Picking the Right Jar or Vessel for Your Terrarium
Before soil, plants, or moss ever enter the picture, a terrarium starts with a container, and that choice quietly shapes almost every decision that follows — how easy planting and maintenance will be, how much humidity the setup can hold onto, and which plants will actually have room to grow into their mature size.
Cylinder jars
The classic straight-sided jar is the most forgiving shape to plant and maintain, simply because its consistent width from top to bottom means tools, hands, and watering cans can reach every part of the interior without much fuss. It suits almost any plant list and any layer depth, which makes it a sensible first vessel if you're still finding your footing with terrarium building generally.
Glass globes and spheres
A rounded glass globe makes a striking display piece, but the curved shape narrows dramatically toward the base, which limits how deep a substrate stack you can comfortably build and how much you can physically reach once it's planted. Globes tend to suit smaller, simpler plantings — a single air plant, a small cushion of moss, or a couple of very compact specimens — rather than a dense, multi-layered garden.
Bell jars and cloches
A domed glass cover paired with a flat base or shallow dish gives you the presentation of a sealed terrarium with much easier access than a narrow-necked jar, since the whole dome typically lifts away for planting and maintenance. This shape works well for a closed, humidity-loving planting of moss and small ferns, and the wide base gives you more floor area to arrange plants across than a tall, narrow jar of similar volume would.
Rectangular tanks
An open-topped rectangular tank — often repurposed from small aquarium stock — gives you the most floor area relative to its footprint and the easiest access of any shape on this list, since there's no narrow opening to work around at all. It suits larger, more elaborate plantings with multiple species, varied heights, and hardscape elements like rocks or driftwood, and it's the natural choice for an open terrarium built around air plants or small succulents.
Matching the vessel to your plan
A few practical questions narrow the choice quickly. If you want to build a dense, layered planting with several plant types, favour a wider vessel with real floor area — a tank or a bell jar over a narrow jar or globe. If your hands or tools need to reach every corner regularly, a straight-sided jar or an open tank will frustrate you far less than a curved globe with a narrow neck. And if display and shelf space are the priority over planting complexity, a globe or a smaller cylinder jar takes up less room while still making a strong visual statement.
It's also worth thinking ahead to maintenance access specifically: trimming an overgrown fern, replacing a patch of moss, or fishing out a fallen leaf is a five-second job in an open tank and can be a genuinely fiddly one through a narrow bottle neck. If you already know you'll want to rearrange things occasionally, weight that against how much you value the sealed, minimal-maintenance quality of a true bottle terrarium.
Lids and ventilation
The lid, where there is one, is as much a design decision as the body of the vessel. A tight cork or ground-glass stopper seals in humidity most completely and suits a true closed terrarium built around moss and ferns. A loosely resting lid, or a bell jar propped open a crack, gives a middle ground — more humid than fully open, but with enough air exchange that mould and over-fogging are less of a risk. Some cylinder jars and tanks are sold with mesh or vented lids specifically so you can keep air-plant or succulent displays open to airflow while still cutting down on dust settling over the top.
Once you've settled on a shape, working out its actual volume — and how much of that you'll realistically use once the layers and plants are in — helps with buying the right amount of substrate and drainage material rather than guessing. The jar & vessel volume calculator on this site covers cylinder, sphere, bell jar, and rectangular shapes and gives both the total and a realistic usable-substrate estimate.