How to Make a Closed Terrarium (That’s Built to Last)

A closed terrarium is a sealed, self-watering miniature ecosystem.

When they’re built properly, they can thrive for years with very little intervention. And that’s something we’ve seen again and again.

The catch is that long-term success is almost always decided early on. Most issues we see aren’t sudden failures – they’re early setup mistakes that quietly compound over time.

So, in this guide, you’ll learn how to make a closed terrarium properly, step by step. From selecting the right container and plants to balancing moisture, light, and airflow inside a sealed system.

Whether this is your first sealed terrarium or one you’re rebuilding after a few missteps, this is the same approach we use for all of our stable, long-lasting setups.

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Closed terrariums are simple systems, but they do have a few built-in constraints worth understanding upfront.

Once you get how they behave, most of the decisions you’ll make – what to plant, how much to water, when to step in – start to make sense on their own.

At their core, closed terrariums work by trapping moisture inside the container. That sealed environment creates the warm, humid conditions that tropical plants love. A bit like a forest floor in miniature.

Here are some basic principles that won’t let you down.

• Plant choice matters more than plant care. In a closed terrarium, small, slow-growing plants are far easier to manage than fast growers that quickly outgrow the space.
• Most long-term success comes down to moisture control. Water is very easy to add and surprisingly difficult to remove once it’s inside, so starting conservatively usually saves headaches later.
• Problems usually come from imbalance, not neglect. Closed terrariums rarely fail because they’ve been left alone. More often, it’s too much watering, tweaking, or “helping” that throws things off. In many cases, the best thing you can do is… nothing at all.

Once a closed terrarium is sealed, a fairly predictable set of internal processes begins.

Water evaporates from the substrate and plant leaves, condenses on the glass, and then drips back down into the soil. Over time, this creates a closed-loop water cycle that keeps plants hydrated without you needing to water them directly.

This self-contained cycle is what allows closed terrariums to remain stable with very little ongoing input.

It’s also why plant choice, substrate structure, and moisture balance tend to have bigger consequences than they do in open setups. In a sealed system, everything is connected.

This is where going bioactive can make a real difference, too.

Beneficial microorganisms and clean-up crews help break down organic waste, suppress mold, and recycle nutrients back into the system. In a well-balanced terrarium, they quietly handle much of the work that would otherwise require intervention.

If you want a deeper look at what’s happening inside the glass, we break these processes down in more detail in our guide on how terrariums work (written by a scientist. Yes, that’s me!).

Let’s start with the essentials.

Most closed terrarium builds rely on the same core components. While there are a few valid material options in each category, every successful sealed terrarium needs drainage, structure, and the right growing medium.

And yes, a bit of flair doesn’t hurt either…

Essential Closed Terrarium Supplies

• Clear glass container with a lid (or fitted acrylic lid).
• Drainage material – LECA clay balls or lava rock.
• Tropical terrarium substrate – free-draining but moisture-retentive.
• Hardscape – rocks, cork bark, or wood.
• Closed terrarium plants – compact tropical species.
• Springtails – critical for mold control, beginner-friendly species.
• Basic tools – long tweezers, scissors, spray bottle.

We sell most of these terrarium supplies on the Terrarium Tribe store, but you don’t need anything crazy exotic to get started.

A Few Notes Before You Buy

We’ve built countless terrariums over the years, and the same patterns show up in the materials we use.

In our experience, LECA consistently outperforms gravel in closed terrariums. The porosity of the clay balls improves airflow, and they actively absorb moisture instead of just letting it pool below the substrate. That alone goes a long way toward reducing root rot over time.

The substrate is just as important. Most closed terrarium problems trace back to soil that holds too much water or compacts over time. A proper tropical terrarium mix sets the foundation for everything that follows.

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As for containers, good closed terrarium glassware turns up in unexpected places. Apothecary jars, spice jars, whisky bottles, and even old candle jars can all work well (as long as they’re clean and can hold humidity reliably).

We cover this in detail in our guide to choosing the right terrarium container.

And despite what you might expect, containers don’t need to be perfectly airtight. A loose-fitting lid that retains humidity is often more than enough.

If you find a container you love that doesn’t come with a lid, acrylic disc lids cut to size are often the simplest and cleanest solution.

Building a closed terrarium is a lot like building a house.

You’ll need a good foundation, lots of support, and plenty of drainage. The structure is key, with each of the distinct terrarium layers playing a specific role in moisture control and plant health.

1. Drainage Layer

This layer acts as a reservoir for excess water.

• Use LECA if you can.
• Aim for 1 inch (2 cm) depth.

Over the long term, a lack of drainage causes more root rot than any other single factor. It’s not glamorous, but this stage is one of the key decisions you’ll make.

That’s why the type of false bottom/drainage layer you choose really matters.

You can stop here with a simple LECA layer, or you can also consider adding a mesh barrier to separate the drainage material from the next layer. And if you’d like to add activated charcoal to your terrarium (to help keep things clean and fresh), here’s a good place to create your layer (on top of the mesh).

2. Substrate Layer

The substrate provides physical and nutritional support for your plants, i.e., the medium you plant in.

• Use a tropical terrarium mix (not potting soil).
• The depth should comfortably allow for the roots of your largest plant.
• Typically 3-4 inches (7–10 cm) depending on container size.

Having the right mix of structure, drainage, and fluffiness (for plantability) is key here.

3. Hardscape

Hardscape is what gives the terrarium its structure, scale, and sense of flow.

• Add rocks and wood before you plant anything.
• Anchor pieces firmly into the substrate so they don’t shift later.

Trust me, this step is much easier to get right before plants are in the way.

4. Closed Terrarium Plants

When it comes to planting, getting the right order really smooths out the process.

• Start with the tallest plants first, then work down to smaller accents.
• Be intentional with your feature plants and pops of color.
• Plant vines last (you can often just lay them on top).

Planting in a confined space can be surprisingly finicky, especially if you’re bare-rooting plants beforehand. So try to give your hands and your plants a little breathing room.

5. Finishing Touches

Cover the surface with moss to seal the deal and bring the whole scene to life.

Then any leaf litter, bioactive elements (e.g., seed pods), and final details. Natural or otherwise. Dinosaur figurines absolutely count.

Then seal the terrarium, you’re done!

The best plants for a closed terrarium are compact tropical species that tolerate high humidity, low airflow, and indirect light.

Rather than thinking in terms of individual species straight away, it helps to think in broad plant types. The combinations tend to work better.

Good closed terrarium plant categories include:

• Ferns
• Vining plants
• Foliage plants
• Tropical mosses
• Small epiphytes

What doesn’t work are plants adapted to dry conditions. Succulents and cacti rot quickly in sealed environments, no matter how carefully you water them.

For specific species recommendations and growth habits, see our hand-picked list of the best closed terrarium plants.

Keeping a closed terrarium ecosystem running smoothly over the long term isn’t about constant tweaking – it’s shaped by a few core choices around plant size, lighting, and bioactivity. Together, they determine how the system behaves once it’s sealed.

Get those right, and you’re well on your way to a true self-sustaining terrarium.

Plant Size

Plant size is probably the most important factor here.

Choosing species that naturally stay small sets the ceiling for how much maintenance the terrarium will ever need. Managing growth from the start is far easier than constantly cutting plants back once everything fills in.

Lighting

Bright, indirect light is ideal.

• Avoid direct sun. Most tropical plants can’t handle it.
• Consistency over intensity.

Lighting is best treated as a setup decision, not something you’re constantly tweaking. Most closed terrariums struggle because they’re placed too cautiously, rather than too brightly.

Steady, moderate light almost always works better than playing it too safe.

Bioactivity

This is where sealed terrariums really start to look after themselves.

Springtails help complete the nutrient cycle by breaking down mold and decaying organic matter before it becomes a problem. They’re especially useful in the first few weeks, when new setups are still finding their balance.

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Controls mold • Self-maintaining

This approach is often referred to as a bioactive terrarium, where the ecosystem quietly handles much of its own maintenance over time.

Once a closed terrarium is established, day-to-day care is pretty minimal. Most of the work is simply paying attention and making small corrections when needed.

Watering

In a sealed terrarium, condensation tells you far more than the soil ever will.

• Light fogging on the glass during the warmest part of the day is normal and healthy.
• No condensation at all usually means the system needs a little water.
• Heavy dripping or constant fogging is a sign that there’s too much moisture trapped inside.

In practice, condensation is a better indicator of balance than soil moisture, which can be misleading in enclosed setups.

If you do need to water, add it slowly. It’s easy to put more water in, and surprisingly hard to take it back out once it’s there.

For a more detailed walkthrough, see our guide on how to water a terrarium.

Common Closed Terrarium Problems (and Fixes)

Nearly all closed terrarium issues fall into a few familiar patterns. Once you know what to look for, they’re usually straightforward to correct.

Too much condensation

If the glass is heavily dripping or fogged, there’s too much moisture trapped inside.

This usually isn’t a big deal. Cracking the lid for a short while to let some humidity escape is often enough to bring things back into balance.

No condensation

If the glass stays completely clear, the system is likely running too dry. You definitely want to see a light fogging of the glass throughout the day. Add a small amount of water and give it time to re-establish the water cycle.

Our guide to terrarium condensation walks through all aspects, from too much to too little.

Mold growth

A bit of mold is very common in new terrariums, especially in the first few weeks.

Most of the time, it settles on its own as the system stabilizes (give it a few weeks). That said, introducing springtails can really help get on top of mold in the long term. The earlier you can add them, the better.

Our guide to mold in terrariums outlines everything you need to know.

Yellowing plants

This one can be frustrating, because it doesn’t always have a single cause. In closed terrariums, though, it’s often down to light rather than water. If growth looks pale or weak, try nudging the light levels up slightly before changing anything else.

That’s everything you need to build a stable, self-sustaining closed terrarium.

Just remember, the ones that last aren’t constantly tweaked or fussed over. They’re built with the right structure from the start, then given time to settle and find their balance.

Start simple, make deliberate choices early on, and let the ecosystem do what it’s designed to do.

Need a bit more guidance on the actual building part? If you want a fully illustrated, beginner terrarium build guide, we walk through the entire process from start to finish.