How Long Does it Take Mold to Grow?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

A variety of factors determine how long it takes mold to grow.

In most cases, mold can or will grow within 24 to 48 hours, if given favorable conditions to grow in:

  • Dampness, moisture, or high humidity
  • A food source: cellulous material, soap scum, sweat, fruit
  • Oxygen

Variables such as the environment it’s growing in and the surface it’s growing on make a huge difference in terms of the specific timeframe. In some situations, the development of a mold colony will be a very gradual process. In other cases, though, it can show up and begin to expand before you know what hit you.

How does the environment affect mold growth?

For mold to grow, it needs moisture, organic material, and warm temperatures. The organic material can come from a variety of sources, which we’ll cover in a bit.

Regardless of what surface it’s growing on, the speed at which mold develops will depend highly on the amount of moisture it’s exposed to.

In a very damp or humid area with a temperature between 70 to 90 degrees Fahrenheit, mold will flourish.

But if the climate is a bit cooler and/or not quite so humid, the growth process will be slowed. 

How long does household mold take to grow?

Typically, mold will take longer to grow on your household surfaces than it will on things like food or wet clothing. Mold can often show up on the walls or ceilings of the more humid parts of your home, such as your kitchen or bathroom. It can also show up anywhere that’s suffered any flooding or water damage.

Generally, mold in your home will take between 24 and 48 hours to germinate and begin its growth after the moisture and warmth have come together.

Then, it can take anywhere from three to 12 days for those mold spores to colonize, and between two and three weeks for the growth to first become visible. Hopefully, at that point, you’ll notice the mold and take action to get rid of it. If you don’t, though, the rate that it spreads will depend on the temperature and amount of moisture.

How long does mold take to grow on fruit?

Because fruit tends to contain quite a bit of moisture and plenty of nutrients, it serves as an ideal surface for mold to grow on. If you leave your fruit out on the counter during a warm time of year, it will only be a matter of time before the fungus shows up in full force. In fact, if left in a warm environment, fruit can develop visible mold in as little as 24 to 48 hours.

During a colder time of year or if the type of fruit has a lower water content, it may take up to a few weeks before you start to see any mold. One method many people use to keep their fruit mold-free is storing it in the refrigerator rather than out on the counter. During the summer, this is a particularly wise choice!

How long does mold take to grow on bread?

Bread contains plenty of the nutrients that mold enjoys, but it doesn’t contain nearly as much natural moisture as fruit. As a result, you won’t see the fungus show up quite as quickly on your hamburger buns as you will on your strawberries. It’s also worth noting that unsealed bread will develop mold quite a bit more quickly than if it’s fully sealed.

If your bread is left unsealed in a warm, humid setting, you may see mold start to show up in as little as five days. If it’s sealed or left in a slightly more neutral environment, it will likely be somewhere in the range of seven to 12 days.

How long does mold take to grow on wet clothes?

Another common surface where mold often appears is wet clothing. For example, if you let your clothes sit for a long period after washing them or getting caught in a heavy rain, it will only be a matter of time before the fungus starts to grow. However, this is much more common with clothing made out of organic materials, such as cotton, wool, or silk. 

Many homeowners wonder if they can safely leave their clothes in the washer overnight, and the answer is typically yes. While every now and then, wet clothing will start to smell musty after only a few hours, it usually takes at least one full day before mold shows up. Granted, as usual, the amount of moisture and temperature of the environment will factor significantly into that timeframe.