Picking out a container for your terrarium is one of the most exciting parts! It can be almost anything transparent, so the options are limitless.

I realized recently that most of my desire to create terrariums comes from the actual terrarium itself rather than the contents. I’ll see a big jar or a cool glass container and immediately think “Wow, that would make a sick terrarium.”

They don’t have to be particularly fancy or large to be successful or interesting-looking terrariums. So, what are the qualities to consider in a terrarium container?

Should a terrarium container be sealed?

We’ve already discussed in the post Sealed vs Unsealed Terrariums the question of whether or not your terrarium should be airtight, as well as the pros and cons of each method.

You should know which style you’d prefer before you get to the stage of picking out a container. Sure, it’s easy to flip a jar between being sealed and unsealed – you just have to unscrew the lid. Other potential terrarium vessels, like a fish bowl or another piece of glassware, could be difficult to seal.

The decision about whether or not your container should be sealed is independent of choosing a container, if that makes sense. If you want a sealed-type of terrarium then pick a sealed container. If you don’t want to do it that way, that’s fine too. The other qualities of the container are more important anyway, so that’s what we’re going to discuss.

Terrarium Container Material

There are two primary considerations here:

  1. Is the material non-reactive?
  2. Is the material transparent?

It almost seems silly to break down what is really a very simple concept. 99% of terrariums are made of glass or plastic, and that’s because they perfectly suit both of these factors.

You could make a terrarium in a cardboard box if you really wanted, I guess. You wouldn’t be able to see it except when you opened it since cardboard isn’t very see-through. Also, it’s a reactive material so it would start to rot pretty quickly.

A slightly better option is clay or ceramic. That’s non-reactive, but it’s not exactly easy to see through either. I suppose you could just look in from the top, but that just makes it a potted plant, doesn’t it?

Yeah, you’ll wanna stick with glass or plastic for your terrariums.

Be sure to choose a colorless material. Not only does it ruin the view, but colored material filters out the light that makes it into the container. Blue glass, for example, would prevent any blue light from penetrating. That’s not ideal because plants use light from the whole visible spectrum to photosynthesize (although they primarily utilize red and blue wavelengths).

Plastic Terrariums

Plastic comes with a few caveats. It hardly needs to be said that plastic can be subtly dangerous, either through leaching chemicals or shedding microplastics. You don’t want any of that stuff in your miniature ecosystem (or the real-world ecosystem for that matter).

To be totally honest, it’s very unlikely to have any noticeable effects on a terrarium. Most of the harmful effects take place over the course of decades and usually in adverse conditions (such as exposure to intense sun or wave action). And, generally, plants are more forgiving of such conditions than animals.

If you want to play it safe, though, stick to HDPE and LDPE plastics. That’s high and low density polyethylene. You can identify it by the little recycle triangles with the numbers in them – HDPE is 2 and LDPE is 4.

plastic types

While they are the safest types of plastic, our friends 2 and 4 don’t always come in totally transparent varieties. They do sometimes, of course, so keep an eye out.

Glass Terrariums

The undisputed champion material of terrariums, and for good reason. There are practically no downsides. It’s fragile, true, but maybe you shouldn’t be dropping small ecosystems in the first place?

The only to remember is to wash out the glass thoroughly before using it. There may be chemical residue from glass cleaner which absolutely could ruin the whole terrarium.

When picking out a glass terrarium, give preference to containers with thinner glass. It allows more light through but it also allows more heat out, reducing the greenhouse effect a little bit. It’s very possible to cook your terrarium, so it’s worth the effort to avoid it.

Terrarium Container Size and Shape

Terrariums can be made in any size and shape. Anything from a tiny one-inch vial of moss to a whole greenhouse (or even Biosphere) could qualify as a terrarium. To be honest, there aren’t a lot of rules that define what a terrarium is.

Let’s be a little realistic, though. Most people’s terrariums will range in size from a peanut butter jar to a 30 gallon fish tank. As a general rule of thumb, bigger terrariums will be healthier than small ones. There are several factors that go into that generalization, but the nitty-gritty is a topic for another post.

The short version is that more space, more volume specifically, is a buffer for changes in the soil and air chemistry. Any problems will propagate more slowly so they’re easier to address in time. It’s easier to balance the system when there’s more room to work with, both literally and figuratively.

This stays true as the size scales up. It’s very easy to regulate an ecosystem that’s the size of, say, the Earth. (Not that we’re doing a great job of it right now.) Taking care of a whole garden is easier than taking care of a jar-sized sample of the same. Not in time spent on labor, of course, but in that the garden is more resistant to mistakes you might make and more resilient and able to bounce back.

The shape is pretty unimportant, however, as long as it doesn’t interfere with the light getting in. Ideally it would be tall enough to accommodate the full growth of the plants you’ll fill it with. You can choose small plants to fit in a small terrarium, or commit to pruning regularly.

I can imagine some very limited scenarios in which the shape of a container would be an issue. If it were a sealed terrarium, there’s a small scale water cycle occurring. If the shape prevented the water from precipitating back into the soil, that would be a problem.

That’s an extremely-unlikely situation, so we’re gonna say that shape doesn’t really matter. Bigger is better. Use glass or plastic without coloring. Pretty easy right? It’s not limiting at all – you can make an excellent terrarium out of a huge range of materials.