How to Decrease Humidity in a Terrarium (And Keep It Down)

💡 How to decrease excess humidity, and prevent it from happening, in both closed and open terrariums in a few simple steps.

Terrariums, especially closed terrariums, have inherently high humidity. But it only becomes a problem once it gets excessively high and causes things such as mold growth, fogged glass, and worst of all root rot.

To decrease humidity in a closed terrarium simply open it periodically and let the humidity escape. For an open terrarium, just decrease the watering frequency and the humidity will go down. Less water will always result in less humidity.

But keeping it down and preventing it from happening in the first place is always better than having to deal with it once it starts causing problems. The rest of this article will teach you how to control humidity before it gets out of hand, and exactly what to do when it does.

Decreasing Humidity In a Closed Terrarium

The most common cause for excessively high humidity in closed terrariums is a bad initial setup, and overwatering. Overwatering is something that most terrarium builders fall victim to, myself included.

The only way to get rid of the excess humidity is to open it up and wait. Some terrariums will need to be aired more often than others because of the shape of the container. Glass bottle terrariums for example have a very narrow neck, and will need to be aired more often and for longer to get rid of excess humidity. A fish bowl terrarium for example would only need the lid a handful of times.

For next time, when in doubt always water less. And always use a spray bottle and never water directly.

Decreasing Humidity In an Open Terrarium

Decreasing humidity in open terrariums is as lot simpler than closed terrariums and it just comes down to less frequent watering and a temporary change in temperature.

Humidity and high tempoeratures go hand in hand. If you cool the air inside the terrarium, it will hold less humidity. You can do this by placing the terrarium in a colder room for an hour or two. As far as watering goes, it’s pretty straightforward, less water = less humidity.

A good initial setup, with a drainage layer and an adequate container, will prevent humidity problems from arising. Typically containers with a narrow neck and a lot of plants will retain a lot more humidity than containers with a wide neck.

How To Keep Humidity Down

Once you get the initial setup right, and your terrarium finds a healthy water cycle, you will not need to worry about humidity at all. The moisture inside will stay consistent indefinitley. The trick is to get it right the first time by doing proper watering and a proper set up.

If you are still fresh with building terrariums, don’t overthink these things. You’ll inevitably make mistakes. Everybody does. You’ll get the hang of it after a few terrariums as long as you are attentive and observant. Some general advice would be to do a bit of research about the plants you use. For example:

• Mosses thrive in high humidity, so putting them in a closed terrarium with a humidity retaining soil, like clay based soils, is ideal
• Succulents on the other hand don’t like high humidity, so you should only place them in open terrariums
• Plants that have root systems and and at the same time like high humidity, like the polka dot plant, require a drainage layer in your terrarium so that the roots don’t drown

And so on. You get the point. A little research can mean a lot.

Conclusion

Now you know how to decrease the humidity in both open and closed terrariums alike. It’s fairly simple and easy to do, but it can still be a headache, especially if you overwater the substrate.

The best way to lower excess humidity is to avoid it altogether following the steps we talked about. If you do make a few mistakes, don’t overthink it and don’t stress over it. Messing up is a part of building terrariums (wish it wasn’t).

Good luck, and happy terrarium building!