Terrarium Maintenance: Preventing Mold and Fungus

Keeping a terrarium clean and free of mold is essential. The best way to prevent mold growth in a glass terrarium is to minimize the moisture, excessive heat, and light by limiting it to only the amount that plants need to thrive.
An open terrarium with succulent.

Having a terrarium is one of the best ways to bring a beautiful combination of outdoor scenery into your home. However, taking care of your terrarium may be an uphill task, especially for beginners. If you don’t take proper care of your terrarium, it can become overrun with mold and fungus. In fact, mold is the biggest threat to every terrarium since it steals away all nutrients leaving your plants malnourished. With time, your plants will wither, toppling over the entire ecosystem.

So, what can you do to prevent mold and fungus in a terrarium? Consider adding springtails to your terrarium and avoid overwatering. Springtails are tiny insects that love feeding on fungi and other decaying matter. They are a mold’s arch nemesis. Always apply fungicide to your terrarium substrate, remove all dead or decaying plant matter, and give it enough light. You can also prevent mold growth by sterilizing your substrate before adding it to the terrarium, airing it out periodically, and ensuring adequate drainage.

This blog post discusses everything you need to know about preventing mold and fungus in a terrarium. Read on to learn more.

Why Does Mold Grow

Before we start discussing strategies for preventing mold growth in a terrarium, it is essential to understand why mold thrives in terrariums.

Typically, mold loves warm, damp, and dark places with minimal air circulation. It can quickly grow on any moist surface, but its growth rate increases exponentially when the substrate has high organic content.

A standard terrarium experiences a lot of moisture circulation that helps to keep the water cycle working properly.

Mold also uses plant material as nutrients, so if there is no other source of nutrition, they will start feeding on your plants. That’s why keeping the terrarium clean and free from any dead or decaying matter is crucial.

A jar converted in to a closed terrarium.
The temperature, humidity, and organic matter in a terrarium create an ideal environment for mold growth.

Closed terrariums are at an increased risk of experiencing mold and fungus issues because the temperature is always perfect.

Due to the greenhouse effect, it will always be warmer in a closed terrarium, providing the perfect conditions for mold growth.

Furthermore, the relative humidity is quite high in a closed terrarium, making it even more susceptible to mold and fungus growth.

In short, the temperature, humidity, and organic matter in a terrarium create an ideal environment for mold growth. To prevent this, you need to ensure that your terrarium is properly ventilated and not too moist.

Tips For Preventing Mold Growth in A Terrarium

Now that you understand why mold grows in a terrarium, let’s look at some tips for preventing mold growth and fungus.

Tip #1: Ensure You Have a Drainage Level in the Terrarium

One of the most crucial steps to take to prevent mold growth in your terrarium is to make sure you have a drainage level.

The primary purpose of the drainage level is to catch excess water. Since there are no drainage holes in most terrariums, you must find a way of catching the excess water in your drainage layer. This will play a critical role in preventing it from causing mold growth in your terrarium.

To make a drainage level, you first need to prepare your terrarium container and then fill the bottom part with rocks or sand.

The material you use for your drainage layer may depend on the general design of your container. You may even pick different color sand or rocks. The primary objective is to create a clear distinction.

Cactus terrarium.
You first need to prepare your terrarium container and then fill the bottom part with rocks or sand.

Once you have a drainage layer, put a divider on top to separate the drainage layer from the charcoal level. This technique also prevents seeping.

For a divider, feel free to use cheese gauze or cloth, a coffee filter, construction paper, or something similar.

Avoid using something that might block water from passing through the divider. The charcoal layer goes right below the divider.

Expert gardeners prefer using charcoal because it soaks in a wide range of impurities and also plays a critical role in eliminating bad smells in your terrarium.

It also helps fight fungus and mold growth. You can add some potting mix on top of the charcoal layer.

Tip #2: Add Springtails to Your Terrarium

Springtails are tiny, white bugs that can survive in damp conditions. They are also efficient at removing fungus gnat larvae and other small pests in your terrarium.

These harmless creatures play a critical role in controlling mildew, mold, and other organic matter by consuming them before they cause any harm to your plants or terrarium decorations.

Tip #3: Avoid Overwatering Your Terrarium

Overwatering is one of the leading causes of mold and fungus growth in a terrarium. When you overwater your plants, the excess water remains stagnant for too long, encouraging growth of unwanted organisms like mold and fungus.

It’s essential to make sure that your terrarium plants have enough water but not too much of it.

A person watering the terrarium.
Overwatering is one of the leading causes of mold and fungus growth in a terrarium.

Consider adjusting the watering schedule based on several factors, such as the type of plant, the time of year, and the terrarium’s size.

Tip #4: Avoid Mixing Plants with Different Care Requirements

Choosing the right plants is one of the most critical decisions you need to make when designing a terrarium. You can make a fatal mistake if you are not careful. Generally, you should never mix plants that have different care requirements.

For instance, don’t mix succulents with cold-tolerant plants in a closed terrarium since it will lead to root rot and complex mold issues.

Keep in mind that succulents love well-draining soil and less moisture. Therefore, mixing them with air plants or moss plants doesn’t make sense.

Air plants don’t require soil since they get all the essential nutrients they require from the air.

A cactus terrarium hanging,
You should never mix plants that have different care requirements.

If you must mix them with succulents in your terrarium, they should be placed on top of another object instead of planting them directly in the soil.

Otherwise, feel free to use dry fillers such as pebbles, stones, dry preserved moss, pumice, or crushed oral in an air plant-only terrarium. The dry fillers are critical in preventing mold growth and root rot.

Avoid putting succulents in closed terrariums since they need more air circulation and less humidity. Instead, use an open-top terrarium for them.

Tip #5: Remove Dead Leaves

If any of your plants has shriveled leaves or other signs of decay, you must remove those leaves as soon as possible.

Dead leaves can quickly invite pests and mold into your terrarium. It is also essential to remove any roots that have gone bad.

Keep in mind that fungi feed on decaying matter. Therefore, if you don’t take steps to remove decaying matter from your terrarium, the fungus will only spread faster.

Tip #6: Apply Fungicide to Your Substrate

If you notice any kind of mold or fungus in your terrarium, it’s best to use a fungicide treatment as soon as possible. Fungicides help control and prevent the spread of fungal diseases in your terrarium.

Choose an organic fungicide safe for your plants and animals. Applying the fungicide directly to the substrate is the best way to control and prevent the spread of fungus in your terrarium.

Tip #7: Prune Your Plants Regularly

Pruning your plants regularly is another effective way to prevent mold growth in your terrarium.

While pruning encourages healthy new growth in plants, it also helps remove dead leaves and stems that could act as food for fungus.

By pruning your terrarium plants regularly, you can keep the air circulation going properly and limit the spread of mold growth in your terrarium.

Tip #8: Replace the Soil

Some types of soil usually have mold spores causing mold growth in your terrarium. If this is the case, you should consider replacing the soil with a fresh one to eliminate mold spores.

You can also try adding some activated charcoal or perlite to your soil mix to help absorb extra moisture and reduce chances of mold growth.

Both of these materials provide excellent drainage and aeration, which prevents mold growth.

You can also kill spores and pathogens by baking your soil at 300 degrees Fahrenheit for at least 30 minutes. Baking will sterilize your potting mix, making it safe for your terrarium.

Tip #9: Increase Air Circulation

Mold loves moist environments where air circulation is limited. Ensure you have proper air circulation in your terrarium by providing adequate ventilation, such as using open-top terrariums or adding a fan to blow fresh air into the closed container.

A glass hexagon terrarium.
Ensure you have proper air circulation in your terrarium.

This will help to keep the air in your terrarium fresh and reduce the risk of mold growth.

You should also ensure you don’t overcrowd your terrarium with too many plants, which can restrict air circulation and lead to mold problems.

Tip #10: Monitor Your Terrarium Regularly

Finally, it is imperative to keep an eye on your terrarium and monitor it regularly. Check for any signs of mold or fungus and act immediately if you find anything suspicious.


Mold and fungus growth can quickly become a significant issue in your terrarium if it’s not managed correctly.

Fortunately, there are several steps you can take to prevent and control the spread of mold growth in your terrarium.

Follow the tips above to keep your terrarium clean and healthy, so it can remain a beautiful display of plants for many years.

Last update on 2023-12-11 / Affiliate links / Images from Amazon Product Advertising API

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