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Is My Terrarium Failing? Watch for these 11 signs

Anyone who starts anything new will always have some self-doubt. Building a terrarium is no exception. If you clicked on this article, I’m guessing you’re starting to see some signs in your terrarium that are causing you to worry.

In this post, we will go over 11 different signs that your terrarium is failing. If you see any of these signs in your terrarium, maybe that should cause you to be concerned. It may also give you some ideas on what to look for in the future in case you weren’t aware. We’ll also go over what you can do to save your terrarium according to the symptoms you are seeing.

Soaking wet or bone dry substrate

First things first: you’re going to want to check on the water levels in your terrarium. In many cases, this is the root cause for other symptoms you might see listed down below.

Your terrarium should have moist soil, but not soaking wet or bone dry. The only exception would be If you are growing succulents in an open terrarium. In that case, you actually are going to want to lean towards keeping the substrate dry rather than moist.

The condensation levels in the container will also give you an idea of how your water levels are doing. If there’s a lot of condensation all day long, there’s probably too much water. If there’s no condensation at all, there’s probably too little. You’re going to want to aim for something in the middle with some condensation just at some times of the day.

If you find yourself with too much water in your terrarium, you will have to wipe off the excess condensation and let your terrarium air out for a few hours. Check on the soil periodically and monitor the condensation levels for a few days following to see if any more adjustments need to be made.

If you have too little water in your terrarium, the solution is pretty simple: just add a bit more water. Just be careful not to over water your terrarium.

This is probably the biggest source of failing plant health for most terrarium builders, it’s very easy to make this mistake if you don’t have the experience to tell how much water is enough. If you can get this step right, there’s a good chance that it will solve most of the problems you could be seeing below.

Mold growth

If you start seeing some fuzzy white stuff growing in your terrarium, that’s probably mold. Mold is a fungus that grows when there is a lot of moisture and organic material to digest.

Mold on its own isn’t necessarily going to harm your plants, it’s more of a nuisance than a danger to your terrarium. However, it could be an indicator of other problems in your terrarium.

If you are seeing mold in your terrarium, that probably means that you are overwatering your plants. This is also likely to come up if you don’t have a drainage layer in your terrarium for water to drain away from the substrate.

Ideally, you should take care of this as soon as you can so that the mold doesn’t spread to your other plants and create a bigger mess for you to deal with.

To take care of this, you should first try reducing the water levels in your terrarium. Once the water levels stabilize, the mold should die out on its own. If that doesn’t work, you could try spraying some fungicide around your terrarium to kill it off yourself.

As for preventative measures, you’re going to want to build your terrarium with a drainage layer included if you weren’t doing that already. This allows water to drain away from the substrate, preventing stagnant water from becoming hot spots for mold growth. 

You could also try adding some springtails to your terrarium. You can think of these as small terrarium janitors that eat up mold and decaying organic material. For more info about that, check out this article.

Plant rot

Rotting roots will look black or brown rather than their normal white or yellow color. They’re also going to feel mushy and might fall off your plants at just the slightest touch. Your plant might also feel soft and crumbling.

We’ll talk about this later, but root rot will also be the cause of some other symptoms like yellowing leaves or strange odors.

Root rot is caused by one of two things:

  • Over-watered roots that died from lack of oxygen
  • Fungus that attacks your roots causing them to die

The first one is the most likely cause, with second cause being a potential side effect of the first. If there’s too much water in your terrarium, it’s possible that your plant roots could have suffocated from the abundance of water. It could also happen if your plant roots were sitting in a small pool of stagnant water in the drainage layer or small pockets of water in the substrate.

To double check for root rot, pull your plant out from the substrate along with its roots and see if the roots are black, soggy, and brittle. If you also see any fungus or mold that you didn’t notice, that’s also a secondary indicator of root rot.

If you do see your plants experiencing root rot, all is not yet lost. You might be able to save your plant by removing these rotting parts of the root to stop the spread. 

Grab some shears or scissors to cut off all the affected roots after washing away all the dirt under some running water. If this turns out to be a significant portion of your plant’s roots, you may also have to start pruning your plant leaves. This is going to give your plants a better chance at regrowing because its roots won’t have to provide nutrients to sustain as many leaves.

You could also try dipping your roots in some fungicide to kill off any fungus that’s remaining. If you’re feeling extra ambitious, you can also replace your terrarium substrate entirely to eliminate any remaining fungus or rot that could be just waiting for a chance to spread again.

Unpleasant odors

If your terrarium has an odd odor or smells like rotten eggs, that could be a sign that your terrarium is being overwatered or is experiencing root rot.

If there’s too much water in your terrarium, not only does that promote root rot and mold growth, it could also lead to the growth of bacteria producing these unpleasant odors.

Besides fixing the over-watering situation, addressing the mold or root rot, there’s a couple of other things you can try to get rid of any lingering odors.

You can try adding a little bit of charcoal or activated carbon into your terrarium. Activated carbon is a material that purifies the air and water from toxins and chemicals. By adding a little bit of charcoal to your terrarium, that may help reduce the odors that you’re noticing.

Another more hardcore countermeasure to the odors is to completely swap out the substrate. By doing this, you’re essentially replacing your current substrate containing those odor producing bacteria with completely fresh substrate, hopefully without odors.

Shriveled, crispy, and dry leaves

If you notice that your plant is starting to shrivel and it’s leaves are looking dry, this is a sign that you are not giving your plants enough water. On a related note, your plants could also be getting burnt from too much sun.

The solution should be pretty intuitive: give your plants a little bit of water and see if they revitalize themselves. Just be cautious not to add too much water and end up overwatering your terrarium. As mentioned before, that could lead to a whole host of other issues.

If you notice that your terrarium is getting a lot of sun, you may want to try moving it into a shadier part of your home. If your terrarium is exposed to too much sun, that could be raising the internal temperature to dangerous levels, causing your plants to get baked. This is especially true if you have moss in your terrarium, which are extra sensitive to high temperatures. A closed terrarium is functionally a mini greenhouse after all.

Yellow or discolored leaves

It’s possible yellowing leaves could just be part of the natural aging process. But if you start seeing this happen way too much or to younger leaves, that could be a cause for concern.

Yellow or discolored leaves could be caused by a number of things, including too much sun, over or underwatering, root rot, lack of nutrients, age, or temperature changes. In some cases, it could be caused by using tap water rather than distilled or rainwater.

The first thing you can check is the soil. If it feels very wet or very dry, it’s probably caused by over or underwatering respectively. Once you’ve adjusted the water levels, you might start to see your plants’ leaves turn green again if you caught the issue early enough.

If the problem is related to nutrients, you may want to look into what soil you used for your terrarium with respect to your plants. Certain plants may have preferences for certain soil types. Carnivorous plants in particular require nutrient poor soil. On the other hand, some plants will require a more nutrient-rich soil. It may be worthwhile to do some research to see what plants you have and if your substrate is suitable for your plants.

Sunlight and temperature change may be related. If your terrarium is constantly exposed to direct sunlight with no shading or filtering, the temperature can get pretty hot in your terrarium. It’s possible that the combination of these two things could be the cause of the yellow leaves that you’re seeing. If so, try moving your terrarium away from any nearby windows and into the shade.

Drooping or Wilting leaves

Drooping or wilting leaves is another sign of potential over or underwatering, potentially accompanied by yellow leaves. It could also be due to too much or too little sunlight. In the case of a terrarium, the most likely causes are either too much water or too much sunlight.

Check the soil to see if it’s dry or still wet. If it’s dry, it just needs more water. If it’s wet, your plants roots may be rotting, potentially due to overwatering.

Most likely, if you’ve resolved the sunlight and water situation, your plant leaves should revitalize themselves in a short amount of time.

Strange insects

If you take a look at your terrarium plants and notice that there are really tiny insects crawling around in there (that aren’t springtails), it’s possible you’ve got yourself a pest infestation. This should also catch your attention if you are also seeing other symptoms of poor plant health to go along with this.

Some common pests that you might see include:

  • Spider mites
  • Scale insects
  • Mealybugs
  • Aphids
  • Fungus gnats
  • Caterpillars

If you’ve unfortunately found yourself stuck with some insect pests, you may be able to remove them manually by hand or let them die out on their own by controlling the water levels. If that doesn’t work out, you might have to turn to getting some insecticide sprays.

Exposed roots

If you start seeing your roots appearing at the surface of the substrate or reaching into the drainage layer, that could be a sign that your plant is getting too large for your terrarium.

If your roots are growing into the drainage layer, that’s going to cause some problems with root rot because of constant contact with stagnant water. If possible, you’re going to want to take care of this as soon as you identify it to prevent problems from spreading.

Ideally, this shouldn’t happen if you’ve picked appropriately sized plants for your terrarium with known growth potentials. But if you just didn’t expect your plans to grow this large, you may be able to take them out along with the roots and add them to a larger terrarium.

The other option that you have is to simply trim the roots a bit. Trimming the roots won’t kill your plant, but it will limit the nutrients it will be able to get (which is a good thing for terrarium plants). Aside from getting the roots out of the drainage layer, it’s going to help your plant stay at a relatively small size to fit in your terrarium container.

If possible, stick to removing no more than about a third of the thread roots. If you can, you shouldn’t prune the tap root at all. Instead, focus on separating out the thread roots so that you can focus on trimming those instead. While you’re at it, you can also prune roots that are looking rotted.

Black or brown dots on leaves

If you’re noticing black or brown dots on your plant leaves, you might also see these accompanied with a yellow ring around the spots.

This is possibly a sign of a fungal or bacteria disease that has infected your plant leaves. More specifically, it’s probably a fungus called diplocarpon rosae, also known as black spot fungus. Usually it starts to develop around the springtime when temperatures are around the 60s and plants have been continuously wet for 6 to 9 hours. Once this fungus runs its course, the entire leaf will turn yellow and fall off.

If possible, pluck any affected leaves off your plant and toss them out so that it doesn’t spread to your other plants. To be safe, you might also want to spray down your plants with some fungicide or neem oil. You could also try a mixture of one tablespoon of baking soda with a gallon of water, perhaps with a little bit of horticultural oil.

Pale color and general unwellness

When your plants are looking kind of pale and just generally don’t look very well, it’s possible that your plants aren’t getting enough nutrients. This could happen if your substrate didn’t have any nutrients to begin with (i.e. your substrate is mostly made of coir or sphagnum moss).

Tossing in some nutrient supplements like vermiculite or perlite might be useful for giving your plants much needed energy. If you want a complete do over, you can completely swap out your substrate with native soil, potting mix, or aquarium soil depending on what your plants’ needs are. You could also try applying a solution of liquid fertilizer.

Be careful not to overdo this though. Too many nutrients can also be a bad thing for your plants, especially if you are working with carnivorous plants. Specifically, I would be wary of adding a ton of fertilizer into your terrarium. Having fertilizer in a terrarium could cause your plants to grow a little bit too large for your terrarium container. While seeing plants grow might be fun and satisfying, your plants probably won’t have a good time being crowded against the container walls.

That’s it for the 11 signs, thanks for reading this far. I hope that didn’t scare you off from building anymore terrariums. For the most part, as long as you care for your terrarium properly, you have a very good chance of finding success with your terrarium. And don’t stress if you made a few mistakes here and there or your plants didn’t do so well, it’s all part of the learning process!

Check out some of the articles below if you’re interested in learning more about building terrariums.