Terrarium Up Close - Humidity and Condensation

And so..

Throughout the years of our terrarium building journey, the frequently asked questions we got are these, “how do I maintain it?”, “They are self-sustaining, which means no maintenance required, right?”.

Well, terrariums are indeed low in maintenance, but they are in no way “no maintenance”.  This misconception is usually the main cause of failure for many terrariums.

For this segment of our blog post, we will look at 3 crucial aspects in ensuring a healthy and living terrarium. Though we will like to put a disclaimer out there, the points we are about to make in this post are relevant to the terrariums we build here at InOut Atelier. Our terrariums are unique and different from the other terrariums out there. The methods, techniques, materials, botanical selections we use may be different from many other terrariums artists/makers. Thus our advice should be heeded with discern.

The three crucial aspects we are covering are;

1) Humidity and Condensation

2) Light and shade

3) Irrigation

We will be breaking up the post into 3 parts so that it’s easier to digest, and for this post, let’s talk more about humidity.

HUMIDITY AND CONDENSATION

I always share with students of our class that humidity is almost a default and natural occurrence that you should see in your terrarium. This humidity will eventually contribute to the condensation you see inside the terrarium over time. And this condensation when becomes dense will form into water droplets, and they will slide right back into the substrate once they are heavy enough. Hence, creating the concept of a self-sustaining ecosystem that made the terrarium so popular.  

To understand the concept of how humidity is formed inside the terrarium in the first place. We need to revisit a few basic primary school science.

1) Transpiration

Plants breathe, and they lose moisture to their surroundings, this process is called transpiration. However, in the context of an enclosed terrarium, the moisture is trap inside the jar, unable to escape. This moisture then caused the air to become humid.

2) Condensation

The temperature in a terrarium is usually higher than the temperature outside the terrarium. This is because terrariums are like mini-greenhouses. They absorb light and retains heat. The difference in temperature between the inside and outside of the terrarium encourages water condensation to form when the warm air hits the cold surface and reaches its dew point.

WHAT HAPPENS WHEN THE CONDENSATION IS REALLY THICK AND DENSE?

Even though humidity and condensation are really important for the longevity of your terrarium. Too much of them will affect the mosses and also impair the visual interest of the terrarium as well. And they can be off-putting considering after spending all that money to buy/build one to decorate your space, only to end up with a bob of dense water vapor that doesn’t seem to go away.

If that is the case, you might have too much moisture in your terrarium which could be due to overwatering. But regardless, there are ways to mitigate that.

#1 Leaving the terrarium lid slightly ajar

This will allow for some ventilation into the terrarium, and an opportunity for the excessive vapor to evaporate, thus balancing the humidity level in the terrarium. The ventilation also helps to regulate the stagnant air that was previously in the terrarium too.

Bearing in mind that by doing so, you are allowing moisture to escape the terrarium. This means you will have to pay closer attention to the mosses and ensure that they don’t dry out. Replenish the moisture by watering when needed. (do check back as we discuss on the topic of irrigation in the next few posts)

“So how long should we leave the terrarium lid ajar?”

I know you’re asking that and we’re not going to leave you hanging.

Just leave it ajar until you don’t see as much condensation will do. Or, when the condensation is at a level that doesn’t bother you anymore. The whole idea is to have a good view without compromising too much on the moisture level.

Just a gentle reminder, don’t forget to close the lid. Coming from experience.

#2 Wipe the inside of the terrarium glass

This is probably the most intuitive method, but by doing so, you are permanently removing the moisture from the terrarium. And it can also be pretty laborious when you have many terrariums around the house at the same time. We don’t normally practice this method unless we need to remove the moisture quickly for a photo shoot. So unless you have a guest coming and you want it to look presentable, we suggest you follow the first tip instead.