Terrarium Troubles: The Real Reasons Behind Mold Growth

Mold growth in terrariums can be frustrating, but there are a few common reasons behind it. Here are some of the real reasons why mold may be growing in your terrarium.
A closed terrariums.

Terrariums are more than just a delightful piece of nature tucked into your living space; they’re an escape into a world of wonder and tranquility. As you gaze into the lush greenery and observe the delicate balance of life thriving within, it is easy to see why terrariums have captured the hearts of many succulent enthusiasts. However, terrariums are not without their challenges. One of the most common issues is mold growth. In fact, mold growth can be a frustrating problem that threatens to disrupt the delicate balance of your wonderful ecosystem.

So, why does mold grow in terrariums? There are several key factors at play. Excess moisture is often the primary culprit, creating the perfect breeding ground for mold spores to take hold and flourish. Poor ventilation, improper temperature, lighting conditions, and overwatering can also contribute to mold growth. Other causes include poor drainage, improper cleaning, inappropriate terrarium design, and decomposition of organic matter.

This blog post delves deep into the fascinating world of terrariums and explores the real reasons behind mold growth. Read on to learn more.

Understanding Mold Growth

Mold is a type of fungus that can thrive both indoors and outdoors. It is an essential part of a natural ecosystem since it helps to break down organic matter, returning nutrients to the soil. Despite its role in nature, mold growth inside terrariums is usually unwelcome.

Mold reproduces via microscopic spores, released into the air and spread by wind, water, or animals. When the conditions are right, these spores enter terrariums and begin to grow, forming unsightly colonies of fuzz and mold.

A terrarium
Despite its role in nature, mold growth inside terrariums is usually unwelcome.

Mold colonies can spread quickly, depriving plants of oxygen and nutrients for healthy growth.

The Real Reasons Behind Mold Growth

So, what causes mold growth in terrariums? The truth is that several factors can contribute to mold growth in a terrarium. Below are some of the top reasons for mold growth in terrariums:

1. Excessive Moisture

    Excessive moisture is a crucial factor contributing to mold growth in a terrarium. Remember that a terrarium is a closed or semi-closed environment mimicking a miniature ecosystem, consisting of a transparent container, plants, soil, and sometimes additional elements like rocks or decorative items.

    The terrarium’s water cycle plays a crucial role in maintaining the balance of the ecosystem. Moisture is usually introduced into the system through watering or misting.

    As the terrarium absorbs heat and receives sunlight, the moisture evaporates and rises within the container.

    Upon reaching the cooler upper walls or lid, the warm, moist air condenses back into water droplets, drip down to the potting mix and plants, completing the water cycle.

    The biggest contributor to excessive moisture in a terrarium is overwatering since it leads to saturated soil and waterlogged conditions. The excess water may not evaporate efficiently, causing prolonged high humidity.

    A jar converted to a closed terrarium.
    As the terrarium absorbs heat and receives sunlight, the moisture evaporates and rises within the container.

    Moreover, limited ventilation can also trap the moist air inside the terrarium, preventing its escape and leading to humidity buildup. Maintaining optimal moisture levels in the terrarium can be challenging in regions with high humidity.

    Excessive moisture will always lead to mold growth issues. Mold spores, naturally present in the environment, thrive in damp conditions.

    Excessive moisture provides an ideal breeding ground for the spores, leading to unsightly and potentially harmful mold growth on terrarium plants and surfaces.

    Proper care and maintenance practices are essential to prevent excessive moisture and mold growth in a terrarium. Water wisely and be mindful of the water needs of your plants and terrarium size.

    Allow the potting mix to dry between watering sessions and provide proper ventilation. Ensure the terrarium has adequate airflow. This can be achieved by periodically opening the lid to allow fresh air circulation and excess moisture to escape.

    2. Poor Ventilation

    Ventilation is another important factor that contributes to mold growth in terrariums.

    Warm moist air will get trapped inside the closed environment without adequate air circulation, leading to humidity buildup and mold growth.

    It is essential to ensure your terrarium has enough ventilation. Open the lid periodically to allow fresh air circulation and excess moisture to escape.

    A closed terrarium on a shelf.
    Ventilation is another important factor that contributes to mold growth in terrariums.

    Provide extra ventilation by creating small openings in the container walls or lid for improved air circulation.

    3. Organic Matter Decomposition

    Organic matter decomposition is another significant cause of mold growth in a terrarium. Various organic materials naturally occur within the terrarium ecosystem. These materials include fallen leaves, flowers, or plant debris that undergo a natural life cycle.

    With time, organic materials break down into simpler compounds through decomposition.

    The decomposition process involves the activity of microorganisms such as bacteria and fungi, collectively known as decomposers.

    They feed on the decaying organic matter, breaking it down and releasing nutrients into the soil.

    Mold and fungi are crucial in decomposition because they are the primary decomposers responsible for breaking down plant matter.

    Mold spores, abundant in the environment, can find their way into the terrarium and settle on the decaying material.

    When organic matter, such as dead leaves or flowers, accumulates in the terrarium without being removed, it provides an abundant food source for mold.

    The moisture present in the decaying material further facilitates mold growth since mold thrives in damp environments.

    Once mold establishes itself on decaying organic matter, it can quickly spread to other surfaces in the terrarium.

    The spores become airborne, settling on plants, soil, and other decorations. This leads to the further expansion of mold colonies.

    4. Incorrect Light and Temperature Conditions

    The light and temperature conditions in your terrarium can also contribute to issues with mold growth.

    Incorrect lighting or temperature levels can cause excessive moisture to remain trapped inside the terrarium, furthering the ideal environment for mold spores to thrive.

    A open terrarium outdoor exposed to sunlight.
    Check the temperature regularly and ensure the terrarium doesn’t become too hot or cold.

    Ensure your terrarium is placed in a location with bright but indirect light sources.

    If your terrarium is exposed to direct sunlight, it can heat up quickly and cause water to evaporate too quickly, leading to waterlogged conditions and mold growth.

    The terrarium’s temperature should also remain within optimal levels for plants in your system. Check the temperature regularly and ensure the terrarium doesn’t become too hot or cold.

    5. Poor Terrarium Design

    The design of a terrarium plays a crucial role in its overall health and functionality. Poor terrarium design can create an environment that encourages mold growth and other issues.

    Certain design elements may trap excess moisture or prevent proper air circulation, making the terrarium susceptible to mold problems.

    One common design flaw is inadequate ventilation. Terrariums need proper airflow to prevent the buildup of stagnant, moist air.

    If the terrarium lacks sufficient openings or vents, the trapped humidity can create a favorable environment for mold spores to thrive, leading to mold growth on surfaces and plants.

    Another aspect of poor design is the choice of lid or closure. If the terrarium has a completely sealed lid, it may trap moisture inside, leading to high humidity levels and an increased risk of mold.

    A lady smiling holding a closed terrarium.
    The design of a terrarium plays a crucial role in its overall health and functionality.

    Instead, a terrarium should have a partial lid or openings, allowing air exchange and moisture dissipation.

    The selection of materials also impacts the terrarium’s susceptibility to mold growth. Certain materials may retain moisture more effectively, contributing to higher humidity levels.

    For example, a terrarium made entirely of non-porous materials like glass or plastic can lead to moisture accumulation, making it necessary to take extra precautions in managing humidity.

    6. Improper Cleaning

    Your terrarium requires regular cleaning to maintain its health. Over time, organic debris, such as dead leaves or flowers, can accumulate in the ecosystem and form an ideal environment for mold growth.

    Incorrect cleaning techniques can exacerbate this problem and further promote the spread of mold spores.

    If you use a damp cloth or sponge to clean your terrarium, make sure it is thoroughly wrung out before wiping down surfaces to prevent additional moisture from being added.

    Also, avoid overwatering when cleaning your terrarium since it can cause waterlogged conditions and mold growth.

    Use a dry cloth or paper towel for gentle wipe-downs of the glass walls, decorations, and other surfaces.

    If you find mold growing on any surface within your terrarium, you can get rid of it by scrubbing it with a dry brush or sponge.

    Remove infected plant parts and dispose of them safely to prevent further contamination. Make sure all debris is removed from the terrarium to discourage mold growth.

    7. Use of Contaminated Soil

    Lastly, using contaminated soil can also cause mold problems in your terrarium.

    Unsterilized dirt or compost may contain fungi or bacteria spores that facilitate the development of mold colonies.

    A close round terrarium with succulent.
    The design of a terrarium plays a crucial role in its overall health and functionality.

    Therefore, it is essential to use sterilized soil when planting your terrarium and avoid using potting media that could contain any contaminants.

    To ensure the health of your terrarium, provide optimal conditions for plant growth, and prevent mold problems, it is necessary to check for any signs of mold growth regularly.


    Mold growth in terrariums is a common issue caused by excessive moisture, poor ventilation, and incorrect lighting and temperature conditions.

    Proper care and maintenance practices are essential to providing an optimal environment for your terrarium plants to thrive and prevent mold growth.

    Water wisely according to your plants’ needs, use sterile soil, and clean regularly to prevent the buildup of organic matter. Proper terrarium design is also important for ensuring adequate air circulation and preventing mold growth.

    Ensure you watch for potential signs of mold in your terrarium and act promptly if any issues arise.

    Last update on 2024-02-05 / Affiliate links / Images from Amazon Product Advertising API

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