How to Keep Humidity in a Glass Terrarium

Terrariums are generally low-maintenance. Because the plants and the soil in terrariums release water vapor, they essentially recycle the water it produces. If sealed, terrariums can be self-nourishing. 

Regardless, it’s important to know how to keep humidity in a glass terrarium so you can grow all kinds of exotic plants (and even animals) inside these glass enclosures. 

In this article, I’m going to be breaking down all the ways we can effectively trap humidity inside a terrarium. Whether you’re domineering over a sealed or unsealed terrarium, this information is going to be valuable to you.

What are Terrariums? 

Terrariums are small, enclosed living spaces for certain plants, amphibians, and insects like crickets and tarantulas. They’re also commonly known as glass gardens, Wardian cases, or vivariums.

Choose the best terrarium housing here.

They may be used for decoration, plant or animal propagation, and/or scientific observation. Think of them as an indoor garden, or a mini-greenhouse. 

These glass enclosures mostly come in two types: sealed and open. Sealed terrariums have a removable lid, similar to that of dome terrariums, while the latter doesn’t. 

Top 5 Tips to Keep Humidity in a Glass Terrarium

Without enough humidity, your ecosystem may not thrive. Therefore, it’s important to have just the right amount of moisture inside your terrarium, so your plants and animals live to their fullest under your care. 

Increase Temperature 

The easiest way to increase terrarium humidity is to create an environment with warm air. When properly regulated, heat makes the water inside the glass enclosure evaporate quicker and subsequently turn it into water vapor. 

Depending on where you live, there are a number of ways to increase the temperature in your terrarium. 

1. Increase the temperature of your central heating system to warm up your terrarium. Doing so will balance condensation levels by equalizing temperatures across the glass.
2. Place your terrarium in a place where there’s natural light. Remember not to put them in direct sunlight, however, as the sun might burn the plants aided by heat of the glass. 
3. If your room is particularly cold, or if it’s winter-time where you live, you can purchase a heating mat so you can put the terrarium on top of it. It’ll work particularly well if you have a drainage layer at the bottom of your terrarium.

Increase Water Levels 

Without sufficient water, especially when combined with your terrarium’s heat, your plants will inevitably dry and wither. Therefore, in order to increase the humidity inside your terrarium, you can use the misting method. 

For Standard Terrariums 

For standard terrariums, you can fill up a spray bottle with clean water and mist the inside. Doing so will add to water vapor into the enclosed place and increase humidity. 

My favorite spray bottle to use is the Vivosun Garden Sprayer because you don’t have to repeatedly push the handle to spray water. Instead, as it’s controlled by a hand pump that increases the device’s pressure, water is sprayed by holding down a button. 

For Big Terrariums 

If you own a sizable terrarium and you’re using it to house amphibians like frogs, newts, salamanders, and the like, the best and most convenient way to add mist is by installing an internal misting system. 

Once this system is set up, you won’t have to manually moisten the terrarium yourself. Simply clip the nozzle to the enclosure’s lid, run the hose to the water tank, and let it do the work for you. 

Use Moisture Retaining Substrates

Terrarium substrates that have high water retention properties can significantly boost your terrarium’s ambiance and humidity. 

The substrate you should use depends on the species you’re keeping inside the terrarium. Most species like coconut coir, sphagnum moss, and cypress mulch have high capacities to hold moisture. They also release said moisture in a more or less timely matter. 

If you do decide to use substrates, I highly recommend you add a drainage layer, also known as a “false bottom.” It’s especially useful when you’re housing tropical pants. 

Other than creating a supply of water to saturate the air, drainage layers also: 

• Reduce the risk of oversaturation by allowing water to drain effectively, therefore preventing roots from rotting
• Fuel the water cycle by facilitating the flow of water around the terrarium
• Balance any overzealous watering issues by the buffer it provide 
• Prevent substrate from becoming soggy

Keep in mind that the depth of the substrate matters, too. If you add too little, it won’t increase the humidity in your terrarium. Add too much, and it may become oversaturated and cause molds to grow. A good substrate depth is about 3 inches. 

Add More Plants 

The water cycle won’t be complete without plants. Remember, the more plants you have, the more transpiration it creates. As a result, water evaporation is increased. Thus, more plants = higher humidity levels. 

Interested in what plants you can include in your self-sustaining ecosystem? Learn all about the best terrarium plants here.

Understandably, some of us don’t stuff our terrariums to the brim with plants, especially if we’re going for a particular aesthetic. In such cases, you can use moss. Due to its large surface area and density, it can increase your terrarium’s biomass without sacrificing too much space. Want to learn about moss terrariums? Check out this whole guide on the topic.

If you’re too cool for moss though, consider edible terrarium plants. There are more options than you would think. Carnivorous terrarium plants are more difficult to care for, but have an awesome aesthetic and most fare well in either of the terrarium conditions.

Decrease Air Circulation 

Generally, air circulation isn’t a bad thing. In fact, sufficient ventilation is necessary for the living organisms in your terrarium to survive. 

However, too much air circulation can dry up your terrarium and decrease overall humidity. Those who own closed or sealed terrariums won’t have an issue with air circulation as it’s already sealed from the above. 

But, if you own an open terrarium, decreasing the ventilation is the best way to retain humidity. After all, how can you generate humidity if there’s nothing trapping it inside the enclosure? 

Controlling the ventilation around your terrarium is fairly easy. Simply cover half of the screen lid with some sort of barrier, i.e., a sheet of glass, plexiglass, or other water-proof material.

Final Thoughts on Terrarium Humidity

Retaining the moisture in a glass terrarium is essential if you want your plants to thrive. So, keep your terrarium under suitable temperatures, mist it ever so often, and use moisture-retaining substrates. Remember too that if a terrarium plant does bite the dust, then you can purchase a high-quality replacement online.

As long as you’re doing all three, plus the tips discussed above, you won’t ever have to worry about your terrarium’s humidity!