Open vs Closed Terrariums: Which One Should You Build?

The single biggest decision in planning a terrarium isn't the jar or the plants — it's whether the container will be open or closed. That one choice shapes almost everything downstream: how humid the inside gets, how often you'll water, and which plants will actually thrive there. Neither style is objectively better; they're suited to different plants and different amounts of attention.

What "open" and "closed" actually mean

An open terrarium has no lid, or has one that doesn't seal — a wide-mouth bowl, an uncovered glass tank, or a jar with a loose-fitting top. Air moves freely in and out, so moisture that evaporates from the substrate and plants escapes into the room instead of staying trapped. A closed terrarium has a tight-fitting or sealed lid, so the moisture cycle happens almost entirely inside the glass: water evaporates from the substrate, condenses on the cooler glass walls, and drips back down, over and over.

Humidity and watering

This is where the two styles diverge most. A well-established closed terrarium can often go weeks, sometimes over a month, between waterings, because so little moisture actually leaves the container. The trade-off is that you need to watch for the opposite problem — a persistently fogged-up interior or mould developing on the substrate means too much moisture is trapped, and the lid needs to come off for a while to let some out.

An open terrarium behaves much more like a regular houseplant: it dries out at a pace closer to normal room conditions, so it needs more frequent attention, especially in a heated room in winter when indoor air runs dry. In exchange, it's far more forgiving of a slightly overzealous watering, since there's nowhere for excess humidity to get trapped.

Which plants suit which style

Closed terrariums are the natural home for plants that come from consistently damp, humid places — mosses, many ferns, and other shade-loving plants that would struggle in a dry room. They rely on that stable, high humidity to look their best. Open terrariums suit plants that prefer to dry out between waterings and don't want constant dampness around their leaves — succulents, cacti, and epiphytic air plants generally do far better without a lid trapping moisture against them.

Mixing the two groups in one container rarely ends well: a succulent in a closed, humid jar tends to rot, while a moss carpet in a dry, open dish tends to crisp up and brown. Picking the vessel type before the plant list, rather than after, saves a lot of frustration.

Maintenance day to day

A closed terrarium, once established, is genuinely low-maintenance — the main task is watching the condensation pattern and cracking the lid open occasionally to vent excess moisture or let in fresh air. An open terrarium needs more regular watering and, because it isn't sealed, dust and debris can settle on the surface over time, so an occasional light clean-up keeps it looking its best.

Both styles benefit from a spot with bright, indirect light rather than direct sun, which can heat the glass and cook whatever's inside far faster than the same light would affect a plant in open air.

Making the call

If you want something that mostly takes care of itself and you're drawn to moss, ferns, and other lush greenery, a closed terrarium is worth the slightly fussier setup. If you'd rather keep an eye on things regularly, enjoy air plants or small succulents, or want easy access to groom and rearrange the display, an open vessel is the more practical choice. Either way, the humidity guide calculator on this site will give you a target range and a suggested misting cadence once you've settled on a style and a plant category.