is very strong and toxic, before applying I suggest taking the whole plant with the rootball out of the pot. Spray the outside surface of terracotta with bleach and scrub.
After removing the mold, soak the pot in clean water to remove the remaining bleach. Repeat 2-3 times, to make sure you removed all bleach. Let the pot air out for a few days, so the smell of bleach is completely gone before putting the plant back in. You can keep the plant in a temporary pot in the meantime.
Preventing Mold on Terracotta
A great way to prevent mildew from growing is to provide direct sun to the pots/plants that can handle it. Exposure to direct sun will kill the mold. Increased air circulation (you can use a fan) will also help. I also like to occasionally treat the outside of all my of terracotta pots with hydrogen peroxide.
This way I know I’ll be safe for a while.