Closed terrariums are ideal for plants that thrive in high humidity and indirect light. Ferns, mosses, nerve plants (Fittonia), and small varieties of begonias and peperomias are excellent choices. These plants love the moist, warm environment a closed terrarium provides.

The watering needs depend on the type of terrarium and the plants within it. Closed terrariums rarely need watering, as they recycle water through condensation. Open terrariums with succulents or cacti require watering every 2-4 weeks, or when the soil completely dries out. It’s crucial to avoid overwatering to prevent root rot.

While regular potting soil can be used, it’s not always the best choice due to its propensity to retain moisture, which can lead to mold and root rot in a terrarium environment. For most terrariums, a mix designed for succulents or cacti, which drains well, is preferable. Adding charcoal to the mix can help filter the soil and prevent mold growth.

Preventing mold involves ensuring proper soil drainage, avoiding overwatering, and providing adequate ventilation, especially in closed terrariums. Using activated charcoal in your soil mix can also help prevent mold growth by absorbing excess moisture. If you notice mold, remove the affected parts and improve air circulation to the area.

Terrarium plants typically require very little fertilizer. If you do choose to fertilize, use a diluted, balanced liquid fertilizer sparingly, and only during the growing season (spring and summer). Over-fertilizing can harm the plants and promote excessive growth, which is undesirable in the confined space of a terrarium.

The amount of light needed varies by plant species. Most terrarium plants prefer bright, indirect sunlight. Direct sunlight can be too intense, leading to overheated terrariums and burnt plants, especially in closed containers. A spot near a window with filtered light is often ideal. For terrariums placed in low-light areas, artificial grow lights can provide necessary light without the risk of overheating.