Mushrooms in Terrariums: Should You Worry?

If you have opened, checked, or proudly admired your terrarium and suddenly spotted a tiny mushroom, it can feel a bit alarming. One day there is moss, glass, plants and condensation. The next day, a small yellow mushroom has appeared as if it booked itself in overnight.

The short answer is: mushrooms in terrariums are usually not something to panic about.

They often appear because a terrarium is warm, humid and full of natural organic materials, which is exactly the kind of environment fungi enjoy. Mushrooms do not automatically mean your terrarium is ruined, dirty, or badly made. In many cases, they are simply part of the miniature ecosystem doing its thing.

That said, they are worth paying attention to. Mushrooms can be a sign that your terrarium is staying quite damp, and if they keep coming back, your setup may need a little care adjustment.

2 mushrooms appeared in our 'Leeds' Terrarium. 

Why Are Mushrooms Growing in My Terrarium?

Mushrooms grow from fungal networks that live in organic material. The mushroom itself is only the visible part, a bit like the fruit of the fungus. The rest may be hidden in the soil, moss, bark, wood, or plant matter.

In a terrarium, mushroom spores can arrive through soil or substrate, moss, plants, decorative wood or bark, natural materials used in the build, or even the air while the terrarium is open.

This is especially common in closed terrariums because they hold moisture well. A closed glass environment creates humidity, and many terrarium plants love that. Fungi can enjoy it too.

At Tropical Glass, we often remind beginners that a terrarium is not a plastic ornament. It is a small living system. That means it can change over time. Leaves grow, moss settles, condensation shifts, and occasionally, a mushroom pops up and makes the whole thing feel like it has developed a tiny personality.

A Real Example: Andy’s Chamonix DIY Terrarium Kit

One of our customers, Andy, sent us a photo of his Tropical Glass DIY Terrarium Kit Chamonix after small yellow mushrooms appeared inside.

This is a great example of how mushrooms can show up overnight even in a carefully made terrarium kit. It does not mean Andy did anything wrong. Spores are tiny, natural and very hard to avoid completely when working with living materials.

In Andy’s terrarium, the mushrooms appeared among the moss in a humid closed setup. That tells us the environment had enough moisture and organic matter for fungi to fruit. It is surprising when you first see it, but it is not unusual.

If you are making your first DIY terrarium and something unexpected appears, try not to assume you have failed. Terrariums settle in their own way, especially during the first few weeks and months.

In this kind of situation, our advice is simple: remove the mushroom with clean tweezers if you prefer, check whether the glass is heavily condensed, and briefly remove the lid if the terrarium looks too wet. Then observe it over the next few days rather than making lots of changes at once.

Are Mushrooms Bad for Terrariums?

Usually, mushrooms are not immediately bad for a terrarium.

In many cases, fungi help break down organic material. This is part of how natural ecosystems work. A small mushroom appearing for a short time is often just a sign that the terrarium is alive and active.

However, mushrooms are worth a closer look if they appear again and again, especially if the terrarium smells unpleasant, plants are yellowing or collapsing, the moss is constantly soggy, water is sitting at the bottom, or mould is spreading heavily across the soil, moss, wood, or leaves.

In those cases, the issue is probably not the mushroom itself. It is more likely that the terrarium is staying too wet, has poor airflow, or contains too much decaying material.

Think of mushrooms as a useful little warning light. Not always an emergency, but worth noticing.

Should You Remove Mushrooms from a Terrarium?

You can remove mushrooms from a terrarium if you want to. Most people do, simply because they do not want them spreading spores or changing the look of the display.

You may want to remove them if they are touching delicate plants, getting large, releasing spores, or coming back repeatedly. It is also sensible to remove them if you have curious children or pets at home, or if you simply do not like how they look.

If the mushroom is tiny and the terrarium otherwise looks healthy, you do not need to panic-remove it within three seconds. But removing it is usually the neatest option.

How to Remove Mushrooms Safely

Use clean tweezers or a small terrarium tool. Gently grip the mushroom close to the base and lift it out. Try not to disturb plant roots or pull up too much moss.

After removing it:

• wipe the inside glass if spores or marks are visible
• remove any dead leaves nearby
• let the terrarium air for a short time if it looks very wet
• wash your hands afterwards
• keep the mushroom away from children and pets

Do not eat mushrooms from a terrarium. Even if they look cute, bright, familiar, or “probably fine”, they are not for tasting.

Do Mushrooms Mean My Terrarium Is Too Wet?

Sometimes, yes. But not always. Mushrooms like moisture, so they are more likely to appear in a terrarium that is consistently damp. Closed terrariums should be humid, but they should not be swampy.

Your terrarium may be too wet if you notice:

• heavy condensation all day, every day
• water pooling in the drainage layer
• soggy moss
• soft or yellowing leaves
• a musty or unpleasant smell
• mould spreading quickly
• repeated mushroom growth

A healthy closed terrarium often has some condensation, especially at certain times of day. The glass may mist up and clear again. That is normal.

If the glass is constantly dripping and the moss looks soaked, it may need a little airing. Remove the lid for a short while, then close it again and watch how it behaves over the next few days.

Terrarium care is not about chasing perfection. It is more like gentle observation. The terrarium tells you what it needs if you know what to look for.

If you are unsure how much moisture is right, our guide on how to water a closed terrarium explains what healthy condensation looks like and when to hold back on watering.

How to Reduce Mushrooms Coming Back

You may not be able to prevent mushrooms completely, especially when working with natural materials. But you can reduce the chances of them returning.

Keep Watering Light

Overwatering is one of the most common terrarium care mistakes. Closed terrariums recycle moisture, so they usually need far less water than people expect.

If your terrarium is already humid, do not add more water just because the surface looks slightly dry. Check the overall condition first.

Use Bright, Indirect Light

Most enclosed terrariums do best in bright, indirect light. Direct sunlight can overheat the glass and stress the plants. Too little light can weaken plants and slow healthy growth, which may lead to more decaying leaves. 

A bright room, away from harsh direct sun, is usually a good place to start.

Remove Dead Leaves

Dead leaves are natural, but they can feed mould and fungi if left to break down inside the terrarium.

Use tweezers to remove yellow leaves, fallen leaves, mushy plant material, decaying moss patches, or anything that smells bad.

This small habit makes a big difference.

Air It Briefly If Needed

If the terrarium looks too wet, open it for a short period to let excess moisture escape. This might be 30 minutes, a few hours, or longer depending on how wet it is.

Do not leave a closed terrarium open permanently unless you are deliberately changing how it is kept. The goal is to rebalance it, not dry it out completely.

Be Careful With Extra Natural Materials

Adding random outdoor sticks, bark, soil, or stones can introduce more spores, pests, or unwanted organisms. Natural materials can look lovely, but they are not always ideal for a closed terrarium unless they have been chosen and prepared carefully.

Mushrooms vs Mould vs Algae in a Terrarium

It is easy to mix up mushrooms, mould and algae in a terrarium, especially when everything is small, damp and growing close together.

Mushrooms

A mushroom usually has a clear shape, often with a tiny stem and cap. It can appear quite suddenly, especially in a warm, humid closed terrarium.

Mould

Mould often looks white, grey, dusty, fluffy, or web-like. You may see it on wood, moss, soil, fallen leaves, or other decaying material.

Algae

Algae usually looks like a green film or coating on the glass, moss, stones, or surface of the substrate. It often appears when there is steady moisture and enough light.

If you are not sure what you are looking at, take a clear photo in natural light before removing it. That makes it easier to compare later or ask for advice.

Can Mushrooms Harm Terrarium Plants?

Small mushrooms do not usually harm healthy terrarium plants directly. The bigger concern is the condition that allowed them to appear.

If your plants are happy, upright and growing, and the mushroom appeared briefly, it may not be a serious issue.

If your plants are struggling at the same time, check for overwatering, poor light, rotting roots, decaying leaves, too much condensation, lack of airflow, or plant choices that are not well suited to a closed terrarium.

Closed terrarium plants usually prefer humidity, but they still need balance. Ferns, fittonia and many mosses can enjoy humid conditions, while plants that prefer dry air are better suited to open terrariums.

Are Mushrooms in Terrariums Dangerous?

It is best to treat all unknown mushrooms with caution.

The main risk is ingestion, especially by children or pets. Some yellow houseplant mushrooms, including mushrooms that may be Leucocoprinus birnbaumii, are not considered safe to eat and may cause stomach upset if swallowed. The mushroom simply sitting inside the glass is usually less of a concern than someone or something trying to nibble it.

If you remove mushrooms, use clean tweezers or gloves, dispose of them safely, and wash your hands afterwards. Simple, calm, sensible.

What If Mushrooms Keep Coming Back?

Quick Terrarium Mushroom Diagnosis

Quick Terrarium Mushroom Diagnosis

Final Thoughts

Mushrooms in terrariums can look dramatic, but they are often more interesting than worrying. They are a sign that your little glass garden is full of natural life.

A single mushroom does not mean your terrarium is ruined. Remove it if you prefer, check the moisture level, clear away dead leaves and keep an eye on how the plants are doing.

If you are new to terrariums, this is all part of learning how a living system behaves. Sometimes it grows beautifully. Sometimes it fogs up. Sometimes it produces a surprise mushroom and makes you question everything before breakfast.

FAQ

Are mushrooms in a terrarium bad?

Not always. A small mushroom is usually not a disaster and can simply be part of the natural ecosystem. If mushrooms appear often, or your terrarium smells bad or looks soggy, check the moisture level and remove any decaying material.

Should I remove mushrooms from my terrarium?

Yes, you can remove them with clean tweezers. This helps keep the terrarium tidy and reduces the chance of spores spreading. Try not to disturb plant roots or moss too much.

Why did mushrooms appear in my DIY terrarium kit?

Mushroom spores can be present in soil, moss, plants, wood, or the air. A closed terrarium is humid and warm, so spores may occasionally fruit into visible mushrooms. It does not mean you have done anything wrong.

Can mushrooms kill terrarium plants?

Small mushrooms do not usually kill healthy plants directly. However, repeated mushroom growth can be a sign that the terrarium is too wet or has too much decaying organic matter, which can stress plants over time.

Are terrarium mushrooms poisonous?

Unknown mushrooms should always be treated with caution. Do not eat mushrooms from a terrarium, and keep them away from children and pets. Remove them with tweezers and wash your hands afterwards.

How do I stop mushrooms growing in my terrarium?

You may not stop them completely, but you can reduce them by avoiding overwatering, removing dead leaves, keeping the terrarium in bright indirect light, and airing it briefly if it becomes too wet.