Greenery 101: Why Do Indoor Plants Collect Mildew Easily?

We have two answers to the question of why do indoor plants collect mildew. They are moisture and food sources, and you can read about them below.  


why do indoor plants collect mildew

What Is Mildew?

Mildew is an unwelcome yet familiar visitor in most households. It is a product of a humid and unkempt environment. 

Mainly, they develop because of water damage, as molds do. However, unlike molds, mildew prefers organic objects to victimize. 

Mold does not choose its victims. It can grow on stone, plastic, or plants, but mildew tends to be more often seen on plants. 

Another critical difference between the two types of fungi is that mold is darker than mildew. It can be green, greenish-black, or blue, depending on the type of mold you have. 

On the other hand, mildew’s color ranges from light yellow to white. 

There are two types of mildew, differentiated by texture: downy mildew and powdery mildew. To learn about what causes downy mildew, click on the linked article. 

As for the other mildew, you can easily read about how to treat powdery mildew on grass with this linked article. 


What Are The Reasons Why Indoor Plants Acquire Mildew?

Mildew spores are airborne, so it’s not surprising that they suddenly pop up out of nowhere in your home. They’re everywhere, and they need to find an excellent environment to settle on to live in. 

They especially like staying in organic environments. Unfortunately, that includes your plants. 

Plants are rich in organic debris, which serves as mildew’s food source. If you fail to remove fallen leaves from your plants’ pots, then you’re giving mildew spores its food source. 

There’s also the possibility of overwatering plants, which leads to heightened moisture. 

As you know, moisture is another prerequisite to mildew growth. If the environment’s humidity goes beyond 55°RH, then you’ll likely see mildew growing there in a few days. 

Ultimately, food sources and humidity are the main reasons why indoor plants grow mildew. Although, humidity does not just come in the form of overwatering. 

Indoor plants with uneven and narrow spacing will inhibit airflow among your line of indoor plants. This would then lead to trapped moisture, resulting in mildew growth. 


2 Different Types Of Mildew And The Plants They Victimize

The two different kinds of mildew generally damage different types of plants. 


Downy mildew

Downy mildew is detected on the underside of the leaves. Sometimes, they have a bluish tinge, and they grow in colonies.

When plants have downy mildew, tiny yellow spots show up on the top side of the leaves. When downy mildew infects your plant, the risk for having crispy leaves, insect attacks, and rotting fruits increases. 

Also, as the infected leaf dies, the mildew darkens to gray. 

The plants at risk of downy mildew infection are a wide range. Here are some of them that you may even keep as indoor plants:


1. Basil

Basil is vulnerable to downy mildew when grown in cool and moist conditions. However, you can always choose to plant basil later, when the weather is hot, to reduce the mildew risk. 


2. Ornamental plants

While ornamental plants make your home look lovely, they may also put it at risk since they are vulnerable to downy mildew. Considering how fast mildew spreads from one area to another, other indoor plants may also become infected. 

Downy mildew is more common among vegetation crops compared to indoor plants. Nonetheless, this type of mildew can still invade your home.  


Powdery mildew

Powdery mildew tends to thrive during spring when the temperatures reach 60 °F. Unlike downy mildew, powdery fungi do not have a wide range of hosts. 

It infects common indoor plants, but it is also common among outdoor plants. 

Powdery mildew infection leads to a decline in its host’s health. You will notice this as the leaves curl, twist, and become discolored. 

Sometimes, the white powdery build-up is not evident. Instead, you will notice imperfections and scorned patches. 

When powdery mildew infects flowers, they fail to open or develop abnormally.


How To Prevent Mildew From Growing On Indoor Plants


1. Avoid high humidity levels

This sounds like it’s out of your control, but it’s not, especially indoors. While the changing seasons may give rise to your home’s humidity level, you can invest in a dehumidifier to keep your household’s humidity within manageable levels. 


2. Keep it clean

You never know when a mildew spore can strike and infiltrate your indoor plants. Thus, you have to keep your environment clean so that it won’t have a food source. 

This includes removing organic debris from your plant pots. Naturally, this also involves inspecting your plants for possible infection and removing the mildew-contaminated parts before it spreads on the whole plant. 


3. All about spacing

Lastly, make sure that the spacing between your plants is even and that they have room to breathe. Narrow spaces lead to trapped moisture, which is terrible.

Moreover, airflow is necessary for plants as it helps dry their soil. 



All in all, the answer to why do indoor plants collect mildew is due to moisture and food source. There are different forms of moisture, which is why fungi can still sneak into your household despite it not having any water damage.

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