How to Build a Terrarium: The No-BS Guide to Growing a Tiny World in a Jar

So you want to build a terrarium.

Maybe you saw one on Instagram and thought, “I could totally do that.” Maybe your apartment is so dry that regular houseplants stage a protest and die within two weeks. Or maybe you just like the idea of playing god over a tiny ecosystem that fits on your coffee table.

Whatever your reason, you’re in the right place.

Building a terrarium is one of those rare projects that’s actually as fun as it looks, takes less than an hour, and practically takes care of itself afterward. I’m talking about a living, breathing mini-jungle that waters itself and just… works.

Let me walk you through the whole thing.

First Things First: Open or Closed?

Before you grab any supplies, you need to make one big decision.

Open terrariums have no lid. They’re drier, need more watering, and work best for succulents and cacti that hate humidity.

Closed terrariums are sealed (or mostly sealed). They trap moisture, recycle it, and create their own little water cycle. Think of it like a tiny tropical rainforest in a jar.

Here’s the deal: if you want that classic, lush, green-on-green terrarium look that basically runs itself, go closed. That’s what we’re focusing on today.

A closed terrarium recycles water through evaporation and condensation, essentially watering itself over and over. You set it up, give it one good drink, seal the lid, and it can go months (sometimes years) without needing a single thing from you.

That’s not lazy gardening. That’s smart gardening.

Picking Your Container

Almost any clear glass container can work.

Mason jars, old cookie jars, fish bowls, apothecary jars, that weird vase you got as a wedding gift and never used — all fair game.

The one rule? The wider the opening, the easier your life will be. Trying to arrange tiny plants through a narrow bottle neck is like performing surgery with oven mitts on. Start with something you can comfortably fit your hand into.

You can find great containers at thrift stores for a couple bucks. No need to drop $40 on a fancy terrarium vessel when a $3 cookie jar from Goodwill does the exact same job.

If your container doesn’t have a lid, don’t panic. A glass plate, a piece of acrylic, or even plastic wrap works as a temporary seal.

The Shopping List

Here’s everything you need. Most of it costs less than a fast food meal.

Material	Purpose	How Much
Small pebbles or LECA balls	Drainage layer	2-3 cm deep
Activated charcoal	Filters water, fights bacteria and odors	A thin sprinkle (1 tablespoon is plenty)
Sphagnum moss	Barrier layer to keep soil from sinking into the rocks	Thin layer
Potting soil (or ABG mix)	Where your plants actually live	5-7 cm deep
Tropical plants (2-4 small ones)	The whole point of this operation	Varies by container size
Spray bottle	For watering	One good misting
Decorations (optional)	Rocks, figurines, driftwood, crystals	Whatever makes you happy

Pro tip: If you can find ABG (Atlanta Botanical Garden) mix instead of regular potting soil, grab it. It’s specifically designed for terrarium use and reduces mold issues by a huge margin compared to generic potting soil. It costs a few bucks more. It’s worth every penny.

The Best Plants for Beginners

This is where people mess up the most.

They grab whatever looks pretty at the garden center without checking if it actually belongs in a humid, enclosed environment. Then two weeks later, everything’s rotting.

Do not put succulents or cacti in a closed terrarium. They will absolutely hate you for it. Those plants want dry, airy conditions. A sealed glass jar (the jar I built my jarrarium in) is basically their worst nightmare.

For a closed terrarium, stick to tropical plants that love moisture and humidity.

Here are the ones that almost never fail:

Plant	Why It Works	Vibe
Fittonia (Nerve Plant)	Loves humidity, comes in pink, white, and green varieties	Colorful ground cover
Ferns (Lemon Button, Maidenhair)	Thrive in high humidity, gorgeous texture	Lush and elegant
Peperomia	Hardy, compact, tons of varieties	Reliable workhorse
Polka Dot Plant (Hypoestes)	Spotted leaves, does great in humid setups	Fun and playful
Ficus pumila (Creeping Fig)	Tiny vine that fills in gaps beautifully	Natural crawling accent
Pilea (Aluminum Plant, Moon Valley)	Compact, interesting leaf texture	Subtle stunner
Selaginella (Clubmoss)	Low-growing, spreads like a green carpet	Forest floor feel

The golden rule: Pick slow growers. A plant that grows fast in a terrarium will take over everything in a month and choke out its neighbors. You’re building a balanced ecosystem, not hosting a plant battle royale. For a complete breakdown of all your plant options by terrarium type, see our guide to terrarium plants.

How to Build It: Step by Step

Alright, here’s where we get our hands dirty. Literally.

Step 1: Clean Your Container

Wash your glass container with hot water and wipe it down. Some people use a little isopropyl alcohol to kill any lurking fungal spores.

This step sounds boring. It prevents roughly 1 out of every 5 beginner terrariums from getting wrecked by mold in the first month. Do it.

Step 2: Add the Drainage Layer

Pour in your pebbles or LECA balls. Aim for about 2-3 cm thick at the bottom.

This layer is non-negotiable. Your terrarium has no drainage holes, so water needs somewhere to go that isn’t sitting around your plant roots. Without this layer, you’re basically building a swamp.

Step 3: Sprinkle in the Charcoal

Add a thin layer of activated charcoal on top of the pebbles. About one tablespoon for a standard jar-sized terrarium.

Activated charcoal acts like a natural water filter. It absorbs toxins, fights bacteria, and keeps your terrarium from developing that funky swamp smell nobody wants.

Don’t go overboard here. More charcoal doesn’t mean better results. Testing has shown that a small amount actually works better than a thick layer because excess charcoal can mess with moisture balance.

Step 4: Add the Moss Barrier

Lay a thin layer of sphagnum moss over the charcoal.

This does two things. It stops your soil from gradually sinking down into the drainage layer (which would defeat the whole purpose). And sphagnum moss can hold up to 25 times its weight in water, so it acts like a humidity buffer for your plants.

Tease the moss apart with your fingers to fluff it up and spread it evenly. For build ideas centered entirely around moss, these moss terrarium ideas show what’s possible when you lean into it.

Step 5: Add Your Soil

Pour in your potting soil or ABG mix. You want enough depth for your plant roots to sit comfortably — usually around 5-7 cm.

Pack it gently. You want it firm enough to hold plants in place but not so dense that water can’t flow through it. No air pockets, but no concrete either.

Step 6: Plant Your Plants

Now the fun part.

Start with your tallest plant first and work toward the smallest. This helps you gauge the scale and create natural-looking layers.

Remove each plant from its nursery pot, gently loosen the root ball, and make a small hole in the soil. Nestle it in, press the soil around the base, and move on to the next one.

Leave about 2 cm between each plant. They’re going to grow. Give them room.

A few design tips that make a big difference:

• Put your tallest plant toward the back (or center if the terrarium is viewed from all sides)
• Use trailing plants near the edges so they cascade naturally
• Create depth by varying heights — tall, medium, low

Step 7: Add Decorations

This is optional, but it’s also the part that takes your terrarium from “nice” to “wow.”

Small rocks, pieces of driftwood, crystals, seashells, even tiny figurines. Whatever tells a story. For a full breakdown of decor styles and themes, our terrarium decor ideas guide goes much deeper.

Just make sure you wash anything you put in there first. Unwashed decorations can introduce bacteria or pests.

Step 8: Water and Seal

Give your terrarium a light misting with a spray bottle. You want the soil damp, not soaked. Think “morning dew,” not “monsoon season.”

Seal the lid and watch what happens.

Over the next 24-48 hours, you should see some condensation form on the glass. A little fog is perfect. That means the water cycle is doing its thing.

If the glass is completely fogged up and you can’t see your plants, you’ve added too much water. Pop the lid off for a few hours to let some moisture escape, then seal it again.

If there’s zero condensation after a day, add a few more sprays and try again.

Where to Put Your Terrarium

This one trips up a lot of people.

Never put your terrarium in direct sunlight. I know it seems logical. Plants need sun, right? But glass acts like a magnifying lens. Direct sunlight will turn your terrarium into a tiny oven and cook your plants alive.

Bright, indirect light is the sweet spot. A spot in a well-lit room where you could comfortably read a book, but you wouldn’t feel the sun’s warmth on your skin.

Also keep it away from radiators, heat vents, and the top of your fridge. Any heat source can mess with the internal temperature and throw off the moisture balance.

The Secret Weapon: Springtails

Here’s something most beginner guides won’t tell you about.

Springtails are tiny insects (1-6 mm) that eat mold, fungi, and decaying plant matter. They’re basically a self-sustaining janitorial crew for your terrarium.

Mold is the number one terrarium killer for beginners. You see a patch of white fuzz on your soil and panic. Springtails prevent that problem almost entirely.

They eat the mold before it spreads. They break down dead leaves before they rot. They aerate the soil by tunneling through it. And they release nutrients back into the substrate as they work, which actually helps your plants grow better.

A single starter culture (you can buy them online for a few dollars) is all you need. Drop them in, and they’ll reproduce on their own. Their population self-regulates — they only breed as fast as their food supply allows, so they never overpopulate.

Springtails are so effective that experienced terrarium builders consider them essential, not optional. If you’re serious about your terrarium lasting more than a few months, add them.

Common Mistakes That Kill Terrariums

Let’s save you some heartbreak.

Mistake	What Happens	The Fix
Overwatering	Root rot, mold explosions, swampy mess	Use a spray bottle, not a watering can. Less is more.
Direct sunlight	Plants scorch, temperatures spike	Bright indirect light only
Wrong plants	Succulents rot in humidity, tropicals dry out in open air	Match plants to terrarium type
Skipping charcoal	Stagnant water, bacterial growth, bad smell	Always include a charcoal layer
Overcrowding	Plants compete for light and space, weaker ones die	2-4 plants max for a standard jar
Using garden soil	Too dense, may contain pests and pathogens	Use terrarium-specific or indoor potting mix
Ignoring dead leaves	Decay spreads, mold blooms	Remove dead plant material immediately
No drainage layer	Waterlogged roots, plant death	Pebbles or LECA at the bottom, always

Maintenance: It’s Almost Nothing

This is the best part about closed terrariums.

Once you nail the moisture balance, your maintenance checklist looks like this:

• Weekly: Quick visual check. Look for yellowing leaves, mold patches, or anything that looks off. Takes about 30 seconds.
• Monthly: Clean the glass inside and out with a damp lint-free cloth. Trim any plants that are getting too big. Remove dead leaves.
• Every few months: Check if the soil looks dry (no condensation on the glass). If so, give it a few spritzes of water.

That’s it. That’s the whole routine.

Some closed terrariums have gone years without being opened or watered. The oldest known sealed terrarium was planted by David Latimer in 1960 and thrived for over 50 years without being watered after 1972.

Your terrarium probably won’t last 50 years. But it can definitely outlast most relationships with houseplants.

The Budget Breakdown

You don’t need to spend a lot.

Item	Estimated Cost
Glass container (thrift store)	$2-5
Pebbles/LECA	$3-5
Activated charcoal	$3-5
Sphagnum moss	$3-5
Potting soil or ABG mix	$5-10
2-4 small plants	$8-15
Spray bottle	$1-2
Springtails (optional but recommended)	$5-10
Total	$30-57

That’s less than most people spend on a single restaurant dinner. And this thing lasts for years.

Quick Recap

Let’s run it back fast:

1. Pick a clear glass container with a wide opening
2. Layer it up: pebbles, charcoal, moss, soil
3. Choose tropical plants that love humidity
4. Plant from tallest to smallest, leave space between them
5. Mist lightly, seal the lid, and place in bright indirect light
6. Add springtails for mold prevention
7. Do almost nothing forever

Go Build One Already

Look, I could keep talking about terrariums all day. But the best way to learn is to just build one.

Your first one might not be perfect. You might overwater it. You might pick a plant that doesn’t work out. That’s fine. That’s how literally everyone starts.

The materials are cheap, the time investment is tiny, and even a “failed” terrarium teaches you exactly what to do differently next time.

So grab a jar, hit up your local garden center, and start layering. Your future self — the one who has a living, self-sustaining miniature jungle on their desk — will thank you.