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. Four shapes cover the large majority of terrariums people actually build, and each one trades off differently between display appeal, floor area, and how easy the interior is to reach.

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. A modest 18cm-wide, 25cm-tall jar holds a little over 6 litres total, with roughly 3.8L of that realistically usable once you leave headspace for airflow and growth — enough for a genuinely layered small build without being unwieldy to work in.

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. A 15cm globe holds under 2 litres total (about 1.8L, roughly 1L of that usable), which is a helpful number to keep in mind before assuming a striking display piece will also hold a lot of plant.

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. Because the dome itself is largely headspace rather than usable layering room, it's worth measuring the straight-sided base separately from the total height when you're working out how deep to build the substrate stack — the dome's curve narrows too quickly to hold soil the way the base does.

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. A 30 x 20 x 20cm tank holds a full 12 litres, with about 7.2L usable — roughly double a mid-sized cylinder jar's usable volume for a similar footprint on a shelf, since a rectangular shape doesn't lose volume to a curved wall the way a globe or bell jar does.

Comparing shapes at a glance

Putting real numbers side by side makes the trade-offs concrete. That 18cm cylinder jar, the 15cm globe, and a 20cm bell jar with an 18cm straight-sided base all sit in a broadly similar size class, yet their usable volumes and floor areas differ meaningfully: the cylinder and bell jar both give you real, flat floor area to arrange plants across, while the globe's curved base eats into both floor space and comfortable digging depth even at a similar overall size. Stepping up to a 30cm cylinder or a small rectangular tank roughly doubles the usable volume again, which matters most if your plant list runs to more than two or three specimens plus a moss carpet, or if you're planning hardscape elements like rock or driftwood that eat into the floor area without adding any growing room. The vessel size reference on this site lays out these figures — volume, floor area, and the layer depths each size calls for — across eight common sizes in one table, which is a faster way to compare options than running the calculator repeatedly by hand.

Glass, weight, and where it will actually live

Glass is by far the most common material for a reason: it's inert, doesn't scratch or cloud the way some plastics and acrylics do over time, and its clarity is part of the point of a terrarium in the first place. It is also heavy, and that weight adds up fast once substrate, drainage material, and moisture are factored in — a filled 30cm tank is a genuinely two-handed lift, not something to plan on repositioning casually once it's built. If a terrarium is going somewhere you'll want to move occasionally, like between a windowsill in winter and a shadier spot in summer, that's worth weighing against the appeal of the largest vessel you can find.

A curved globe or a bell jar's domed top does something a flat-sided tank doesn't: it can act somewhat like a lens, concentrating direct sunlight onto whatever's directly behind the curve. Combined with the general rule that direct sun heats glass and whatever's inside it faster than the same light would affect an open pot, this makes curved vessels worth keeping a little further from a sunny window than a flat-sided tank of the same general size, even though the ambient light level might look similar to the eye.

Placement also interacts with the open-versus-closed decision covered elsewhere on this site: a shape that seals well (a jar with a tight lid, a bell jar with a snug base) makes the most sense if you're planning a closed, humidity-loving build, while an easily-vented shape suits an open build of air plants or succulents better regardless of which of the four shapes you land on.

Glass versus acrylic

Acrylic and other clear plastics show up occasionally as a lighter, shatter-resistant alternative to glass, particularly in larger tank-style vessels where weight is a genuine practical concern. The trade-off is durability of a different kind: acrylic scratches far more easily during routine cleaning and rearranging, and unlike glass it can cloud or yellow slightly with age and UV exposure, which glass essentially never does under normal indoor conditions. For a smaller display handled carefully and kept out of direct sun, that difference may never become noticeable; for a larger, more frequently rearranged build, or one that lives somewhere it gets real daylight, glass tends to hold its clarity better over the years a terrarium is meant to last.

Cleaning and caring for the vessel itself over time

The container needs its own occasional maintenance separate from anything happening to the plants inside it. Hard water and misting residue build up gradually on interior glass, particularly right at the waterline in an open dish or the lower walls of a closed jar, and a soft brush or cloth on a long handle reaches most of this without disturbing the planting the way trying to scrub with a hand jammed through a narrow neck would. The exterior is simpler: a standard glass cleaner works fine, applied to a cloth rather than sprayed directly, so nothing drifts in through a lid or open top onto the plants themselves. A build that's otherwise perfectly healthy can still look tired and dull once residue accumulates on the glass, so this bit of housekeeping is worth folding into a terrarium's longer-term care alongside pruning and thinning.

Matching the vessel to your plan

A few practical questions narrow the choice quickly, and it's worth working through them before you fall for a shape purely on looks. 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 — long-handled tools help, but they're no substitute for a shape that simply doesn't fight you. 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, even with a shorter plant list than a larger vessel would support.

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, weigh 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.

The vessel and the lid together also decide, indirectly, which plants are safe to include if pets or small children share the home. A fully open tank at coffee-table height puts anything inside it within easy reach, which is worth weighing alongside a plant's toxicity, not just its care needs, when a display isn't going somewhere out of reach.

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, and running a few candidate sizes through it before you buy is a cheap way to avoid coming home with a container that's either cramped for your plant list or several times larger than it needs to be.