Anytime you build a terrarium, you’re going to need to add water. That begs the question, where does that water go once you close the lid?
In other words, are terrariums waterproof? They don’t necessarily have to be completely waterproof. It can even be beneficial to have small openings to prevent overwatering and to allow for air circulation within the terrarium. On the other hand, a waterproof terrarium can reduce the need to re-water the terrarium by maintaining a constant level of water to circulate within the container.
There’s no sweeping generalization you can make here about the “best” type of terrarium. However, the type of container you decide to go with will be based on your individual preferences for certain pros and cons.
Waterproof vs. Non-waterproof Terrariums
Another way we can think about the waterproof and non-waterproof distinction is through the lens of open and closed terrariums.
You can think about an open terrarium as a bunch of plants in a pot. There’s a large opening exposing the plants to the open air and direct sunlight.
On the other hand you have closed terrariums. You can imagine these as plants sitting in a completely sealed jar.
For the purposes of this article, I’m going to assume we’re talking about waterproof and non-waterproof closed terrariums because that’s where you’re going to see the differences. Functionally speaking, waterproof and non-waterproof open terrariums will be pretty much identical aside from one allowing water to leak out of the container.
Here’s a table listing out some of the key differences between a waterproof and non-waterproof terrarium:
| Waterproof Terrarium | Non-waterproof Terrarium | |
| Pros | Less need to re-water since water stays in the systemMost containers (jars, jugs, bottles) are already waterproof by default | Resistant to over-wateringFresh air can circulate within the system |
| Cons | Prone to over-wateringIn some cases, sealant may be required for tanks with leaks | May require more check-ups to make sure there’s enough water in the terrariumAdditional setup may be required to create appropriately sized openings to allow for drainage |
If you look over the pros and cons, one thing you’ll notice is that some of the points listed under non-waterproof terrariums are similar to the characteristics of an open terrarium.
Conceptually speaking, you can think about a closed terrarium with a few small openings as a hybrid between an open and closed terrarium. Really the only difference between a non-waterproof closed terrarium and an open terrarium is the size of the openings through which water can escape.
Because of this, non-waterproof closed terrariums share the low maintenance requirements of a closed terrarium while at the same time being more resistant to over-watering issues characteristic of open terrariums.
In that sense, having a container that is not waterproof can actually be beneficial for your terrarium plants.
But going from completely sealed to not completely sealed does have its tradeoffs on the maintenance side of things. If water is slowly leaving the system, that’s going to require more frequent watering of your terrarium (which may not be a huge deal for some people). On the same note, there’s also going to be a need for more checkups to make sure the water level is good.
How do I tell when I need to water my terrarium?
There’s a few signs you might want to watch out for that might indicate a need to add some water to your terrarium:
- Crispy, wilting, yellow or brown leaves
- The substrate feels dry when you touch it
- You stop seeing condensation in the terrarium in the mornings/evenings
If you’re seeing some of these signs in your terrarium, it might be time to add some more water to the system.
Preferably, you would mist your plants with dechlorinated water, but it shouldn’t kill your plants to just pour a little tap water in there. Just be very careful to not overwater the terrarium.
If you want to revive some plants that seem very dried out, you can try taking them out, soaking them in water for 30 minutes, and letting them dry before adding them back in. A quick rinse could be worth a shot as well.
I wish I could tell you “add 25 ml of water when the humidity drops to 10%”, but unfortunately this is something that’s going to take a little bit of intuition and experience. Even if you did measure things like humidity and water volume, the optimal conditions for your specific terrarium ecosystem would vary depending on the type of plants you have in your terrarium.
How do I make a leaking terrarium waterproof?
If you have a terrarium that has some undesirable leaking, you always have the option of waterproofing your container with sealant.
Some popular options to do this are silicone sealant, polyurethane, and epoxy. These sealant materials basically fill in the cracks with water-resistant rubber-like material so water can’t escape.
Here’s a rough outline of how you would apply sealant to any leaks:
- Clean the area with rubbing alcohol
- Air dry
- Seal the seams
- Smooth the sealant into the edges
These instructions might vary depending on what type of sealant you’re using. So always refer to the instructions that come with the sealant package or browse youtube for tutorials.
Whenever you apply sealant, it’s also important to consider how the area will look in the end. You definitely don’t want to have glaring white smears all over your terrarium that detract from the beauty of your terrarium.
To get a very clean look, you’re going to want to put some masking tape around the area to keep the edges sharp and in a straight line. You’ll also want to pull the cartridge toward you as you squeeze out the sealant to get a nice, even application.
Ideally, you would discover the undesirable leaks before adding plants into your terrarium. However, if you’ve discovered them after getting everything setup, you will want to double check to see if your sealant can be applied to a wet surface. Otherwise, flex tape or flex seal should work just fine (although it might not be visually appealing).
How do I avoid overwatering my terrarium?
While giving your plants enough water to last a lifetime might seem like a good idea, that’s actually going to do more harm than good.
Overwatering your plant could cause plant roots to rot and allow mold to start growing. Some telltale signs of an overwatered terrarium include:
- yellow, wilting leaves
- soggy substrate
- rotten smell
- Significant water pooling at the bottom.
A healthy terrarium should have these characteristics:
- Green, crisp leaves
- Moist substrate
- A fresh, garden-like, earthy smell
One method to avoid overwatering is to include a false bottom in the terrarium. A false bottom is essentially a drainage layer that collects water that passes down the substrate. It’s basically a way to prevent water from pooling around the roots, causing them to rot.
The false bottom typically consists of a 1-2 inch layer of rocks, activated carbon, charcoal, or sand. It could even include synthetic materials like marbles or bath beads. The key to this layer is it allows water to easily pass through to the bottom of the container, flowing/draining the water away from the substrate.
Often, a mesh is added between the false bottom and the substrate to block the roots from growing into the false bottom layer. Most material will do as long as it won’t degrade in water over time and allows water to flow through while blocking roots from growing deeper.
You could buy garden mesh on Amazon for a few bucks or you could make your own DIY mesh by grabbing some plastic bags or empty cereal bags, cutting out the shape of your terrarium, and poking some holes to allow water through.
When cutting out the shape, make sure to cut out a shape slightly larger than your terrarium so that it curls up around the edges, preventing the plant roots from reaching around the side into the false bottom.
If you have a false bottom in place, your plants should be safe from overwatering so long as the water level in the false bottom does not reach the substrate and the roots don’t reach into the false bottom.
Conclusion
So are terrariums waterproof? They can be, but don’t have to be. A waterproof terrarium will mean less maintenance, but will require more caution to avoid overwatering. A non-waterproof terrarium will require a little more maintenance, but will be more resistant to overwatering.