You followed the tutorial step by step. Pebbles at the bottom, a sprinkle of charcoal, potting soil on top. You sealed the lid with such excitement, imagining a tiny rainforest that would run itself for months. Two weeks later, you’re staring at foggy glass that never clears, brown leaves melting into mush, and a smell that makes you want to chuck the whole thing in the trash.
Here’s what nobody told you: the layers aren’t the problem. It’s that every guide treats them like a craft project instead of what they really are, a working water cycle trapped in glass.
We’re going to build this together, from the bottom up. You’ll understand not just what goes where, but why each layer exists, how water actually moves through a sealed jar, and the one tuning step that separates thriving terrariums from swampy disasters. By the end, you’ll have a blueprint that works because it respects the physics of a closed world.
Keynote: Closed Terrarium Soil Layers
Closed terrarium soil layers create a self-sustaining water cycle when built with precise depth ratios. The system requires LECA drainage (1-2 inches), barrier mesh, charcoal filtration (0.5 inches), and aerated substrate (2-3 inches) that resists compaction. Success depends on understanding how water moves through sealed ecosystems, not just stacking materials.
The Secret Life of Water in a Sealed Jar
Your Terrarium Isn’t a Pot, It’s a Planet
Think about what happens when you trap moisture inside glass with no escape route. Water never leaves. It only cycles between the glass walls, the humid air, and the soil below.
Your plants breathe out moisture through their leaves all day long. That water vapor hits the cool glass and condenses into droplets. Those droplets run down the sides like rain, soaking back into the substrate. The cycle repeats endlessly. It’s a miniature weather system with perfect recycling and zero waste.
But here’s the catch. If any part of that cycle gets stuck, the whole system floods or dries out.
Why “Just Add Drainage” Can Actually Make Things Worse
I learned this the hard way when I built my first large closed terrarium. Added three inches of river rocks like the internet told me to. Felt so proud of that drainage layer. Six weeks later, I could see standing water at the bottom that never went anywhere, and my fittonia was rotting from the roots up.
In open containers, drainage works because excess water escapes through holes in the bottom. In sealed systems, water pools at the lowest point with nowhere to go. The humidity stays trapped above. Roots sit in waterlogged soil breathing humid air, which is basically a suffocation sandwich.
Too much drainage actually creates stagnant puddles in containers under six inches tall. The soil above stays wet because water can’t drain into an already-full reservoir. This is called a perched water table, and it’s the silent killer of closed terrariums.
The Real Goal: Equilibrium, Not Perfection
You’re not trying to build a perfect system on day one. You’re tuning moisture levels until condensation forms on the glass in the morning only, then clears by afternoon. That rhythm tells you water is cycling properly.
The glass is your diagnostic tool. Clear afternoons mean balanced cycling. Foggy all day means too much water trapped inside. Bone dry glass means you’ve ventilated too much and need to add moisture back.
Mississippi State Extension recommends an open-close rhythm after assembly. Crack the lid for a few hours, then seal it again. Repeat daily until the fog pattern stabilizes into mornings only. That’s when you know you’ve found your jar’s equilibrium.
Layer One: The Reservoir That Saves Your Roots
LECA vs Gravel: The Material Choice That Actually Matters
LECA stands for lightweight expanded clay aggregate. It’s those tan porous balls you see at garden centers. Each ball is basically a ceramic sponge, full of tiny air pockets that absorb and release moisture gradually.
I switched from gravel to LECA three years ago and haven’t looked back. LECA wicks moisture upward through capillary action, which means your substrate stays evenly moist instead of bone dry on top and swampy below. River stones just sit there. They’re heavy, they don’t move water, and if you’re using a glass container, all that weight stresses the bottom.
Aquarium gravel can work, but check the coating. Some types leach chemicals that harm sensitive tropical plants. If you’re using gravel, rinse it thoroughly and stick with natural river rock.
| Material | Weight | Water Movement | Cost | Best For |
|---|---|---|---|---|
| LECA | Light | Wicks moisture up | Moderate | Long-term closed systems |
| River stones | Heavy | Passive only | Low | Large containers with strong bases |
| Aquarium gravel | Medium | Minimal | Low | Temporary or open terrariums |
| Perlite | Very light | Floats when wet | Low | Avoid for drainage layer |
How Deep Should You Really Go?
Target one to two inches for most jars. If you’re working with a tall apothecary jar (12 inches or more), you can go deeper. For small fishbowls under six inches tall, stick to one inch maximum or skip the drainage layer entirely and use a highly aerated substrate instead.
Here’s the math I use. For every inch of terrarium height, allocate roughly 15 percent to drainage. A six-inch jar gets about one inch of LECA. A ten-inch jar can handle 1.5 inches comfortably.
Deeper reservoirs waste precious root space. Your plants need room to grow down, and substrate depth matters more than drainage depth for long-term health. Too shallow offers no protection buffer when you accidentally add too much water during a misting session.
You should see distinct pebbles or clay balls when you look through the glass, not a compressed solid mass. If your drainage layer looks dense and packed, you’ve added too much or chosen the wrong material.
The False Bottom Isn’t Drainage, It’s Insurance
Let me reframe how you think about this layer. In open pots, drainage means water leaves the container entirely. In closed jars, drainage means water waits in a reservoir at the bottom while your plants use what they need from the substrate above.
This layer catches accidental overwatering so roots don’t sit directly in puddles. It’s a waiting room for moisture cycling back up through evaporation and capillary action. Roots breathe in the substrate while excess water sits patiently below, ready to re-enter the cycle when humidity drops.
Think of it as insurance against your worst misting mistake. You’ll make one eventually. We all do. That false bottom gives you a buffer zone where water can hang out harmlessly instead of drowning your nerve plants.
Layer Two: The Barrier Nobody Remembers (Until It’s Too Late)
Why Your Beautiful Layers Will Turn to Mud Without This
I’ve seen this happen to at least a dozen terrariums built by friends who skipped the barrier. At first, everything looks perfect. Clean layers, happy plants, beautiful glass walls. Then around month four or five, the drainage layer starts looking brown instead of tan. By month six, it’s completely clogged with fine soil particles.
Here’s what’s happening. Soil particles are tiny. They sift down through gaps in your LECA or gravel every time water cycles through the system. This happens slowly over months, then suddenly your reservoir is brown sludge with zero air pockets. Roots can’t breathe. Water can’t move. Everything suffocates.
The barrier is like the foundation in a house keeping rooms separate. Without it, your basement floods into your first floor, and the whole structure fails.
Mesh or Moss: Pick Your Separation Strategy
You’ve got two good options here, and your choice depends on how long you want this terrarium to last.
Landscape fabric or fine mesh (the kind used for screen doors) lasts forever and stays invisible through glass. Cut a piece slightly larger than your container’s diameter. It won’t break down, won’t compress, and you’ll forget it’s even there. For long-term closed terrariums you want to run for years, mesh wins every time.
Dried sphagnum moss is natural, looks beautiful layered between drainage and substrate, and works perfectly fine if you plan to refresh your terrarium annually. But it compresses over time, especially under the weight of wet substrate. After 12 to 18 months, it’s a thin mat instead of a fluffy barrier, and soil starts sneaking through.
I use mesh in terrariums I’m building to last. I use moss in seasonal builds or when aesthetics through clear glass matter more than maximum longevity.
Installation That Actually Keeps Soil Separated
Cut your mesh slightly larger than your container’s base diameter. You want edges that curl up the walls about half an inch. No gaps allowed, especially around the edges where glass meets drainage layer.
If you’re using moss, rehydrate it first until it’s damp and pliable, then press it down firmly in an even layer. Check through the glass from the side. Can you see any gaps where soil might sift through? Fill them now before substrate goes in.
One trick I learned from a vivarium builder in Portland: after placing mesh, add a thin dusting of sphagnum moss on top of it. The moss catches the finest particles that might squeeze through mesh holes, and it gives beneficial bacteria a textured surface to colonize. Best of both worlds.
Layer Three: Charcoal, The Misunderstood Filter
What It Actually Does (And Doesn’t Do)
Activated charcoal has microscopic pores covering every surface. When water passes through during your terrarium’s condensation cycle, those pores trap impurity molecules, organic compounds, and bacteria. It literally filters the water that’s recycling through your closed system.
It also absorbs odors. That sweet earthy smell you want in a healthy terrarium? Charcoal helps maintain it by grabbing the compounds that cause sour, swampy smells when organic matter breaks down.
But here’s the reality check. Charcoal won’t fix overwatering. It won’t save wrong plant choices. It can’t compensate for zero drainage or compacted substrate. It supports a healthy system; it doesn’t rescue a failing one.
Activated vs BBQ: The Difference That Keeps Jars Fresh
You need activated charcoal, also called horticultural charcoal. It’s been heated to extreme temperatures that create all those microscopic pores. One gram of activated charcoal has a surface area of roughly 3,000 square meters when you account for all the internal pore space. That’s nearly three-quarters of a football field of filtration packed into something the size of a marble.
BBQ charcoal is dense and useless for terrariums. It’s designed to burn slowly, not filter water. And never, ever use charcoal briquettes with lighter fluid additives. That stuff is toxic to delicate tropical plants.
A small bag of activated charcoal lasts years. I bought a two-pound bag in 2021 and I’m still working through it. Don’t cheap out and grab whatever’s at the hardware store. Spend the extra five dollars on actual horticultural charcoal from a garden center or online.
How Much Is Actually Enough?
Target half an inch of charcoal, just enough to dust the barrier layer. You want a thin, even coating visible through the glass as a dark stripe. More doesn’t help because charcoal doesn’t hold water like substrate does. It filters what passes through, then lets it continue moving.
I’ve tested this with side-by-side terrariums. One with a quarter-inch of charcoal, one with a full inch. No measurable difference in plant health or water clarity after six months. The thicker layer just wasted space I could’ve given to substrate and roots.
Pour charcoal gently, tilted against the inside glass to prevent black dust clouds. Those clouds settle everywhere and make your previously clean layers look muddy. If you do create a dust storm, wait for it to settle completely before adding substrate, then brush glass walls clean with a soft paintbrush.
Layer Four: The Soil Mix That Breathes in Humidity
Why Regular Potting Soil Is Slowly Killing Your Plants
I used to grab whatever potting soil was on sale at the big box store. Worked fine for my houseplants in regular pots. Killed every closed terrarium I built within three months.
Standard potting mixes are designed for containers with drainage holes. They expect water to flow out the bottom, carrying away excess moisture and maintaining air pockets through gravity drainage. In a sealed jar, that never happens. The mix stays constantly humid. It compacts under its own weight, squeezing out air pockets. Roots suffocate even though the soil looks moist and healthy.
Too much fertilizer causes explosive growth in a space with nowhere to expand. Your fittonia doubles in size in two months and chokes out everything else. Then it runs out of room, starts touching glass, and rots where condensation stays trapped against leaves.
Garden soil brings hitchhiking pests and pathogens into your sealed ecosystem. Fungus gnat larvae, soil mites, mold spores waiting for humid conditions. You’re creating a perfect incubator for every problem that soil was already carrying.
The Three-Part Formula for Tropical Closed Terrariums
This is the substrate recipe I use for 90 percent of my closed terrariums. It mimics the ABG mix (Atlanta Botanical Garden mix) developed for bioactive vivariums, but simplified for beginners.
Two parts coconut coir holds moisture like a sponge without turning soggy. It’s made from coconut husk fibers, so it resists breakdown in high humidity. Water retention capacity is excellent, but it doesn’t stay waterlogged.
One part orchid bark creates air channels throughout the substrate. Even when compressed, bark chunks maintain gaps where oxygen reaches roots. It resists decomposition for years in humid conditions.
One part perlite or coarse sand prevents compaction and adds drainage structure throughout the mix. I prefer perlite because it’s lighter and doesn’t settle to the bottom over time like sand does.
Basic Closed Terrarium Substrate Recipe:
- 2 parts coconut coir (pre-moistened, then squeezed out)
- 1 part orchid bark (medium size chunks, not fine dust)
- 1 part perlite (horticultural grade, not construction perlite)
- Optional: handful of sphagnum moss mixed in for extra moisture buffering
For moss-only terrariums, skip this entirely and use pure sphagnum or a 50/50 mix of sphagnum and coconut coir. Moss doesn’t need complex substrate since it absorbs moisture directly through its leaves.
The Squeeze Test That Tells You Everything
Before substrate goes anywhere near your terrarium, mix it thoroughly in a bowl and run this test. It’ll save you from having to rebuild everything in two months.
Grab a handful of your mixed substrate and squeeze it as tight as you can. Really crush it in your fist. Now open your hand and watch what happens.
The mix should clump lightly, holding its shape for a second or two. Then it should crumble apart into loose chunks when you poke it. If it stays in a solid muddy ball, you’ve got too much water-retentive material. Add more orchid bark and perlite immediately. If it won’t clump at all and feels dusty dry, add a bit more coir or a splash of water.
This test tells you if your substrate will maintain air pockets under the constant humidity of a closed system. Substrate that clumps into mud today will compact into an airless brick in six months.
How Deep to Make This Living Layer
Give roots at least two to three inches of substrate depth. Ferns, nerve plants, and anything with a substantial root ball needs the full three inches. Small mosses and creeping fig can work with two inches, but deeper is always safer.
I like to slope substrate from front to back, creating depth perspective. Maybe two inches at the front glass wall, three or even four inches at the back. This gives visual interest and accommodates plants with different root depths in the same container.
Substrate Depth by Plant Type:
| Plant Type | Minimum Depth | Ideal Depth | Notes |
|---|---|---|---|
| Sheet moss, cushion moss | 1 inch | 1-2 inches | Roots are minimal, needs moisture contact |
| Creeping fig, pilea | 2 inches | 2-3 inches | Shallow roots, moderate feeders |
| Fittonia, nerve plants | 2.5 inches | 3-4 inches | Vigorous roots, appreciates depth |
| Ferns (small varieties) | 3 inches | 3-5 inches | Deep root systems, nutrient hungry |
| Trailing vines (pothos) | 2 inches | 3-4 inches | Roots spread laterally, depth helps stability |
Remember, these depths are for the substrate layer only, on top of your drainage and charcoal. A six-inch tall container with one inch LECA, half-inch charcoal, and three inches substrate leaves about 1.5 inches of headroom for plants and air circulation. That’s perfect.
Building the Layers Without Turning Them to Soup
Before You Start: Container Prep That Prevents Disaster
Wash your glass container with hot soapy water. I mean really scrub it. Oil residues from manufacturing, dust from storage, fingerprints from handling—all of this can poison delicate tropical plants or create spots where algae colonizes in your closed system.
Rinse thoroughly until water runs clear with zero soap bubbles. Then rinse again. Then rinse once more.
Dry the container completely. I leave mine upside down on a towel overnight. Any moisture you start with throws off your equilibrium tuning later because you don’t know how much water is actually in the system. Start with bone-dry glass so you can control every drop you add.
Gather all your materials within arm’s reach before you start layering. LECA in one bowl, charcoal in another, substrate mixed and ready, mesh cut to size, plants still in their nursery pots nearby. Once you start building, you don’t want to be hunting for supplies with dirty hands and half-finished layers sitting exposed.
The Pour Sequence for Clean, Visible Layers
Use a funnel or a rolled piece of paper to pour LECA down the inside wall of your container. This keeps the center empty and glass sides clean. Pour slowly, watching the clay balls roll into place. Distribute evenly by tilting and rotating the container, not by sticking your hand inside and shoving things around.
For mesh barrier, I roll it into a loose tube, lower it into the container vertically, then unroll it flat once it’s resting on the LECA. This keeps it from sliding around or bunching up. Smooth it gently with the back of a spoon through the top opening.
Sprinkle charcoal next, tilted against the glass to prevent black dust clouds. Pour a bit, rotate container, pour more, rotate again. You want even coverage, not a pile in one spot. A soft paintbrush is your best friend here for cleaning glass walls between layers.
Add substrate in small batches. A few spoonfuls at a time, tamping lightly with the back of a long spoon to remove large air pockets but not compacting it into cement. I like to build up the back higher than the front as I go, creating that sloped perspective.
The Critical Mistake: Mixing Layers During Assembly
Last month, a friend showed me her terrarium that looked like a muddy mess after just three weeks. The LECA layer was streaked with brown and black instead of clean tan. Charcoal dust had migrated everywhere. She’d poured everything too fast without cleaning between layers.
Here’s what happens. Charcoal dust is incredibly fine. If you dump substrate on top before that dust settles, substrate particles mix with charcoal, which then sifts down into your LECA during the first watering cycle. Your drainage layer turns into muddy sludge that can’t drain or breathe.
If you see black streaks on your LECA after adding charcoal, stop. Gently lift the mesh barrier and shake excess dust off the top. Use a brush to clean glass walls. Wait five minutes for remaining dust to settle, then proceed.
Clean glass sides with a soft brush after each layer before adding the next. You can’t fix this once substrate goes in without completely rebuilding. Taking two extra minutes between layers saves you from tearing everything apart in a month.
Tuning Moisture: Where Most Guides Stop (And Where Success Starts)
The First Misting: Less Than You Want, Always
Your substrate should be lightly moist when it goes into the container. Not dripping wet. Not bone dry. Think of a wrung-out sponge. When you squeeze substrate in your hand, it should feel cool and damp but not release any liquid.
After planting, you’ll probably need to add a bit more water. Use a misting bottle, not a watering can. A few spritzes on the substrate surface and inner glass walls. That’s it. Seal the lid and walk away.
You can add water tomorrow if needed. You cannot easily drain a flooded sealed jar. In closed systems, less is always, always safer than more at the start. I’ve salvaged dozens of too-dry terrariums by adding water gradually. I’ve never successfully saved a flooded one without completely rebuilding.
The Equilibrium Routine That Prevents Fog Forever
This is the part that separates beautiful terrariums from swampy disasters. You’re going to actively tune moisture levels for the first two weeks until your system finds its balance point.
Day one: Leave the lid completely off for 24 hours. This lets initial excess moisture evaporate from substrate and glass.
Day two: Close the lid. Check in the evening. Is the glass completely fogged over, impossible to see through? That’s too much moisture.
Day three: If foggy, open the lid for several hours. If already clearing by afternoon, keep it closed.
Repeat this open-close rhythm daily, adjusting the length of time you vent based on what the glass tells you. You’re looking for a pattern where condensation forms overnight and in early morning, then clears by afternoon. That’s the sweet spot.
When you hit three consecutive days with this pattern, stop venting. Your terrarium has found equilibrium. It should maintain that rhythm indefinitely without intervention.
Reading the Warning Signs Before Plants Suffer
Your nose is a diagnostic tool. A healthy closed terrarium smells sweet and earthy, like a forest floor after rain. Stick your nose near the opening when you crack the lid to vent. If you smell anything sour, musty, or like rotting vegetation, you’ve got too much stagnant water and anaerobic bacteria are having a party.
Foggy mornings are completely normal and healthy. That’s your water cycle working perfectly. Foggy afternoons mean you need to vent now. Open that lid for a few hours and let excess moisture escape.
Look at the soil surface. If it’s glossy wet, almost muddy looking, you’re oversaturated. Crack the lid and leave it open until the surface looks moist but not shiny. If you see water beading on the substrate surface, you’ve flooded it. Open immediately and vent for a full day.
The most reliable indicator is condensation behavior. Water droplets should form on glass overnight, then gradually evaporate as the day warms. If droplets are running down glass constantly, that’s excessive. If glass stays bone dry even in the morning, you need to add moisture.
When Layers Go Wrong: Troubleshooting Without Starting Over
Recognizing Drainage Layer Failure Early
You’ll see this before your plants show symptoms if you’re checking through the glass regularly. Water pooling visibly at the bottom that never evaporates back up. The LECA or gravel layer looks darker, almost muddy instead of clean and distinct.
Substrate stays soggy for days after a light misting. Normally, closed terrariums reach equilibrium where substrate stays evenly moist, not wet. If you’re seeing waterlogged soil that doesn’t dry out even with the lid cracked open, your drainage is clogged or you’ve simply added too much water for the system to cycle.
The smell test catches this early. Crack the lid and take a deep breath. Healthy terrariums smell like rich earth and green growing things. A foul swamp smell, like stagnant pond water, screams anaerobic bacteria. That happens when drainage fails and water sits stagnant with zero oxygen exchange.
Drainage Failure Checklist:
- Visible standing water at bottom of container
- Substrate waterlogged for 3+ days after misting
- Foul or sour smell when lid is opened
- LECA layer appears brown or muddy instead of clean
- Plants yellowing from bottom up (root rot symptoms)
The Soggy Soil Crisis and How to Fix It
First step: open that lid and leave it open. Not just cracked, fully removed. Give your system several hours of air exchange daily until moisture levels visibly drop.
If you can see standing water in the drainage layer, carefully tilt the entire container to drain excess into a shallow dish. Do this slowly. You’re trying to remove the free water without disturbing your plants or mixing up your layers.
Sometimes you catch this early enough that extended venting is all you need. Other times, you need to know when to rebuild. If your plants are already yellowing and the smell is strong even after a week of venting, it’s usually faster to start fresh than to try nursing a waterlogged system back to health.
I’ve tried to save soggy terrariums by adding springtails (tiny clean-up crew insects) to process excess moisture. It works sometimes, but only if the overwatering is mild. If you’re seeing black mushy roots when you gently tug a plant, it’s too late. Harvest any healthy plant cuttings and rebuild with less water this time.
White Mold on Soil: Panic or Normal?
The first time you see fuzzy white mold spreading across your substrate surface, it’s alarming. I get it. But here’s the thing: surface mold is incredibly common in new terrarium builds and it’s usually harmless.
When you seal a container, you’re trapping microorganisms that were already present in your substrate, on your plants, even in the air. Those microbes settle in and start colonizing surfaces. White fuzzy mold is often saprophytic fungi breaking down organic matter. It’s part of the ecosystem establishing itself.
Wipe it away gently with a damp paper towel or cotton swab. Don’t scrape aggressively or you’ll disturb substrate and damage shallow roots. Then increase air circulation for a full week. Crack the lid for a few hours daily. This usually stops the mold from returning.
Mold on the soil surface is different from black rot in the substrate. Surface mold is cosmetic and temporary. Black mushy roots or substrate that’s turned dark and slimy means you’ve got serious rot and need to intervene aggressively.
If mold keeps coming back even with venting and you’re tired of fighting it, add a clean-up crew. Springtails and isopods (tiny beneficial insects) eat mold, dead plant matter, and excess bacteria. They’re the janitors of closed ecosystems. For more information on maintaining a healthy closed terrarium ecosystem, check out Penn State Extension’s guide to creating closed terrariums, which offers research-backed insights on substrate selection and moisture management.
Conclusion: The Foundation That Changes Everything
You started this wanting a beautiful jar and ended up learning something deeper: that plants don’t just need soil, they need architecture. A reservoir that protects roots. A barrier that keeps zones separate. A filter that refreshes recycled water. A substrate that breathes even when air is thick with humidity. These aren’t steps in a Pinterest craft; they’re the engineering of a tiny, self-sustaining world.
Think about where you were at the start. Confused about why your last terrarium failed. Overwhelmed by conflicting advice about drainage layers, charcoal, and substrate depth. Now you understand that the layers work together as a system, and tuning that system through moisture equilibrium is where the magic actually happens.
The jar you’re about to build won’t fail because of mystery problems. If something goes wrong, you’ll know exactly which layer isn’t functioning and how to fix it. You’ll read the condensation pattern on glass and adjust before plants suffer. You’ll recognize the difference between healthy surface mold and dangerous root rot.
Before you touch a single plant, mix your substrate in a bowl and run the squeeze test. Grab a handful, squeeze it tight, then watch it crumble in your palm. That single moment of getting the texture right is where thriving begins, before anything even enters the jar. If it clumps like mud, add orchid bark and perlite until it breathes freely. That’s your foundation.
You’re not bad at terrariums. You just needed someone to explain the parts that actually matter. Now go build a foundation that lasts. Your miniature rainforest is waiting.
Closed Terrarium Layers Guide (FAQs)
Do I need activated charcoal in a closed terrarium?
Yes, activated charcoal filters recycled water and absorbs odors as moisture cycles. Half an inch is enough. It won’t save a poorly built system but supports healthy ones by trapping bacteria and organic compounds. Horticultural charcoal works; BBQ charcoal doesn’t because it lacks the porous structure needed for filtration.
What is the correct order for terrarium layers?
Start with drainage (LECA or gravel), add barrier mesh or moss, sprinkle charcoal, then substrate on top. This bottom-to-top sequence keeps layers separate and lets water cycle properly. Never mix layers during assembly or you’ll clog the drainage system with fine particles that suffocate roots.
How thick should each terrarium layer be?
Target 1 to 2 inches for drainage, half an inch for charcoal, and 2 to 3 inches for substrate in standard jars. Scale proportionally to container height. Small containers under six inches tall can skip drainage entirely if you use aerated substrate and water carefully.
Can I use perlite instead of LECA for drainage?
No, perlite floats when wet and clogs drainage. LECA stays put, wicks moisture upward through capillary action, and maintains air pockets under substrate weight. River stones work but add weight. For closed systems lasting years, LECA outperforms all alternatives because it actively moves water instead of just creating empty space.
What happens if substrate is too deep in a closed terrarium?
Too much substrate wastes headroom plants need to grow upward and restricts air circulation. It also extends the time needed to reach moisture equilibrium because you’re cycling more water. Keep substrate at 2 to 3 inches for most plants. Ferns can use up to 4 inches if your container is tall enough to accommodate it.