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Why You Probably Shouldn’t Keep A Terrarium Outside

If you’ve just finished one of your first terrariums, I’m guessing you’re probably wondering, can you keep your terrarium outside? Your terrarium plants are found in the outdoors after all. Surely they must be fine sitting on your front porch, right?

The problem with keeping a terrarium outside is that the terrarium will be exposed to a large amount of direct sunlight. Too much direct sunlight can raise the internal temperature too high for the plants to survive. In general, it’s best to keep terrariums under indirect sunlight indoors to give them the best chance of survival.

While there are some exceptions to the rule, there are certainly better places to place your terrarium other than on your front porch or in your backyard. Besides placement, there’s also other things you could be doing to maximize the chances of your plants surviving.

Why terrariums should not be kept outside

One of the problems with keeping a terrarium outside is the constant exposure to direct sunlight. When a terrarium is exposed to direct sunlight, internal temperatures can rise very quickly and create a steamy sauna. Most plants can’t tolerate this kind of heat, so it’s best to keep them out of direct sunlight.

Terrariums act like little greenhouses. Light is absorbed by the plants/soil and released as heat by radiation, raising the temperature. Because everything is enclosed in a container, there’s nowhere for the heat to escape. Combined with the fact that there’s no wind carrying away excess heat via convection, the temperature is just going to keep rising.

Essentially what you have is a system that is constantly gaining heat, but has almost no way to release that heat.

So while you might see your plants out in the wild being exposed to direct sunlight, the situation changes once you place them in an enclosed glass or plastic container.

You can kind of think about it like the inside of a car on a hot day. Even though the outdoors might not be too hot, the inside of a car parked out in the sun is definitely going to be much hotter.

That’s why terrariums typically prefer to receive indirect sunlight. The intensity of the light coming into the terrarium is much lower, preventing the system from gaining too much heat.

There are exceptions if you contain plants that will flower like African violets or orchids. These types of plants love to stay in the heat and will be more tolerant of a warmer terrarium.

Where should I keep my terrarium?

The general rule of thumb about sunlight is that terrariums need roughly five to six hours of light exposure. So you should look to keep your terrarium in a spot that has access to sunlight, but is also shaded at the same time.

Once in a while, you will also want to turn your terrarium slightly to make sure your plants are growing evenly in all directions.

For the most part, anywhere indoors will do as long as you can see light coming in through a window. Just don’t place your terrarium right next to a window that receives the most sunlight.

In general, southern windows have the strongest light intensity while east-facing windows will receive morning sunlight that is not quite as strong.

However this also depends on your location. If you are on a hill, that’s obviously going to change which side of your house is receiving sunlight.

Another rule of thumb: higher floors will receive more sunlight because they have a better view of the sky from up there.

If you want to keep things simple, just place your terrarium anywhere in a room with a window, but not directly next to the window and you will probably be fine. You can always experiment with this to see what works best.

How do you keep plants alive in a terrarium?

To be honest, sunlight is probably the least of your worries when it comes to taking care of your terrarium.

But that’s not to say terrariums have a lot of problems to deal with. Most terrariums will actually require very minimal maintenance throughout their life spans.

Here’s my go-to checklist for things to watch for in a terrarium:

  • Proper water levels
  • Mold and fungus growth
  • Dying and decaying plant parts
  • A dirty container
  • Overgrown plants

The most common issue that people run into is maintaining the proper water levels. Too much water and you risk running into root rot and mold growth. Too little water and your plants will start to turn yellow and flaky.

Most beginners will probably lean towards over-watering their terrarium. It’s very easy to overestimate how much water a terrarium will actually need, especially when comparing how much water a common house plant will need.

Since terrariums are closed up in a container, there’s very little water actually evaporating from the system. The water that does evaporate recondenses on the walls of the container and trickles back down into the soil.

Because of this, terrariums will actually need very little water to survive.

The two ways to check the water levels are to:

  1. Observe the condensation on the container
  2. Feel the soil in the terrarium

If you’re seeing condensation on the walls of the container all day, that’s a sign there’s too much water. There should mainly be condensation on the glass in the mornings and evenings, but any more than that may mean too much water.

Similarly, if you see no condensation on the container, there’s probably too little water.

The second way you can verify this is to feel the soil in the terrarium. If it feels dry, there’s too little water. If it feels soggy, there’s probably too much water.

If you find yourself with too much water in your terrarium, you can let it air out for a couple of hours to let some of the water evaporate from the system. You can also wipe off some of the condensation with a paper towel to remove some more water on top of that.

Re-watering should be pretty simple. Just give a quick mist or a few spoonfuls of water and you should be good to go.

I didn’t really go over the rest of the things you will have to check for, but if you want to learn more about maintenance, you can check out my other post here.

The other thing you will want to do from the very beginning is make sure that you are setting up the structure of your terrarium correctly with the right plants. If a terrarium is not set up correctly, that may lead you to run into problems down the road which can shorten the lifespan of your terrarium.

How long can a terrarium last?

While everyone hopes that their terrarium will last a long time, that’s not always the case.

If they’re not properly cared for or the plants selected for the terrarium are not suitable, they might not last even for a few weeks.

At the same time, the longest recorded living terrarium has been alive since 1960.

The story is also a little bit more complicated because a terrarium is a complete ecosystem rather than an individual plant species. Because of this, you might see some plants die, but others continue to thrive, much like an ordinary ecosystem.

It’s also a little bit difficult to gauge because you can always replace the plants that have died with new plants to take their place. So in that sense, you’re keeping the overall terrarium alive by replacing the dead components like a frankenstein monster.

For the most part, terrariums will generally stay alive until they run into a problem that causes your plants to start dying out. This includes things like rot, mold, and overheating.

So with proper maintenance, you’re helping your terrarium to last longer than it would otherwise on its own.

As a rule of thumb, you will want to aim for a lifespan of about 3 to 5 years with proper maintenance. In my opinion, that’s a pretty reasonable lifespan for something you built from scratch.