How to Make a Closed Terrarium That Lasts for Years

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

When built properly, they can look after themselves for years with very little input from us – because the system is doing the work for you.

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.

A closed terrarium doesn’t give you many controls, and that’s kind of the point.

Once the lid goes on, the system has to regulate itself. The plants, materials, and (if you’re using them) bioactive bugs you choose to put inside all need to work together over the long-term.

That’s why it’s worth thinking about the system as a whole right from the beginning.

In practice, these systems reward careful setup far more than active correction. More often than not, it’s actually the overwatering, tweaking, or well-intentioned “help” that nudges things out of rhythm in the first place.

So if there’s one guiding principle, it’s this: set it up so you can leave it alone.

Get that part right, and the rest becomes much simpler.

Once a closed terrarium is sealed, things start to settle into a familiar rhythm.

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 scientific guide on how terrariums work.

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 is your moisture buffer.

Use LECA clay balls to create a base reservoir, around 1 inch (2 cm) deep. In a sealed system, excess water has nowhere to escape, so this layer gives it somewhere to collect instead of saturating roots.

There are a variety of ways to build a false bottom/drainage layer – and you can use other strong, porous materials – but even this simple LECA layer goes a long way.

2. Barrier/Separation Layer

This layer sits between the drainage material and the substrate above.

Its job is simple: keep the two layers distinct over time. Without some form of separation, fine particles gradually work their way down into the drainage layer, compromising its effectiveness and compacting the base of the build.

You can use a fine mesh barrier or a thin layer of long-fibre sphagnum moss. Both achieve the same goal.

In our builds, we tend to prefer mesh because it holds its structure indefinitely and doesn’t decompose. Sphagnum works well too, but it will slowly break down as the system matures.

3. Activated Charcoal (*Optional but Recommended)

Activated charcoal can sit above the mesh as a distinct layer, or it can be sprinkled elsewhere throughout the layers.

In a closed environment, it helps adsorb impurities and organic compounds as water cycles through the substrate. It’s not a substitute for good structure, but it adds an extra buffer against stagnation and odor.

It’s not an exact science, but a thin, even layer is enough.

4. Substrate Layer

The substrate is where your plants will live and root.

Add enough substrate to comfortably support the roots of your largest plant – usually around 3–4 inches (7–10 cm), depending on container size. It should be deep enough to anchor plants securely, but not so deep that it dominates the vertical space.

You typically want these layers combined to take up around 1/4 of the container to maintain visual balance – you can also slope the substrate from back to front to maximize visual depth without adding more material.

5. Hardscape & Surface Layer

Hardscape gives the terrarium its physical framework and sense of flow.

Rocks and wood aren’t just decorative – they create anchor points for roots and shape the overall growth pattern of the build.

Place and secure hardscape before planting. Once roots establish, repositioning larger elements can disturb far more than it appears. Anchor pieces firmly into the substrate so they won’t shift as the system matures.

Once the structural elements are set, the terrarium is structurally complete and ready for planting.

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.

Once a closed terrarium is established, the job changes.

You’re not really “looking after” it in the traditional sense anymore, or following a care routine. You’re paying attention to how the system is behaving – how moisture is cycling, how plants are growing, how the glass looks throughout the day.

Some variables are (mostly) best left alone once they’re set. Others, like positioning and light, are easy to adjust if growth looks unbalanced. The trick is knowing the difference.

Most of the time, small, deliberate changes are enough. Closed systems don’t usually need dramatic fixes – just occasional nudges in the right direction.

Watering

Water is the variable that makes or breaks most closed terrariums.

Once the lid goes on, you’re not following a watering schedule anymore. You’re setting the moisture level for an enclosed system that will recycle that water on its own.

In our experience, most long-term issues trace back to starting too wet rather than too dry. A lightly moist substrate is enough. It should feel damp, not saturated. Excess water has nowhere to drain and can take a long time to work itself back into balance.

In practice, condensation levels are a better indicator of balance than soil moisture.

If you ever do need to add water later on, add less than you think. A small adjustment is usually all it takes. It’s easy to add more. It’s surprisingly difficult to take it back out.

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

Oh, and don’t use tap water. The minerals in tap water will cause a buildup on the glass that can make it look smeared – use distilled water where possible.

Lighting

Lighting is often the most overlooked variable in a closed terrarium.

It’s the easiest to adjust, but not the easiest to get right (and it’s constantly changing through daily and monthly cycles).

Closed terrarium plants consistently perform best in bright, indirect light. Near a window is usually ideal, but out of direct sun. What tends to work best over time is consistency. Steady, moderate light produces compact, balanced growth.

The advantage is that light is easy to tweak. Move it slightly closer. Pull it back a touch. Add a soft grow light if natural light is limited. Small adjustments tend to show results within weeks.

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.

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 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.

Bioactivity

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

Springtails help complete the nutrient cycle by consuming mold and breaking down 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.

Springtails can thrive in closed terrariums because their food source is constantly produced, and plants can keep up with their oxygen needs. They don’t need feeding schedules or active care – they simply become part of the system.

Isopods can also work in closed terrariums, provided there is some level of air exchange. A partial seal or occasional opening allows enough airflow for them to remain healthy over time.

Larger animals, however, aren’t suited to fully sealed environments. Closed terrariums are designed as plant-led ecosystems. They don’t provide the airflow, space, or environmental control that reptiles, amphibians, and larger bug pets (e.g., beetles) would require.

If you’d like to explore how living cleanup crews and nutrient cycling shape these systems more deeply, we’ve covered that in our guide to building a living, bioactive terrarium.

Longer than you might expect.

When a closed terrarium is structured properly, it can absolutely last for years.

In practice, the ones that last all share the same foundations. A drainage layer that actually absorbs excess moisture. A substrate that stays airy instead of compacting. Plants that don’t outgrow the space within months. Steady light instead of dramatic swings.

Get those right, and the system slowly settles into rhythm.

That doesn’t mean nothing ever changes. Plants grow. Moss thickens. You may trim occasionally. But a well-built closed terrarium shouldn’t feel fragile or high-maintenance. It should feel steady.

There are even documented sealed terrariums that have been going for decades without ever opening them. Are they in pristine shape? Not exactly – most have taken on a particular wildness, but that’s part of the fun. Watching our creations grow and evolve.

We’ve written more about what actually determines terrarium lifespan if you’d like to go deeper.

The builds that last aren’t the ones that are constantly corrected. They’re the ones that were thoughtfully designed from the start – and then allowed to do what natural systems tend to do when they’re not over-managed.

Build it once with care. Then let it settle.