What Kind of Terrarium Should You Use for Growing Moss and Tropical Plants? Let’s Talk Humidity and Ventilation

Mosses and tropical plants thrive in humidity. The most effective way to maintain that humidity? A closed glass terrarium.

Now, a lot of people think: “A good closed terrarium must be airtight. The fewer the gaps, the better it works.”I get where this idea comes from. You’ve probably heard that old viral story about a British guy who sealed a plant inside a giant glass bottle, left it in a stairwell, and opened it 20 years later to find a tiny jungle inside. Pretty cool—but let’s be honest: the plants weren’t exactly thriving in the aesthetic department. If you’re going for that “forgotten science experiment” vibe, then sure, seal it up tight.

But if your goal is to grow lush, healthy moss or to raise tropical plants with ideal form and size, then both humidity and ventilation matter. It’s not the terrarium alone doing the work—you manage the conditions.

Take NCYP’s closed terrariums, for example. They all have doors—and small gaps around those doors. They function like mini indoor greenhouses, perfect for moss, ferns, and small tropical plants. Most are under 16 inches tall, great for beginners or simple setups. You control humidity and ventilation manually—open the door and mist inside occasionally.

These terrariums are designed for indoor use. They won’t raise temperatures much, but they’re fantastic at locking in moisture. (check the following photo. It is a typical with door close terrarium).

1. Is a More Airtight Terrarium Better for Moss?

Short answer: No.

Here’s why: in the wild, no moss grows in a completely sealed environment. Take Leucobryum moss, for example. The healthiest patch I’ve ever seen was under a thick canopy of bamboo, layered with shrubs and weeds. Hidden beneath those layers? A gorgeous, thriving moss bed.

That’s not a sealed space—it’s shaded, damp, and ventilated. Mosses love stable humidity, but not stale, stagnant air. Still air makes moss leggy and can even lead to disease.

Need proof? Check these examples:

• Leucobryum growing in a closed NCYP terrarium (door rarely opened).

  

And this one. This one is never trimmed and closed most of time,shows clearly how "tall" they are.

• Hypnum moss going wild inside another closed terrarium. Compared to its wild version, the shape and texture are totally different.

  please check this video:

That’s why we don’t try to eliminate door gaps—and in some models, we even add vent holes! The goal isn’t to vacuum-seal your plants, but to replicate a forest floor’s microclimate: humid, shaded, and breathing.

People often ask about the small gaps around the doors. Here’s the deal:

1. These terrariums are hand-soldered, and slight gaps at the joints are part of the craftsmanship.

2. Even with gaps, they hold humidity well. You’ll see Leucobryum thriving inside, and sometimes mushrooms pop up on their own. The gaps actually help—they allow gentle airflow.

Why Does Ventilation Matter?

Ventilation helps in two big ways:

• It lets excess heat escape, especially in warmer months.

• It makes life harder for mold and mildew.

I always recommend using a spray bottle—not just to keep things moist, but because opening the door to mist also brings in fresh air.

Airflow also affects how your moss grows. Less ventilation = tall, stringy moss. More ventilation = denser, tighter growth. This is because airflow reduces the "boundary layer" that moss has to grow through.

Photo comparison:

• Hypnum moss in a sealed terrarium—tall, thin, slightly floppy.

  (the following two are taken when just planted)

  

  

in 1-2 months:

• Hypnum moss in a terrarium with vents—shorter, more compact, and lush.

  in 1-2 months since planted.

  

  

  

  

Pro tip: I don’t recommend closed terrariums for Hypnum moss.For Leucobryum, it depends on your goal: want it tall and layered? Reduce airflow. Want a tidy carpet? Add airflow by opening the door more often.

2. Do All Mosses Need Closed Terrariums?

Nope. Different mosses = different needs.

To grow healthy, photogenic moss, you need both humidity and airflow in the right balance.

From my personal moss collection:

• Leucobryum moss prefers still, humid air. Closed-door terrariums work great.

  

  

  

  

  

• Hypnum moss likes more airflow. I use open-top aquarium-style terrariums—no lid, no drainage needed. These retain some humidity near the bottom but breathe freely at the top.

Here is what the hypnum moss looks like:

Vented closed terrariums can also work well for controlling wild growth—see the photos for comparison (for the moss status, please check above).

If you’ve got a DIY waterfall or stream feature, try placing Hypnum or Plagiomnium moss on the rocks. They’ll cling like green tattoos.

The moss that loves airflow most? Bryum argenteum—also known as “that moss growing on your garden steps.” It's super common in human-inhabited areas. You don’t even need to buy it—it’s probably already in your backyard. But it hates still air. It needs high ventilation and bright indirect light—not ideal for indoor terrariums.

3. Where Do You Get the Perfect Plants for These Terrariums?

Besides moss, I grow tropical mini plants like ferns and begonias. Some I collect from the wild, some I buy, and some I propagate at home.

Bad news: It’s tough to find perfectly sized plants for terrariums in stores.

Good news: They’re super easy to grow from cuttings inside terrariums!

In fact, closed terrariums are ideal propagation stations. Place a begonia leaf inside, and boom—it sprouts roots. Soon you’ll have a bunch of adorable baby begonias. This works for many tropical plants—even bonsai cuttings!

there are more videos in my youtube and these are two of them.

Want to slow their growth? Reduce humidity and use minimal, shallow soil.Humidity = fast growth. Reduce it later to stabilize size—especially helpful for keeping begonias compact.

Here is a terrarium projects I want to share. First it is the building video. pay attention to the begonia size: it is a typical small begonia with a large leave.

a clip taken over 1 years later. pay attention to the begonia leaves. it is much smaller and tight, right?

4. Won’t Shallow Soil Hurt the Plants?

Not at all. Tropical plants in terrariums aren’t picky. Many can grow on bark, rocks, or even moss. Shallow soil is fine—they care more about humidity than root depth.

In all my terrariums, the planting subtrate are shallow. They are all will be below 5cm thick.

check the previous video above. the soil on the glass is just only about 1cm thick.

See the below photo. even with a begonia, its planting layers are so thin. And the plants grows well. I will add a follow-up video / photos here later.

5. What Kind of Soil Should I Use?

Whatever you have on hand! I often use clay, volcanic rock, or diatomite—mainly because they look clean and tidy.

6. Why Do Your Plants Look Different From Online Photos?

Because mine are homegrown—and plants adapt to their environments. Moss grown indoors tends to be lighter green (which I actually love). And some plants, like Saxifraga stolonifera, develop richer colors in high humidity and low light.

7. How Do I Find the Right Balance of Humidity and Airflow?

Trial and error.

We’ve already covered some popular moss above. For tropical plants like begonias, grow them fast in high humidity, then reduce humidity to maintain size and shape. It’s all about observing and adjusting (there will be a comparing video later). Thin planting soils works too.

8. Can I Keep Bugs Inside? What About More Vents or Doors?

Absolutely.

Some of our terrariums have built-in vents.Our tin models with clear or black mesh vents trap humidity well but still allow minimal airflow—perfect for damp-loving insects like isopods or springtails. Mushrooms and mold might appear—just wipe or spray them off.

Terrariums with larger mesh vents have excellent airflow but retain less moisture. Great for ferns like maidenhair—but beware, even they might yellow in dry air.Bonus: no foggy glass, no mold.

Let me know if you want photos, videos, or more details—I’ll keep updating this post!Got questions? Leave a comment. Want to see a specific setup? Just ask.