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Why Your Terrarium Fogs Up And How You Can Prevent It

So you put together your terrarium and now you’re noticing that it’s all clouded up with fog, tarnishing that piece of artwork that you work so hard to put together. Luckily, there are a few simple ways you can resolve this issue.

Terrarium fog can be prevented by lowering the water levels, cleaning the container with soap, or using an anti-fog spray. Terrarium fog is a natural process that is caused by condensation on the container. Small levels of condensation will not be harmful to your terrarium.

But before you go ahead and start buying bottles of antifog, you want to make sure that you are not putting a temporary fix on a symptom of a deeper issue with your terrarium.

How to prevent your terrarium from fogging up

Let’s cut straight to the chase. There are two main ways to address terrarium fog: reduce the water levels or stop compensation droplets from forming.

The first thing that you look at is reducing the water levels. I’ll explain why below.

Lower the water levels in your terrarium

Open up your terrarium and let it air out for a few hours. That’s going to allow excess water vapors to escape from your terrarium, leaving less water to leave condensate on the inside of your container.

For good measure, you can also get a paper towel or a piece of cloth and wipe off excess condensation that you see in the container.

Having a lot of fog or condensation in the terrarium is not only a visual nuisance, but it’s also a sign of overwatering. That’s one of the most common mistakes terrarium builders can make.

Overwatering your terrarium can lead to issues like root rot and mold growth. If this goes on for too long, your plants might begin to turn shades of yellow and start looking droopy.

Another way you can check for signs of a watering is to feel the soil of the terrarium. If it feels soaking wet, that’s a telltale sign that there’s too much water in your terrarium.

You know you have just the right amount of water in your terrarium when your soil feels slightly moist, but not soggy. In this scenario, you should only be seeing slight condensation in your container in the mornings and evenings.

Clean the inside with soap water

Another neat trick you can try to clear up the fog is to clean the inside of your container with soap water.

Without going into too many details about surface tension, degree of wetting, and intermolecular forces (I took a graduate level course on that in college), basically the soap makes the water form a smooth film instead of tiny droplets on the container

Hint: it’s essentially the same mechanism behind why a paperclip will float on regular tap water, but not on soapy water. Answer: by reducing the surface tension of water.

The soap doesn’t make the water disappear or stop condensing on the container, but it makes the condensation almost completely transparent, as if it weren’t there. 

A little background if you’re interested: the reason that the condensation “fog” blocks your vision is because of the tiny droplets that get formed. These droplets distort the light in all sorts of different directions as it passes through their high surface area.

When the water is instead in a thin film, the light still gets slightly distorted, but it’s all in the same direction. This means that the light that you see will be completely clear.

Spray some Anti-fog cleaner on the inside of your terrarium

Another way to prevent your terrarium from fogging up is to use anti-fog cleaner. Just spray or wipe a little bit on the inside of your container, and you shouldn’t see anymore terrarium fog.

Anti-fog sounds fancy and professional, but the science behind how it works is very similar to what I explained when using soap water to clean your container. 

If I had to guess, you might have slightly better chances of getting the results you want with anti-fog cleaner compared to using soap water. This is based on the assumption that the cleaner has been engineered and optimized for this specific purpose while soap is more of a DIY solution that “just works”.

The only caveat I would consider with using anti-fog cleaner is that you are introducing unknown chemicals into your terrarium. It’s not entirely clear how that’s going to affect your plants

If possible, try to find one that says that it’s non-toxic. That’s probably going to reduce the risk of something bad happening to your plants.

To be fair, anti fog is often used for glasses and goggles. So I’m imagining if it’s safe for your eyes, it’s probably safe for your plants, especially if you aren’t spraying it directly on your plants. But no guarantees.

Another thing to note: anti-fog is not permanent. It usually lasts for about a few months, after which you’ll probably have to apply it again. 

Where does the fog in your terrarium come from?

If you’re interested in learning more about why your terrarium fogs up, there’s two explanations. 

The main culprit is condensation, but another (less likely) possibility is mineral deposits left behind from the condensation.


The main culprit behind the fog is condensation.

If you think back to your middle school science class, condensation is what happens when water vapors in the air cool down enough to turn into a liquid. 

This usually happens when the water vapor is coming in contact with a cold surface, like glass on a cold day.

So just to be clear, the fog that you see isn’t leftover water from your last watering session and it’s not water that’s “leaking into” your terrarium.

The condensation results from the cycling of water within your terrarium. Liquid water evaporates, then recondenses, forming tiny water droplets in an unending cycle within your terrarium.

These water droplets distort light passing through your terrarium, causing that foggy look that you see.

Condensation is a completely natural part of building a terrarium. It’s why they require so little maintenance. Having a little bit of condensation is not “bad” for your terrarium.

If you wanted to, you could just ignore the fog that you see and be on your merry day. It’s nothing more than something that blocks your vision a bit at some times of the day.

However, if you are seeing heavy condensation all day long every day, that’s a sign your terrarium is over watered (which is “bad” for your terrarium).

Mineral deposits

Another possible (but unlikely) cause of terrarium fog is mineral deposits left behind by condensation.

If there were any minerals or salts that were dissolved in water and got carried along with the water vapors, it’s possible that they might have built up over time over many cycles of evaporation and condensation within your terrarium.

If you’re noticing that your container is still cloudy after a quick wipe, this could be the culprit. It might take a little bit more vigorous scrubbing to get it off of your container.

If you can, you should clear this up if you start to notice it so that your plants are getting adequate amounts of light passing through the container. Otherwise, the mineral deposits might block out a little bit of the light passing through.

That’s pretty much all I have to say about terrarium fog. If you want to learn more about terrariums, feel free to check out some of the related articles below.