Most plants grown in a closed terrarium have adapted to thrive in humid conditions. Therefore low humidity can have negative effects on the health of the plants and the overall ecosystem. That’s why it’s important to keep monitoring the terrarium moisture levels and adjust as needed.
On the other hand, excess moisture is potentially damaging. High humidity can provide a favorable condition for the growth of mold in the terrarium. A dense condensation on the walls or lid of a terrarium can also lead to the formation of water stains which may obstruct visibility and the penetration of light.
The quickest way to check for humidity in a terrarium is by observing the condensation on the glass. If water droplets are forming, you can assume that your terrarium is humid enough. If you want exact figures, you’re going to need a thermometer hygrometer.
Signs of low humidity in the terrarium
Clear glass is commonly the first sign of low humidity levels in the terrarium. The plants may also exhibit abnormal appearance including wilting, leaves dropping or browning at the edges, and generally stunted growth. If you have moss, it may become brittle and discolored.
In extreme cases of low humidity, the soil in the terrarium may become excessively dry, leading to visible cracks on the surface. Even if you water the terrarium regularly, if the humidity is low, the moisture in the soil may evaporate quickly resulting in dry soil.
How to increase humidity in a terrarium
Most terrarium plants prefer humidity levels above 50% while others as high as 80%. If you are certain that your plants are craving more, there are several ways to increase humidity in a terrarium.
1. Increase watering
Watering terrarium plants is a delicate balance but a quick way to boost humidity. To avoid underwatering or overwatering, you need to understand the moisture needs of your plants. Tropical plants for example thrive in warm humid environments thus needing regular watering.
Before watering, check the moisture level of the soil. If possible, insert your finger about an inch deep into the soil to feel if it’s dry or moist. If the soil feels dry, it’s time to water. When watering, avoid pouring water directly on the plants as this can lead to mold and other fungal problems.
Pour the water directly onto the soil, aiming to wet the base of the plants rather than the leaves. You may use a narrow-spout watering can or a spray bottle to control the water flow. Ensure excess water is escaping into the drainage layer and doesn’t accumulate in the soil.
2. Seal the terrarium
If you find that your terrarium is not accumulating the desired humidity level then seal it completely. This will stop the moisture from escaping into the open air. When making a closed terrarium, it’s recommended to use a container that has a lid or cover.
Closed terrariums are self-sustaining units that are intentionally sealed to create a constant water cycle. As the plants transpire or the water in the soil evaporates, it condenses on the glass wall and the droplets fall back into the soil. This reduces the need for regular watering.
3. Use a substrate that retains moisture
Using a substrate or soil mix that can hold moisture for longer periods can significantly boost the humidity in the terrarium. Materials like sphagnum moss, coconut coir, or a mixture of peat moss and perlite can help retain moisture while also allowing a proper flow of water.
However, when creating a desert terrarium, its recommended to use soil that sharply drains. Cacti and most succulents are prone to rot when overwatered or grown in excessively humid conditions. That’s why they are best grown in an open terrarium.
4. Add more plants
Placing plants close together can create a microclimate with higher humidity. It is one of the easiest ways to increase humidity for plants without a humidifier. Adding more plants to your terrarium will lead to collective transpiration that contributes to boosting the humidity levels.
However, it is important to understand the moisture requirements of each plant that you intend to add to the terrarium. It’s best to use plants with the same care needs.
5. Use a terrarium humidifier
If the above options are not sufficient for increasing humidity in a terrarium, you can use a small humidifier. When choosing a terrarium humidifier, it’s important to consider the size of your terrarium and the specific humidity requirements of the plants.
It’s also worth considering the ease of use, maintenance requirements, and noise level of the humidifier.
How to lower humidity in a terrarium
If you suspect that your terrarium has excess humidity, you can open the lid to allow in some fresh air. The circulation of air will drive away some moisture. You can also consider reducing the frequency of misting or using a dehumidifier to lower humidity levels.
Cleaning is also important in maintaining a closed terrarium. It is the only way of removing residue and stains on the glass walls for a clear view.
Use a soft cloth or sponge dampened with a mild cleaning solution, such as a mixture of water and mild dish soap, to wipe the interior walls and surfaces of the terrarium. Pay attention to any stubborn stains or residues and gently scrub them away.
Monitoring moisture levels in a terrarium can help maintain a healthy balance of humidity in the plants. Adjusting watering, sealing the terrarium, or using a humidifier are some of the methods to increase humidity in a terrarium.
My name is Diane M Lewik, and I am the founder of this website. I am a degree holder in plant biology from the University of California – Berkeley. Over years, I have cultivated a vast collection of succulents and I have learned a great deal about how to grow and care for these unique plants.