Closed terrariums are typically easy to care for than potted plants. Since they are enclosed, they recycle moisture and this reduces the need for watering. However, they require regular monitoring for moisture levels, pruning to control plant growth and occasional cleaning of the glass.
The first step in creating a low-maintenance closed terrarium is to choose plants that thrive in humid and low-light conditions. Mosses, ferns, and small tropical succulents would make great plants for this moist and shaded ecosystem.
Further, I recommend you use a well-draining soil mixture suitable for the plants you have chosen. The addition of pebbles or gravel layer at the container bottom is also beneficial in facilitating proper drainage. This is a key requirement in both closed and open terrariums.
How to care for a closed terrarium
Taking proper care of your terrarium is important for the health of the plants within. It is also a way of adding more life and glamor to the system.
Here are important care guidelines to follow:
1. Provide appropriate lighting
Place your terrarium in a location with bright indirect light. The plants enclosed in the container will need at least 4 to 6 hours of sunlight each day to remain healthy. As you know, green plants need solar radiation to make their own food through photosynthesis.
Without light, your terrarium plants will grow spindly, pale, and even wilt and die due to a lack of sugars. However, avoid placing a closed terrarium in direct sunlight, as it can cause excessive heat buildup and potentially harm the plants inside.
If your home or office is not receiving sufficient natural light you can introduce artificial grow lights to supplement the lighting requirements of your terrarium.
2. Watch for humidity
While closed terrariums are designed to be self-sustaining, recycling moisture within the container, it is important to monitor humidity levels. Excessive condensation on the glass can cause mold in the terrarium. In such a case, remove the lid for a short period to allow some air that will drive out the moisture.
On the other hand, dryness in the system can cause plant dehydration and wilting. If the terrarium glass is ever clear, it means your plants need some watering. You’ll need a small hygrometer to know the exact moisture level in your closed terrarium.
3. Balance the watering
A completely enclosed terrarium needs no watering, but water a little if the soil is dry and the plants are showing signs of wilting. However, NEVER pour water directly into the plants as this can result in overwatering. Terrariums have no drainage holes and typically there is nowhere excess water can go.
When watering terrarium plants, use a misting bottle to add a little water at a time. DO NOT water if there are some droplets of condensation on the glass. This typically shows that the moisture is being recycled and everything is healthy.
4. Introduce isopods or springtails
The addition of isopods and springtails in the terrariums can be helpful in controlling fungus. As you know, fungus including mold thrives in humid conditions. These beneficial soil microorganisms feed on decaying organic matter, which helps in cleaning the terrarium and stopping the growth of mold.
Springtails and isopods are available at gardening centers and can also be ordered from online retail stores. Add them just a few at a time and keep the jar or container sealed so prevent them from escaping.
5. Provide some ventilation
Although closed terrariums are designed to be sealed, it’s still beneficial to open the lid periodically for a short time like one hour to allow some fresh airflow. This can help prevent excessive buildup of moisture on the glass and leaf surfaces.
Fresh air also provides oxygen which aids in the conversion of food molecules inro to energy for plant growth. It also reduces the growth of powdery mildew and other infections that promote rot.
6. Prune overgrown plants
Plants are likely to shed off some tissues and you may end up with dead leaves and decaying plant materials in the terrarium. This can attract mold growth and promote an unhealthy environment for the plants.
Therefore, regularly inspect your closed terrarium and remove any dead leaves and other decaying plant material. Additionally, prune plants that have outgrown the space to maintain an appropriate size to prevent overcrowding. I recommend you trim the plants during the spring or summer months.
7. Clean the glass occasionally
Over time, you may notice mineral deposits or the growth of mold and algae on the container walls. This is not only visually unappealing but also a threat to your plants. Terrarium glass should remain clear for the best view and proper penetration of the light.
Therefore I recommend you occasionally clean the glass using a soft cloth or sponge dipped in a mild solution of water and vinegar. Do not use harsh chemicals or abrasive materials that could damage the glass or harm the plants.
Terrarium care FAQ
How long can a closed terrarium last?
A properly maintained terrarium can last for an extended period of time, often more than one year to decades. This may depend on the type of plants you grow and the care you provide. My closed terrarium is now 5 years old and the plants aren’t showing signs of bowing down.
Can terrariums survive without sunlight?
Terrarium plants generally require some level of light to thrive. Low-light tolerant plants are likely to survive with lower levels without any problem. However, it’s still important to place a terrarium in a place that receives indirect natural or artificial light for several hours a day.
How often should you water a closed terrarium?
It is important to water the plants a little when setting up a closed terrarium. Thereafter, you can monitor the moisture level and water when the soil feels completely dry. I water my closed terrarium once every 3 months and my plants are healthy.
Why do my closed terrarium plants keep dying?
Plants in a closed terrarium can keep dying due to insufficient light, overwatering or underwatering, poor drainage, lack of ventilation, or pests and diseases. You can save the plants by identifying the underlying issues and making appropriate adjustments.
Maintaining and closed terrarium is pretty simple. If you have grown the right type of plants grown in well-draining soil, just provide adequate lighting, balanced watering, and occasionally clean the terrarium glass. Regular monitoring of moisture levels, pests, and diseases is also needed for your plants to thrive.
DelPrince, J. (2013). Interior plantscaping: Principles and practices. Clifton Park, NY
Hessayon, D. (1998). The house plant expert. London: Transworld Book
The complete houseplant survival manual. North Adams, MA
How to Design a Closed-System Terrarium By James M. DelPrince, PhD, Associate Extension Professor, and Gary Bachman, PhD, Extension/Research Professor, Coastal Research and Extension Center.
Creating a Garden in a Terrarium by Deborah J. Benoit, Extension Master Gardener University of Vermont
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.