What Does Mold Need to Survive?

Mold is a common theme here on RepairSprout. So many Americans experience mold in their households each year (around 11 million to be exact), yet so few of them understand anything related to mold.

Many are unaware of just how dangerous mold can be and the potential property damage it can cause if left untreated for a long enough timeframe. Most people also don’t understand how does mold even grow. 

In today’s blog, we’ll discuss what does mold need to survive and other things you should know regarding mold growth. 

This one will be quick, so let’s get right into it!

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What is Mold?

Mold is a fungus composed of so-called mold colonies. These colonies have a fuzzy or slimy appearance, and they are what we consider mold. So, basically, what you call mold is actually a group of these colonies.

Mold colonies form when mold spores land on a wet organic surface and start growing.

Now, mold spores are tiny reproductive cells produced by mold fungi as part of their natural life cycle. They are so small that they are not visible to the naked eye, typically ranging in size from 1 to 30 microns.

These spores are airborne and are present in our environment at all times, both indoors and outdoors.

There are over 100,000 species of mold, but homeowners typically deal with some of these:

  • Aspergillus
  • Cladosporium
  • Stachybotrys chartarum
  • Penicillium
  • Alternaria

These can be in varying colors, including black, brown, or green.

So, how does mold actually form? We’ll now get to that.

How Does Mold Grow?

Mold begins its life cycle as tiny, lightweight mold spores. As we’ve said before, these spores are omnipresent in the air, constantly floating around, waiting for the right conditions to settle and grow.

Once a spore lands on a surface, it begins to germinate. This basically means that the mold spore starts to absorb water around it and swell.

This triggers the activation of the spore, initiating the growth of thread-like structures called hyphae.

These hyphae then extend and form a network known as mycelium, which is the main body of the mold. The mycelium is responsible for extracting nutrients from the surrounding environment, allowing the mold colony to expand.

We’ll later touch on what these nutrients actually are and what conditions are best suited for mold. But know that the more of your stuff mold eats, the more nutrients it will consume and use as energy. 

The more it does this, the more it will grow. And the cycle continues until all of the mold has been removed. These mold bodies will also continue producing new spores that will spread throughout your house.

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Conditions Mold Needs for Growth

Environmental Conditions

Let’s first examine the basics, starting with moisture. Like us humans, mold also needs water to survive.

It grows whenever there’s a leak, flood, or pretty much any kind of moisture buildup in a given room, more or less severe.

In some climates, it’s enough just for the area to be poorly ventilated for enough moisture to accumulate for mold to use for growth. This is mostly the case with bathrooms and basements.

An optimal indoor humidity levels (which determine how wet an air is) are between 30% and 60%. If your indoor humidity levels are higher than 60%, mold can start to grow.

How do you measure this?

Well, you can simply use a hygrometer or try something called a “soap and squeeze” method, which is more of a DIY approach.

When it comes to temperature, mold typically grows in warmer climates (between 77°F/25°C and 86°F/30°C), but that doesn’t have to be the case 100% of the time.

Some mold species can also grow in colder rooms, explaining, for example, instances of mold on food in the fridge after enough time passes or basement mold problems.

And lastly, we’ll touch on the pH levels. pH is a measure that tells us how acidic or basic (alkaline) a substance is. The pH scale ranges from 0 to 14, with 7 considered neutral. A pH less than 7 is acidic, while a pH greater than 7 is basic.

Most molds tend to grow at pH levels between 5 and 7. 

Nutritional Requirements

Molds are heterotrophic organisms, meaning they obtain their nutrition by breaking down organic matter in their surroundings.

They require organic substrates such as carbohydrates, proteins, and lipids for energy and growth. Common organic materials that support mold growth include:

  • Cellulose, which is found in wood and paper products, including your flooring, drywall, clothing, upholstery, and other items
  • Starches, sources of carbs, found in foods
  • Organic residues, like plant or animal waste


Does mold need oxygen? The answer is yes; mold needs oxygen to grow and survive.

Even if the concentration is low, there needs to be some amount of oxygen present for mold to consume and break down food.


Sunlight contains ultraviolet (UV) radiation, which has fungicidal properties. In layman’s terms, exposure to sunlight and these UV rays can prevent the growth of not only mold but also other microorganisms, like bacteria and viruses.

This is partially the reason why you mostly find mold in darker places, like your basement, cabinets, or anywhere else with insufficient sunlight.

But this also ties to the part where we discussed moisture; these places are also mostly poorly ventilated, allowing for moisture to buildup.

Which is why it’s impractical to try and kill off mold by taking it to sunlight. Instead, reduce moisture levels, dry out the space, and remove any excess water.

Plant Life

Many homeowners are catching on to the trend of houseplants and vertical gardens, which is a good thing, in all honesty, especially in urban places with less nature.

However, note that plant life retains more moisture, which can be problematic if you’re already struggling with maintaining proper humidity levels and preventing mold. 

Place your plants to catch sunlight and ensure good ventilation and drainage.

Ideal Household Settings

Your house has plenty of food and potential moisture sources that can lead to mold. This is why you often see it when there is water damage from plumbing, appliances, or roofing to your drywall, hardwood flooring, and upholstery.

But if you live in a place like Florida, the warm and humid climate can be conducive to mold growth even without a leak. This is why we recommend getting a dehumidifier if you live in such a place to help you combat excess humidity and live in a comfortable, safe setting. 

Keep in mind that a dehumidifier won’t kill the mold you already have; it will just prevent it.

How Harmful Is Mold

Mold can be pretty harmful, especially to those with weaker immune systems, children, and elderly.

Some of the symptoms you may experience:

  • Coughing, wheezing or sneezing
  • Shortness of breath
  • Runny nose
  • Watery eyes
  • Itchy skin
  • Sore throat 
  • Allergic reactions
  • Worsened asthma
  • And worse – read our full guide on how harmful is mold

What to Do About Mold - How to Remove It

As we’ve mentioned before, the key to killing mold is removing the moisture source, whatever it might be:

  • Repair any plumbing or appliance leaks and remove excess water
  • Ventilate the room better and take care of condensation
  • Use a dehumidifier

If you’ve got mold from water damage, you may want to consider hiring a company specializing in water restoration, especially if you’re struggling to repair the leak on your own.

For those with less severe mold problems, white vinegar can do a pretty good job of killing mold.

Mold will not die on its own. You need to put in some work and clean up the mold. Check out our guide on DIY mold cleanup.


That’s it for today! Hopefully, this guide was helpful enough to you to learn how mold develops and what factors determine whether mold will grow or not.

Again, remember, it’s all about moisture. If you’re struggling with mold or water removal, use RepairSprout to find a water damage restoration and mold removal company near you. 

Learn more about mold:

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