Choosing Plants for an Open or Closed Terrarium (Including Which Are Pet-Safe)

Vessel type should decide the plant list, not the other way around. A closed terrarium and an open one create such different conditions — humidity, watering frequency, how much moisture sits around a plant's base — that trying to fit a plant suited to one style into the other is one of the most reliable ways to lose it within the first month, and it's a far more common cause of an early failed terrarium than any single mistake in watering technique. This is a practical shopping guide to what actually suits each style, plus a plain rundown of which popular options are worth knowing are toxic if a pet or small child chews on them, since a terrarium usually sits at exactly the height — a shelf, a desk, a coffee table — that makes it reachable, in a way a plant on a high windowsill or a hanging basket typically isn't.

Closed terrarium plants

Moss and true ferns are the reliable core of a closed-terrarium plant list, covered in more depth elsewhere on this site — they want the stable, high humidity (roughly 80–95% for this pairing) that a sealed vessel provides and struggle without it. A few other genuinely good closed-terrarium options worth knowing: nerve plant (Fittonia), grown for its strikingly veined leaves, wants consistently high humidity and handles a sealed jar well; baby's tears (Soleirolia soleirolii) forms a dense, mossy-looking mat of tiny leaves and spreads readily in humid conditions; and pilea species generally tolerate the same stable dampness comfortably. All three of these, like true ferns and moss, are generally considered non-toxic to cats and dogs, which makes them a reassuring core list for a closed jar in a home with pets.

Two popular trailing plants come up constantly as closed-terrarium additions in photos and plant-shop displays, and are worth flagging specifically: pothos (Epipremnum aureum) and philodendron. Both tolerate high humidity well and look striking trailing over a jar's rim, which is exactly why they're so often suggested — but both are toxic to cats and dogs if chewed, and can cause mouth and throat irritation in people too. That doesn't rule them out, but it's worth knowing before adding one to a jar that pets or small children can reach, especially since trailing stems draped over a jar's rim are exactly the part most likely to catch a curious cat's attention.

Open terrarium plants

Air plants (Tillandsia), covered in depth elsewhere on this site, are the classic open-terrarium choice and are generally non-toxic to cats and dogs — genuinely good news given how often they're displayed at coffee-table height. Among succulents, haworthia and echeveria are both popular, compact, non-toxic options that suit an open vessel's lower humidity well, making them a safe default pairing for a display near pets or kids.

Several other open-terrarium succulents are worth knowing are toxic, though, since they're just as commonly sold and displayed: jade plant (Crassula ovata), string of pearls (Senecio rowleyanus), and aloe vera are all toxic to cats and dogs if chewed. Kalanchoe is toxic too, and worth taking seriously — it's one of the more commonly reported culprits in pet-poisoning cases among houseplants generally, not just among succulents, and it's sold widely as a flowering houseplant well beyond terrarium and succulent contexts. None of this means these plants can't be grown at all; it means placement and household context matter as much as the plant's care needs do.

The toxicity list at a glance

Generally non-toxic to cats and dogs, and reasonable defaults for a home with pets or small children: true ferns (Boston, maidenhair, bird's nest, table), true mosses and spike moss, air plants (Tillandsia), nerve plant, baby's tears, pilea, haworthia, and echeveria.

Toxic to cats and/or dogs if chewed, and worth extra caution around reach and placement: pothos, philodendron, English ivy, jade plant, string of pearls, aloe vera, and kalanchoe. Several of these are also documented as causing mouth or skin irritation in people, including children, if chewed or handled roughly.

This isn't a complete list of every terrarium or houseplant option, and it isn't medical or veterinary advice — it's a starting point for checking a specific plant before it comes home, and it's worth double-checking directly for any plant not covered here. If a pet or child does chew on a plant and you're not sure whether it's a concern, a vet or poison control line is the right call, not a guess based on a general list like this one.

It's also worth flagging that toxicity and general safety aren't quite the same question. A plant can be non-toxic and still cause a scratch or minor skin irritation from a sharp edge or rough texture — some succulents have genuinely sharp leaf tips, for instance, independent of anything chemical. And a plant being toxic doesn't automatically mean severe illness; the severity ranges widely across the toxic list above, from mild mouth irritation to more serious effects, which is exactly why "toxic" is worth treating as a flag to check further rather than either a reason to panic or a detail to shrug off.

Checking before you buy, not after

The most reliable way to use a list like this one is to check a specific plant's name against a trusted source before it comes home, rather than trying to remember a list from an article days or weeks later at the shop. Plant tags at nurseries and garden centers don't reliably flag toxicity, and the same common name sometimes covers more than one species with different safety profiles, so a quick search for the plant's scientific name plus "toxic cats dogs" before buying is a more dependable habit than relying on memory. This matters more for a terrarium than for most houseplants specifically because of where terrariums tend to live — a shelf, a desk, a coffee table — all well within reach of a curious pet or a toddler exploring at that exact height, unlike a hanging planter or a high shelf that's naturally out of range.

It's also worth remembering that "non-toxic" doesn't mean "fine to encourage." A cat chewing on a fern frond or a dog mouthing an air plant isn't likely to be poisoned by it, but a mouthful of substrate, drainage gravel, or fertiliser residue is a different matter, and physical irritation from stiff or fibrous plant material can happen even without any chemical toxicity involved. Keeping a terrarium as something to look at rather than something a pet is encouraged to interact with directly is good practice regardless of which plants are inside it.

A worked example: fitting a plant list to a real container

Take a 30 x 20cm rectangular tank — 600cm² of floor area, a common size for an open terrarium built around a few succulents or air plants. Planted at a "moderate" density, that floor fits about twelve plants at a compact 6cm mature spread (several small echeveria or haworthia rosettes, say), but only about four at a 10cm spread, and around two at a larger 15cm spread. A "sparse" density, useful if you want visible room for growth over the following months, drops those same numbers to roughly seven, two, and one respectively; a denser "full" planting pushes them up to about eighteen, six, and two.

The gap between those numbers is worth sitting with before you shop: doubling a plant's mature spread from 6cm to roughly 10–12cm doesn't just modestly reduce how many fit — it cuts the count by more than half, because the calculator is working with each plant's canopy area, which grows with the square of its spread, not its spread directly. A plant twice as wide at maturity takes up roughly four times the floor space, not twice, which is easy to underestimate when you're picturing a small starter specimen rather than its grown-out size. Buying six small echeveria rosettes for a floor that only comfortably fits two full-grown ones is a common and avoidable overcrowding mistake, and running your own container and plant list through the plant count calculator on this site before buying catches it early.

Humidity targets once the plant list is set

Once you've matched plants to vessel type, the humidity guide calculator on this site turns that pairing into a concrete target and misting cadence. In a room sitting at a fairly typical 40% ambient humidity, an open terrarium of air plants targets roughly 40–60% relative humidity, with misting a bit more than twice a week to hold it. A closed terrarium of moss and ferns in the same room targets a much higher 80–95%, with misting settling to around three times a week — a useful reminder of just how differently the two styles need to be run, even before any single plant's individual preferences come into it.

When you genuinely want to mix styles

Occasionally a display calls for both a closed-terrarium plant and an open one side by side — a divided vivarium-style build, or simply two separate small vessels displayed together rather than one shared container. That's a reasonable way to get both looks without compromising either plant's actual needs, and it's a better solution than trying to find a humidity compromise that satisfies neither a moisture-loving fern nor a drought-tolerant succulent particularly well — a genuine middle-humidity setting tends to leave both plants merely tolerating their conditions rather than thriving in them. If you do want a genuinely mixed single container, treating it as an open, well-drained build with only the more humidity-tolerant end of the closed-terrarium list (bird's nest fern, for instance, which handles a range of humidity reasonably well) gives the best odds of both sides surviving together.