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Plant Terrarium: Everything You Need to Know
From the basics to troubleshooting: this is the complete guide to plant terrariums, mini-ecosystems and bottle gardens - including answers to the questions most people search for online.
The basics
What is a plant terrarium?
A plant terrarium is a mini-ecosystem in glass: a pot, vase or bottle containing plants, soil and moisture that work together in a more or less closed cycle. Light enters through the glass, plants convert it into growth through photosynthesis, and the moisture they release condenses on the glass and drips back down to the soil. That's why a terrarium can go for weeks, sometimes months, with very little extra care.
What's the difference between an open and a closed terrarium?
A closed terrarium has a lid or cork and retains moisture almost completely, making it nearly self-sufficient — ideal for moisture-loving plants like ferns and fittonia. An open terrarium has no seal, loses moisture faster, and therefore needs watering more often. That makes open terrariums a better fit for drought-tolerant plants such as succulents and cacti.
What's the difference between a terrarium and a bottle garden?
In practice, they're two names for the same principle: plants growing in a (partly) enclosed glass environment. "Bottle garden" is traditionally used more for a planted bottle or large jar, while "terrarium" is the broader, more modern term that also covers geometric glass enclosures and ready-made kits. Functionally, both work in exactly the same way, through a natural water and air cycle.
Is a terrarium the same as a mini-ecosystem?
Yes, "mini-ecosystem" is essentially the technical description of what a terrarium does: a small-scale, largely self-sufficient system in which plants, soil life and moisture interact. Every closed plant terrarium is a mini-ecosystem, but not every mini-ecosystem has to be a terrarium — you'll also see the term used for things like planted aquariums without fish.
What are the advantages of a terrarium compared to regular houseplants?
A terrarium needs structurally less upkeep: thanks to the closed or semi-closed cycle, you have to water it far less often than a regular houseplant. It also creates a stable microclimate in which even more demanding, moisture-loving plants thrive, and gives you a decorative, self-contained patch of green that takes up little space and won't sprawl across your windowsill.
Building & layers
What do you need to build a terrarium?
The basics are: a glass pot, vase or bottle with an opening wide enough to fit plants through, drainage material (clay pebbles or gravel), activated charcoal, terrarium soil, suitable plants, moss, and optionally decoration like stones or twigs. A long pair of tweezers or a spoon is handy for placing everything neatly through a narrow opening.
How do you build a closed plant terrarium yourself?
Build up from the bottom: start with a drainage layer of clay pebbles or gravel, then a thin layer of activated charcoal, followed by terrarium soil, and place your plants and moss on top. Mist the whole thing lightly with water and leave the lid slightly ajar for the first week to let it acclimatize, before sealing it completely with the lid or cork.
How do you build an open terrarium with cacti or succulents?
Use the same drainage layer, but activated charcoal is often left out or used more sparingly, since an open terrarium naturally has fewer moisture issues. Use a coarser, fast-draining substrate (for example a mix with extra sand or perlite) instead of moisture-retaining terrarium soil, choose an open container or bowl without a lid, and place it somewhere bright. Only water once the soil has dried out completely.
Why do you need a drainage layer?
A layer of clay pebbles, pebbles or gravel at the bottom lets excess water drain away instead of pooling around the roots. Without it, water collects directly in the soil, which quickly leads to root rot and an unhealthy, oxygen-poor soil — especially in a closed terrarium, where the water has nowhere else to go.
Why do you need special terrarium soil, and can't you just use regular potting soil?
Regular potting soil is made for pots with drainage holes, where excess water can simply run off, and it's often enriched with fertilizer. In a sealed terrarium, that water has nowhere to go, so regular potting soil quickly becomes waterlogged, compacted and low in oxygen — a perfect breeding ground for root rot and mold. Terrarium soil has a lighter structure, holds moisture more evenly, and typically contains no added fertilizer, which makes it better suited to a closed, circulating system.
Why is activated charcoal used in a terrarium?
Activated charcoal has a hugely porous surface that filters pollutants, odors and excess minerals out of the water as it circulates. That keeps the water that keeps cycling through your terrarium cleaner, which slows down rot and mold, and stops a closed system from developing an unpleasant smell. A thin layer on top of your drainage layer is enough; more isn't necessary.
What's the purpose of moss in a terrarium?
Moss covers bare patches of soil, holds moisture at the surface, and helps stabilize the humidity inside your terrarium. It also stops soil from working its way down between the drainage material when you water, and it immediately gives your terrarium a finished, natural look. Curious which type of moss to use? Our moss guide covers cushion, silver, reindeer and dried moss and when to use each one.
What's the difference between cushion moss and sheet moss, and which is better?
Cushion moss (also called mood moss or ball moss) naturally grows in rounded, cushion-like mounds, giving it a thicker, sturdier structure. Sheet moss grows flat and spreads across the soil like a thin carpet. Neither is inherently "better": sheet moss is ideal for covering a surface tightly and evenly, while cushion moss adds more volume, variation in height, and a more natural, hilly landscape effect. In practice, many terrarium builders combine both for a varied result.
Do you need springtails in a plant terrarium?
Not strictly necessary, but springtails (collembola) are useful: they're tiny soil-dwelling creatures that clean up mold and dying organic matter, keeping your terrarium naturally cleaner and better balanced. A regular plant terrarium can do fine without them, especially if you check in on it yourself now and then, but in a bioactive or long-term closed system, they meaningfully reduce the chance of mold.
How does a ready-made DIY terrarium kit work?
A DIY kit includes every part you'd normally have to gather separately: drainage material, activated charcoal, terrarium soil, moss, hand-picked plants, and usually a step-by-step guide. You build up the layers yourself in your own glass container or the one included, exactly as you would with a fully self-assembled terrarium — the kit just saves you from sourcing individual parts or figuring out which plants pair well together.
Which plants
Which plants are suitable for a closed terrarium?
Choose small-leaved, moisture-loving plants that enjoy high humidity: fittonia, miniature ferns, peperomia, selaginella, maidenhair fern and compact pilea varieties are popular choices. What matters most is picking slow growers that stay small, so they don't outgrow their container within a few months.
Which plants are suitable for an open terrarium?
For an open terrarium, choose plants that tolerate drier air and don't depend on high humidity: succulents and small cacti are the classic choice. They lose little moisture through transpiration and handle the lower moisture retention of an open container better than tropical ferns or fittonia would.
Can I put cacti or succulents in a closed terrarium?
That's not recommended. Cacti and most succulents naturally come from dry environments and don't handle the high, constant humidity of a closed terrarium well — the risk of root rot is high. They belong in an open setup with fast-draining substrate, not behind a sealed lid or cork.
Which plants should I avoid in a terrarium?
Large, fast-growing houseplants aren't a good match: they quickly outgrow their container and throw off the system's balance. Flowering plants are also often discouraged, since fallen petals in a humid, closed environment rot quickly and can trigger mold. And as mentioned above, keep drought-loving plants like cacti out of a closed, humid terrarium.
How many plants can I put in my terrarium?
Less is more: give each plant enough room to grow rather than filling the container to the brim. Overcrowding competes for light and nutrients, blocks airflow, and increases the risk of mold. As a rule of thumb, leave some visible bare soil or space between plants when you set it up, even if it looks a bit sparse at first.
Care
How much water does a terrarium need?
Less than you'd think. For a closed 5-to-10-liter jar, about 50 to 150 ml of water is usually enough at setup — after that, the system can often go months thanks to its natural cycle. Overwatering is by far the most common mistake: only water again once the soil is visibly dry, not on a fixed schedule.
How often should I water my terrarium?
A closed terrarium often needs no extra water for months, as long as the cycle keeps going. An open terrarium loses moisture faster and needs watering more often, depending on the plant species and how dry the air in your home is. Always check the soil and glass rather than going by the calendar.
Where's the best place to put a terrarium?
Choose a spot with plenty of indirect light, about a meter from a window (closer is fine only for a north-facing window). Never place your terrarium in direct sunlight: the glass acts like a greenhouse, and the plants can literally burn. Turn the container a quarter turn weekly if you can, so the plants grow evenly instead of leaning toward the light.
Does a terrarium need (sun)light?
Yes, light is essential: without it, photosynthesis can't happen and the whole cycle inside your terrarium grinds to a halt. It just needs to be indirect light — bright, direct sunlight heats the glass too much and damages the plants. If your home is quite dark, a small grow light is a good alternative.
Is condensation on the glass normal?
Light condensation in the morning that clears up later in the day is a sign the water cycle is working well. If the glass stays fogged up all day and you can barely see the plants through it, there's too much moisture in the system: remove the cork or lid for a while until the excess moisture has evaporated.
Should I open my closed terrarium every now and then (airing it out)?
Yes, doing so occasionally is a good idea, especially during the first few weeks after setup. Airing it out helps against excess condensation and slows mold growth. A well-balanced terrarium can then stay closed for months at a time, but if you're ever unsure about the moisture balance, opening it briefly is never the wrong move.
Do I need to prune my terrarium?
Eventually, yes, though usually only once a year or so. Trim back oversized or overgrown leaves and stems as soon as they start crowding other plants, to keep the system in balance and ensure enough light and airflow remain.
How long does a plant terrarium last?
With the right spot, a good moisture balance, and the occasional bit of tending, a terrarium can last for years. It's not a static object: plants grow, some do better than others, and now and then you may need to replace or prune a plant. That's a normal part of the process, not a sign that something's going wrong.
Troubleshooting
Why is mold appearing in my terrarium, and what should I do about it?
Mold tends to show up in a warm, humid environment with too little ventilation or too much organic matter, and it's common in the first few weeks of a new terrarium. A small amount of white, fuzzy mold is usually harmless and part of the ecosystem settling in. Remove it with a clean, damp cloth or a piece of paper, then let the terrarium air out until the moisture level drops, and make sure it's getting enough light, since that naturally slows mold growth.
Why do I have tiny flies in my terrarium?
Small black flies around the soil are usually fungus gnats, which can already be present as eggs in potting soil and multiply in constantly damp soil. Let the top layer of soil dry out a bit (in an open terrarium) or air the whole thing out, so the environment becomes less attractive to the larvae. Fruit flies tend to show up when there's leftover fruit or sugary residue nearby, so keep that away from your terrarium.
Why are my terrarium plants dying?
The most common cause is a disrupted moisture balance: too much water keeps roots constantly wet and leads to root rot, while too little light weakens growth over time. Choosing the wrong plant for the type of terrarium (for example a cactus in a closed, humid jar) is another frequent culprit. If plants are struggling, check the soil moisture and light levels first before doing anything else.
Why is the soil in my terrarium dry, or too wet?
Dry soil in a closed terrarium usually means it's been opened too often, or it's simply time to add a small amount of water. Soggy, waterlogged soil points to overwatering or an insufficient drainage layer: leave the container open for a while so the excess moisture can evaporate, before sealing it again.
Ordering & shipping
Where does Urban Jungle ship my order from?
Every order ships from our own warehouse in Mierlo, the Netherlands. Orders typically go out within 1 business days.
Is shipping safe with all that glassware?
Yes. Every glass item is packed in a double box, with extra bubble wrap or recycled cardboard padding added wherever needed to keep it from moving in transit. In the rare case something does arrive damaged, we simply send a replacement straight away, free of charge.
What should I look out for when buying a terrarium (kit)?
Check whether the plants included are suited to the type of terrarium (open or closed) you want to build, and whether the basic layers — drainage, activated charcoal and terrarium soil — are included. A clear, step-by-step guide makes a big difference for beginners. Also check whether the container's opening is wide enough to fit plants and tools through, and whether the glass is sturdy enough for the weight and volume of the fill.