What Is a Terrarium? (And How Do They Work?)

Almost every time I talk to someone new about my green hobby, I get the same puzzled look and accompanying question. What is a terrarium?

Terrariums are miniature gardens, housed inside small – and usually sealable – containers like bottles and jars.

As fully functioning (albeit tiny) plant ecosystems, they’re mostly self-sustaining, with the plants watering themselves through transpiration and condensation. Science!

Great, so what does terrarium mean? That comes from the Latin terra (“earth”) +‎ arium (a place or receptacle). Like an aquarium, just plants and earth instead of fish and water.

Fancy definitions aside, terrariums are a beautiful, interesting and creative way to keep plants in the home. Whether you’re looking for a desktop companion, a contemporary way to liven up your home, or a fun project to do with the kids – terrariums are a great option.  

What is a Terrarium

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What is a Terrarium For?

Well, terrariums originally came about from a botany accident in Victorian London (how terribly exciting), where they quickly became a hot new trend as Victorians explored their love for exotic plants and ferns.

These days terrariums are used for much the same thing.

They’re perfect for people like me who love the natural world, but live in the city with no garden and little space for plants. Or for people who’d like a stunning collection of exotic plants that require very little maintenance.

As I say in our Essential Guide to Tropical Terrariums, terrarium building is the intersection between art and science (and that’s why I love it).

Fittonia Terrarium
Rae planting up our Fittonia Terrarium.

How do Terrariums Work?

Closed terrariums are fully functioning ecosystems, just miniaturised.

Understanding how they work is basically a lesson in the water cycle and the carbon cycle (yes, the same ones from school).

The warmth from the sun causes moisture to evaporate from the plants and soil, which then condenses on the cooler inside surfaces of the glass container.

Humid terrarium
One of my freshly watered tropical terrariums looking very steamy and humid.

Just like rainfall, the water then drips/falls back down into the soil and voila! The process starts again.

The soil provides nutrients for the plants, then – as is the natural order of things – those nutrients are replenished as the plants die and decompose into the soil.

Closed terrariums aren’t an exact science, and they can take a bit of trial and error to get right. Much like our own world’s ecosystems, they can be susceptible to changes in light, temperature and overzealous species.

But if you follow our guides, set up your terrarium properly, and pick the right terrarium plants – you’ll be set for success.

Types of Terrarium

These days, terrariums come in all shapes and sizes (literally, pretty much anything clear can be used as a container).

Generally, types of terrariums are dictated by what plants you try to grow in them. Tropical terrariums, succulent terrariums – you get the idea.

You could also argue that “open” and “closed” are types of terrarium.

Closed terrariums being the classical type (and the only type I’m really concerned with). Sealing off the terrarium and creating a closed system is what perpetuates the ecosystem… and lets us do all the fun things. After all, trapping humidity in terrariums is what first allowed the Victorians to grow their interesting tropical plants.

Open terrariums can lose many of the important features and functions of a true terrarium, but they still have their place.

They’re best suited to plants that don’t require much moisture.

Did I Miss Anything?

Is there anything you’re still not certain about after reading this article?

Let me know in the comments and I’ll do my best to answer.

2 thoughts on “What Is a Terrarium? (And How Do They Work?)”

  1. Thankyou! But can you tell me that,How can plants do photosynthesis in the terrarium if it is closed? Because plants need carbon dioxide to do photosynthesis that is in the atmosphere and if the jar is close so how the plants in the terrarium get Co2 for doing photosynthesis?

    1. That’s a great question! It’s mostly from bacteria in the soil that are breaking down any decaying organic matter and releasing Co2 (also, any breathing bugs if you have them).

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