How to Make a Terrarium: A Complete Beginner's Guide

I do not, as a rule, believe in the idea that the more you put into something the more you get out of it. That has not been my experience with relationships, home improvement, or any recipe that requires a mandoline. But a terrarium is the exception. A terrarium built well is a tiny ecosystem that runs on its own terms, and looking at one you made yourself produces a feeling I can only describe as monarchic — a king surveying his village from the window, satisfied, proprietary, certain that he is responsible for everything happening down there, right up until the queen walks in and hits him in the back of the head for standing around doing nothing.

How do you make a terrarium?

To make a terrarium, layer a glass container from the bottom up: a drainage layer of pebbles, a thin layer of charcoal, then potting soil, and finally your plants. For a closed terrarium, seal the lid and the sealed environment recycles its own moisture — condensation forms, runs back down, and the system waters itself. For an open one, you water occasionally. The build is the same; the lid is the difference.

A true terrarium is a group of plants sealed inside glass that you never open and never water again, which sounds like neglect but is in fact the entire point. You close the lid, you walk away, and then deeply strange things start happening in there without your permission. Condensation appears. Moisture recirculates. The plants develop a private economy among themselves that does not include you, did not consult you, and will continue long after you have stopped checking. It is the most unsettling beautiful thing you can put on a shelf. What most people actually own is an open glass vessel with some nice plants in it, which is also beautiful but will not develop its own weather system or make you feel briefly, unexpectedly, like God on the eighth day when he'd already clocked out.

What do you need to build a terrarium?

You need a glass container, drainage material (pebbles or gravel), activated charcoal, potting soil, and small plants. The layers go bottom to top: about an inch of pebbles for drainage, a thin layer of charcoal, then two to three inches of light potting soil. University of Vermont Extension recommends exactly this order — gravel for drainage (since the container has none), a thin charcoal layer to prevent odors and bacteria, then light soil.

Pebbles. Charcoal. Soil. In that order, and I need you to understand that you are not making a craft project, you are building a small sewage system for plants, which is less romantic but entirely more useful as a mental model. The pebbles are the drainage — water falls through, collects at the bottom, and does not sit against the roots pretending to be helpful while it drowns them. The charcoal filters the water so the whole arrangement does not start smelling like a swamp that has developed a grudge by week three. The soil is where the plant lives. Parking garage, mechanical room, apartment. Every layer exists because the layer above it will fail without it. Skip the charcoal because you read somewhere it's optional and a glass terrarium in six weeks will show you exactly why it was not.

What's the difference between an open and a closed terrarium?

A closed terrarium has a lid and recycles its own moisture, so once it's balanced it needs almost no watering — sometimes none for months. An open terrarium has no lid, loses moisture to the air, and needs regular watering like a normal potted plant. Closed suits humidity-loving plants; open suits plants that want their soil to dry out between waterings.

A closed terrarium is a negotiation that lasts about two weeks and then resolves itself permanently. You seal it. Condensation appears on the glass. You open it, let moisture escape, close it again. Too dry — you add a thimble of water and wait. You are having an argument with a closed system about humidity, and the closed system has stronger opinions than you do and more patience than you will ever have. Once the terms are settled — once the glass stays clear and the plants stop looking at you like you have done something wrong — you are finished. Forever. You never water it again. You never open it again. It is done with you. An open terrarium is a completely different relationship — pretty, accessible, and entirely dependent on you showing up with water on a regular basis like someone who has not yet earned the plant's trust. Both are worth having. One of them will eventually stop needing you, and whether that is a relief or an insult depends entirely on what you were looking for.

What plants are best for a terrarium?

Match the plant to the environment. Closed terrariums suit humidity-lovers — ferns, moss, fittonia, and, with the moisture kept in check, branching succulents. Open terrariums suit plants that want airflow and a chance to dry out, including carnivorous plants like flytraps and sundews. The one rule that never bends: every plant in one container has to want the same moisture level.

For closed terrariums I use small succulents with lots of branching, because once you seal the lid those things lose their minds in there. They grow sideways, they grow over each other, they grow with the unhinged energy of someone who has realized no one is watching and no one is coming in to intervene. It is the most entertaining thing on your shelf and it has been happening in total silence for months. For open terrariums, carnivorous plants — the whole murderous family. Pitcher plants. Sundews. The Venus flytrap your nephew will not stop asking about. These are plants that looked at photosynthesis and said no, I would also like to eat, and then built a mouth. A sealed glass jar with something that catches its own food is a fundamentally different object on a table than a glass bowl with a fern. One of them people walk past. The other one they stand over for four minutes asking questions you do not know the answer to.

How do you take care of a terrarium?

A closed terrarium in balance needs almost nothing — no watering for months, just leave it sealed. Missouri Extension notes a closed terrarium typically won't need water for four to six months; you only add water if condensation stops forming or plants wilt. For an open terrarium, keep a little water visible in the bottom drainage layer and add more when it disappears. The most common way to kill either one is doing too much, not too little.

One honest caveat, since I put branching succulents in a sealed jar earlier and someone always drowns one: closed succulents only work if you keep the moisture dialed down — damp, never wet — because a sealed jar traps humidity a desert plant did not ask for. Control the moisture and they thrive; ignore it and they rot. That is the one place a closed terrarium actually asks something of you. Everywhere else: if it is closed and the balance is right, you do nothing, and I need you to hear that as an instruction and not a dare. The system is working. Leave it alone. If it is open, look at the bottom layer through the glass — you should always be able to see a small amount of water sitting in the pebbles. If you see water, everything is fine. If you do not see water, add some. That is the entire job. I understand this does not feel like enough. I understand you want to mist something, rotate something, fuss over something that you spent forty-five minutes building and now feel responsible for. I need you to not do that. The thing that kills terrariums is not neglect and it is not bad light — it is the suffocating, well-meaning, absolutely relentless attention of a person who cannot accept that a living thing needs this little from them and is, in fact, doing better without their help.

Why is my terrarium dying?

The most common reason a terrarium dies is a plant mismatch: two plants with different water needs sharing one soil, so one is always wrong. Match every plant in a terrarium by watering needs — all humidity-lovers or all dry-lovers, never a mix. Penn State Extension sums up the whole principle as "right plant, right place." Overwatering and a heavy-drinker-next-to-a-non-drinker pairing kill more terrariums than bad light ever will.

You put a heavy drinker next to a non-drinker and expected them to coexist on one water supply, which has never once worked in any living arrangement at any scale in the entire history of sharing a space with another organism. One plant wants the soil wet. One plant wants the soil dry. They are in the same three inches of dirt. There is one moisture level and two completely incompatible expectations and someone has been quietly dying about it for weeks while you were looking at the one that seemed fine. Match your plants by watering needs. Not by color, not by what looked good together at the store, not by some Pinterest board that paired them based on the aesthetics of the photograph and not the biology of the actual plants in it. Roommate compatibility has never been about who looks nice next to whom. It is about who leaves the sink full of water and who does not, and if you get that wrong, one of them moves out. The plant version of moving out is dying, which is less dramatic but more permanent.

Whether you want the sealed kind that runs itself or the open kind you fuss over, the terrariums we make are built to show off the little world inside — including a mini terrarium for a first attempt.

Build the layers. Match the roommates. Seal the lid if you are brave enough to let something succeed without your constant involvement, or leave it open if you are not there yet. Either way, keep the heavy drinkers away from the non-drinkers, keep your hands off the closed one once the glass clears, and if you feel the urge to do more — the urge to mist, to water, to intervene in a system that is working fine without you — understand that the urge is the problem, and the terrarium already knows it.