What extra items can you put in a terrarium?
A terrarium is more than just plants in glass. Many people like to personalize their miniature ecosystem with decorative elements such as stones, figurines, wood, crystals or even sentimental objects. While this can make your terrarium unique, not everything belongs inside a closed environment. Because a terrarium is a living ecosystem with limited airflow and controlled moisture, every item you add influences the balance. In this guide, you’ll discover what you can safely place inside your terrarium, what to avoid, and how different materials affect plant health.
Understanding the terrarium environment
Before adding decorative items, it’s important to understand how a terrarium functions. In a closed terrarium, moisture continuously circulates. Water evaporates, condenses on the glass and drips back into the soil. This creates high humidity and minimal airflow. In an open terrarium, moisture escapes more easily, but drainage and soil balance remain crucial. Any object placed inside will interact with this environment. Some materials hold moisture, some release chemicals and others may start to rot.
Safe items to add to your terrarium
Natural stones and pebbles
Natural stones are generally safe and visually appealing. They do not decompose and can help stabilize the landscape design. However, avoid limestone or rocks that may alter soil pH over time, especially in closed terrariums.
Miniature figurines
Small decorative figurines made of sealed resin or ceramic are usually safe. Make sure they are waterproof and do not contain exposed metal parts that could rust in high humidity. Always clean them before placing them inside.
Treated friftwood
Certain types of treated driftwood can be used, but untreated wood may rot or develop mold in a humid closed terrarium. Wood works better in open terrariums with lower humidity.
Crystals
Most natural crystals are safe as decorative elements. However, avoid soft or water-soluble minerals, as constant moisture exposure can cause deterioration.
Items you should avoid in a terrarium
Organic materials that rot easily
Fresh leaves, untreated branches, cardboard, fabric or paper should never be added. These materials decompose quickly in humid conditions and promote mold growth.
Metal objects
High humidity causes rust. Rust can stain the soil, damage roots and create an unhealthy environment for plants.
Painted or treated decorative objects
Objects coated with unknown paints or sealants may release chemicals into the soil, especially in a closed system where airflow is limited.
Scented items
Artificial moss sprays, fragrance elements or decorative potpourri should never be placed inside a terrarium. These interfere with the natural ecosystem.
What works in a closed terrarium?
Closed terrariums require extra caution. Because moisture remains trapped inside, materials must be resistant to rot and humidity. Safe choices include sealed ceramics, natural stone, glass elements and waterproof figurines. Avoid porous materials that absorb water. Even decorative sand layers must be applied correctly to prevent compaction and drainage problems. Keep decorations minimal. Overcrowding reduces airflow between plants and increases the risk of mold and fungal issues.
What works in an open terrarium?
Open terrariums offer more flexibility. Since air circulates freely, certain decorative wood elements or larger stones work better here. Succulent arrangements often include decorative sand, gravel or sculptural stones for visual impact. However, drainage remains essential. Decorations should never block airflow around plant stems or trap water around the roots.
How decorations affect plant health
If an item blocks light or airflow, it can create micro-areas where mold develops. If it traps water at the base of plants, root rot may occur. Always leave enough space for plants to breathe and grow naturally. Every added object influences:
- Moisture retention
- Airflow
- Soil balance
- Light distribution
- Root space
When less is more
A common mistake is over-decorating. While terrariums can look magical with added details, the plants should always remain the focus. A well-balanced ecosystem with subtle decorative accents is healthier than an overcrowded miniature scene. If you want to refresh your setup properly, make sure your drainage layers and soil structure are still functioning well. A stable base of hydropallets and activated carbon supports both plant health and decorative stability.
