Hermit Garden

Here’s how long terrariums last: Results from my experiment

Everyone who’s built a terrarium or grows indoor houseplants wants their little plant children to do well and last for a long time. Probably the most common metric people want to use to evaluate how they’re doing is how long their plants last compared to how long they’re supposed to last. The real question is, how long are terrariums supposed to last?

A terrarium will last indefinitely with no fixed lifespan if well-cared for. Except for annuals and biennials, plants do not have a fixed lifespan. Their mortality is determined by external factors rather than a genetically programmed aging process like that of animals.

You might be surprised to hear that most plants do not age as animals or people do. That’s because their genetics and biological anatomy are much different than that of animals.

How long terrariums last: results from my moss experiment

I’m guessing you probably didn’t come here to hear me say that terrariums are supposed to last forever. That may be true in theory, but I can give you a better estimate of what you can practically expect with your terrarium from my own experience.

You should expect your terrarium to last anywhere from 4 months to a couple of years. 

To find out how long you might expect plants to last, I decided to run a simple experiment.

I harvested a piece of moss from my local area and placed it in a small ziplock bag. I gave it a little bit of water and sealed it off for good. I placed it on my dining room table where there’s a decent amount of indirect light.

In the beginning, the moss seemed to be doing fine. It was still looking green and was showing signs of condensation in the bag. That lasted for a few months or so.

Around month 4 or so, the piece of moss started to turn slightly brown. By month five, it was very obvious that my moss was completely brown. At this point, it would be fair for someone to question if my moss was still alive or not.

I tried taking a piece of moss out and placing it into another terrarium after giving it some water to see if it would turn green again.

About a month after that, I didn’t see any change in color. It was still looking a dark shade of brown. 

That pretty much confirmed it: my moss was dead.

So let’s do a little debrief of that experiment. Essentially what I did was I took perfectly healthy moss and placed it in a condition with zero nutrients. Just water and some air.

After 5 months, the piece of moss died. 

What we can conclude from that is that the good health of your plants will carry your plant along for a few months or so until any poor conditions will kill it off.

This essentially sets a lower bound on a lifespan that you can expect for your terrarium: about 4 months. Although, I can see it being shorter if you are placing your terrarium next to a heater or directly under intense sunlight.

As for the upper limit, I think with decent care, you should expect your terrarium to last about a few years in optimal conditions with zero maintenance. 

Eventually, your soil is going to run out of nutrients as it’s consumed by your plants. Your plants might also outgrow the container and will have to be re-potted.

However, your terrarium can always be maintained such that any dead plants are removed and its soil replaced if needed. You can kind of think about that as a reset on your terrarium’s timer.

How plant aging works

Let’s get back to plant aging theory for a bit here.

Plant aging is also called senescence and it’s an active area of research for plant biologists.

There’s way too much content to cover in just one blog article, so I’ll just give you a summary of how that works.

Most plants are perennials, meaning that they do not have a fixed lifespan.

As you may vaguely remember from your high school biology class, animals age through mechanisms like somatic mutation, shortening of telomeres, and accumulating costs of repair maintenance.

Plants, on the other hand, are not significantly affected by these mechanisms which typically result in fixed lifespans for animals. Instead, their deaths are mostly determined by external factors rather than genetic factors. That’s why they’re able to live so long and why their lifespans are undetermined.

If you’re really interested in learning more about that, I found a couple of good scientific literature review papers that you can read here and here.

Common reasons why a terrarium dies

So now that we know theory and practice, what are some of the common causes terrariums die?

Most terrariums die because they are getting too much or too little of the things they need to survive like:

The most common culprit for an unhealthy terrarium is overwatering. When you give your plants too much water, you are essentially depriving them of oxygen by smothering their roots with water. Plants need oxygen to perform respiration and break down sugars into energy.

It also leads to problems like mold growth and root rot.

A lot of people want to give their terrariums a whole bunch of “love” by giving them plenty of water. That’s actually going to do more harm than good because terrariums typically don’t need too much water, especially compared to your common houseplant.

I have another blog post on that exact subject that you can check out here.

The second most common mistake is when people place their terrarium in a location with inadequate lighting conditions. Too much light can actually heat up your terrarium and kill off your plants while placing them in the shade is going to deprive them of light for photosynthesis.

Ideally, your terrarium should be placed in indirect light for the best results.

If you’ve got the lighting and water down, that’s probably 90% of what you need to do to have a healthy terrarium.

Soil nutrition is the last issue I can imagine people having with their terrarium. Over time, the nutrient content can be depleted, causing your plants to start dying out. It can also happen if there weren’t any nutrients to begin with (see my results with the moss experiment).

That one you might not catch until a few years down the road, once your plants have tapped into most of the nutrients available in your terrarium.

If you have all of these conditions correct, your terrarium will likely last for many decades or more. In fact, the oldest known terrarium is coming up on 60 years old. And that one hasn’t been opened in several decades.

So who knows, your terrarium might see similar results and last you for the rest of your life.

I hope that answers your question, if you want to learn more about terrariums, check out some of the articles below.

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