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Save Your Terrarium From Mold!

Everyone hates how mold will destroy a terrarium. It’s all of your hard work, dead and in the garbage. Plus these were your little life forms you been taking care of, sometimes it’s sad to see your green friends die! 

Today we will be going over the conditions that lead to mold growth, prevention methods, and possible ways to save your terrarium, if it’s not too late.


The best thing you can do for yourself when trouble-shooting any problem is to understand the underlying cause or conditions.

Mold thrives on three things: moisture, warmer stagnant air, and low or lack of light

Often times you will find mold in your terrarium if you don’t regularly air it out, have too much plant mass to air, you have it next to a heat source, or it’s too far away from UV light.


There are quite a few ways to prevent moss from getting into your terrarium. The first and most important is: WASH YOUR MOSS! I know you’ve heard us say this before, but we can never overemphasize how important it is! Also please, always quarantine your moss before you use it in a terrarium.

Next, you should never add soil to your terrarium unless you are planning on adding other plants that need soil. This is because organic matter decomposes and can lead to perfect conditions for mold to take hold. Also, often mold spores can be found in soil. 

If you are adding plants that need soil, that’s totally ok! Because you’ll need to be watering your terrarium more frequently for those plants, your terrarium will be getting the much needed movement of air. 

Also, something that can help is adding activated charcoal to your substrate. So say you have soil for your other plants, place a layer of charcoal over the area you plan to place moss in. Don’t mix the charcoal into the soil, while this is good for your soil it will not help keep mold away from your moss in the end.

Another important aspect of building a terrarium is what we like to call: the terrarium golden ratio. In order for there to be enough air inside your terrarium to keep mold away and for your plants to thrive, you need at least half of the terrarium to be air.

Please don’t over plant your terrarium! I know some of you may have seen some of those beautifully done designs by @dbterrariums (Doodle Bird Terrariums).

They know what they’re doing!

It may seem like they’re putting in a lot of plants into their terrariums, but their terrariums are actually quite large most of the time. If you look closely at their designs you’ll see they have the golden ratio of plant mass/substrate to air. 

Sometimes they’ll even use less than half of the terrarium space in plant mass/substrate!

The last, but definitely not least, step in preventing moss is making sure you frequently air out your terrariums! At least once a week for an hour, if not three or more times a week for 15 to 30 mins. Always make sure you water them before you close them back up again. 


Now I’m sure you’ve been waiting for this section, if you haven’t already skipped down to it. As with treatment of anything: prevention is always better and is your first line of defense. 

But here are some ways you can remove mold from your terrarium. 

If your terrarium is just starting to show signs of mold in one secluded area you can do one of two things: 1) remove the affected area. 2) take multiple cotton swabs and get them wet. Then wipe off the mold, with each wipe use a new cotton swab. While this may help the situation, it's not a guaranteed solution.

Usually you’ll need to do more extensive sterilizing methods. 

First if you have any “hardscapes” like rocks or wood to add design elements to your design, remove them from the terrarium. Place the wood or any other “delicate” objects in a diluted solution of bleach and water. Let soak for a few minutes. For the rocks and “hard” objects, use a stronger solution of bleach and water and let soak longer. Then place everything to dry, so the bleach can evaporate.

Wipe off affected glass in terrarium with a really diluted water and bleach. We recommend bleach to disinfect because it is the most effective disinfectant without dealing with more harsh chemicals. I suppose you could use tea tree oil, but we have yet to try that method. 

Next, replace affected substrate. Make sure to add more charcoal around the mossy areas. 

Finally the one fungicide product we recommend is Neem oil. Actually Tanner’s professor (yeah Brother Nelson!!!) was on the team that developed this product. It’s an all natural oil spray that is an effective pesticide. It essentially smothers mold and other pests while still allowing the plants to breath. It’s completely safe to use and has no harmful chemicals, just all natural ingredients. 

Now comes the saddest part of this post: what if the terrarium is just too far gone to save. Well, we hate to say it, “We’re calling it. Time of death: 6:00 pm (insert month, date, and year you’re reading this article).” 

The best thing to do now is to dump everything out, determine what “hardscapes” you’ll salvage, and disinfect those and your glassware. 

Sorry my friend! Try again, and this time you can use your new found prevention methods. If you need more moss, please feel free to pick up one of our grab bags

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Thanks again for checking us out. We hope this post has been helpful! Please feel free to share on social media. In fact we’d really appreciate it if you did! 😊

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