Gardening 101: How to Make a Closed Terrarium
A sealed glass world where tropical plants thrive with minimal upkeep and natural charm.
A closed terrarium is one of the most captivating ways to bring lush greenery into your home. Acting as a miniature, self-contained ecosystem, a closed terrarium allows you to nurture tropical plants with minimal effort. Whether you’re a seasoned horticulturist or a curious beginner, this detailed guide will take you through everything you need to know: from selecting the right container and plants to step-by-step assembly, decorative inspiration, ongoing care, and troubleshooting common issues.
What is a Closed Terrarium?
A closed terrarium is a sealed glass vessel that creates its own water cycle, maintaining high humidity and stable conditions for moisture-loving plants. The transparent walls allow you to observe the dynamic growth and interaction among plants, soil, and water, forming a miniature landscape reminiscent of a tiny rainforest in your living room. The concept is simple yet magical: once watered and sealed, the ecosystem largely sustains itself, requiring only occasional intervention and indirect sunlight.
Essential Characteristics of a Closed Terrarium
- Self-sustaining water cycle: Water evaporates, condenses on the glass, and trickles back to the soil.
- High humidity: Perfect conditions for ferns, mosses, and other tropical plants.
- Low maintenance: Once properly assembled, ongoing care is minimal.
- Decorative glass container: Allows full view of layered soil, rocks, and thriving plants.
Gathering Materials: What You Need to Build Your Closed Terrarium
Before beginning the assembly, collect all necessary materials. Having everything on hand will ensure a smooth and enjoyable process. Use the checklist below to prepare:
- Glass container with lid (e.g., apothecary jar, large glass jar, bell jar)
- Plants suitable for high humidity (see recommended list below)
- Drainage layer materials (e.g., pebbles, gravel, small stones)
- Activated charcoal (to prevent odors and toxins)
- Fresh potting soil (preferably for tropicals)
- Moss (optional, for added green texture)
- Decorative stones, glass marbles, or shells (optional, for top dressing)
- Terrarium tools (e.g., long tweezers, chopsticks, spoon)
- Spray bottle (for watering and misting)
- Plastic tub or tray (to contain mess while planting)
Why Each Layer Matters
- Drainage Layer: Prevents waterlogging by creating a reservoir beneath the root zone.
- Activated Charcoal Layer: Filters impurities and prevents fungal growth; essential for long-lasting closed systems.
- Soil Layer: Provides nutrients and structure for root growth; depth varies according to plant size.
- Moss Layer: (optional) Retains humidity, covers soil, and adds aesthetic appeal.
- Decorative Top Layer: Stones, glass, or shells can be used to enhance the beauty and individuality of your terrarium.
Choosing the Right Container
The choice of glass container will influence your plant selection, the ease of access for planting, and the overall look of your terrarium. Selecting a container with a large opening makes assembly easier, while ornate jars lend elegance to the display. Ensure your jar can be tightly sealed with a lid to maintain the closed environment.
- Size: Larger containers allow for more ambitious plantings and creative landscapes.
- Shape: Wide openings simplify planting, while tall vessels highlight vertical plant growth.
- Material: Transparent glass is essentialâplastic is less ideal due to poor visibility and sealing.
- Lid type: Must seal well to lock in moisture; cork stoppers work but may not be fully airtight.
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Selecting Plants for Closed Terrariums
Not all plants will thrive in the unique, humid environment of a sealed terrarium. Choose plants that naturally grow in shaded, moist forest floors. Avoid succulents, cacti, or plants that prefer drier, brighter conditions.
Best Plants for Closed Terrariums
- Mosses: Sheet moss, mood moss, spike moss
- Tropical ferns: Maidenhair fern, button fern, asparagus fern
- Fittonia (nerve plant): Colorful leaf veining
- Pilea: Small-leaved varieties, e.g., Pilea depressa
- Peperomia: Dwarf ripple varieties
- Miniature orchids (for advanced terrarium keepers)
- Selaginella (club moss): Good for ground cover
Mixing plants of different leaf shapes and heights adds interest, but avoid overcrowding as plants will compete for space and light.
Plants to Avoid
- Succulents and cacti (require dry air)
- Herbs and vegetables (need more air circulation)
- Large houseplants
Step-by-Step Guide: Building a Closed Terrarium
- Prepare Your Vessel
Clean your container thoroughly to ensure no residual chemicals or oils could interfere with plant growth. Allow it to dry before beginning.
- Add the Drainage Layer
Pour in 1-2 inches of pebbles, stones, or gravel to create a drainage basin. This prevents water from saturating the soil and roots.
- Add Activated Charcoal
Sprinkle a thin layer (typically ½ inch) of activated charcoal over the pebbles. This keeps the terrarium environment fresh and odour-free by filtering toxins and excess moisture.
- Add a Sheet of Moss (Optional)
Lay a piece of sphagnum or sheet moss atop the charcoal to act as a barrier, preventing soil from filtering down into the drainage layer. This is optional but contributes to the longevity and tidiness of your terrarium.
- Add Potting Soil
Carefully add enough potting mix for your chosen plants (typically 2-4 inches, depending on plant size). Use a spoon or small scoop for greater control. Create subtle slopes or contours in the soil for visual interest.
- Arrange and Plant
Make holes in the soil with a chopstick, spoon handle, or your finger. Gently place each plant into its hole, cover roots, and press the soil gently around each plant. Use long tweezers for arranging plants in hard-to-reach areas, especially for tall, narrow jars.
- Add Decorative Top Layer (Optional)
Scatter stones, glass pebbles, or shells atop the soil for ornamentation. Add extra moss for a lush, green carpet effect. You might also add a small plastic or ceramic animal for whimsy.
- Water Sparingly
Lightly moisten the soil with a spray bottle or by gently pouring water at the edge of the container. Avoid oversaturatingâthe soil should be damp, not soggy.
- Seal Your Terrarium
Place the lid securely on your vessel. Your closed terrarium is now complete!
Tips for Arranging Your Terrarium
- Cluster smaller, low-growing plants at the front; taller species at the back.
- Create undulating terrain by varying soil height.
- Balance color, leaf shape, and plant size for visual diversity.
- Leave enough space for plants to grow; avoid overcrowding.
Closed Terrarium Ecosystem: How It Works
The sealed system of a closed terrarium mimics the natural water cycle on a miniature scale:
- Evaporation: Water in the soil and from leaf transpiration rises as vapor.
- Condensation: Moisture condenses on the cool sides and lid of the container.
- Precipitation: The condensed water droplets fall back onto the soil, restarting the cycle.
This closed loop reduces the need for frequent watering and stabilizes humidity, providing ideal conditions for tropical plants to thrive. Over time, the mini-ecosystem achieves a natural balance, supporting growth and decomposition.
Caring for Your Closed Terrarium
Although terrariums are low-maintenance, they do require some attention to ensure lasting health. With the proper care, a closed terrarium can thrive for yearsâsome have survived for decades!
Placement
- Light: Place in bright, indirect light. Direct sunlight can overheat the terrarium and scorch plants.
- Temperature: Keep in a stable environment, away from heating vents, radiators, or cold drafts.
Watering
- If the soil looks dry or no condensation appears for several days, lightly mist or add a small amount of water.
- If the walls are consistently dripping wet, remove the lid for a few hours to reduce humidity.
Pruning and Maintenance
- Trim yellow or dead leaves to avoid mold or rot.
- Prune plants as they grow to prevent overcrowding.
- Remove fallen debris or mold as needed.
- Clean the inside of glass with a soft, damp cloth if cloudiness impairs your view.
Fertilizing
- Rarely necessary. If plants seem weak, use a dilute, organic liquid fertilizer every 6-12 months, applied sparingly.
Common Problems and Solutions
| Issue | Cause | Solution |
|---|---|---|
| Condensation on glass | High humidity or overwatering | Ventilate by removing lid briefly |
| Mold or algae growth | Overwatering, poor ventilation, decaying material | Remove affected material, ventilate, reduce watering |
| Yellowing leaves | Too much water, inadequate light | Reduce watering, move to brighter spot (indirect light) |
| Wilting | Insufficient moisture, too little humidity | Lightly mist soil and foliage |
Decorative Ideas for Closed Terrariums
- Use colored stones or glass for unique visual accents.
- Add small figurines to create fantasy or woodland scenes.
- Arrange moss in patterns or geometric shapes.
- Experiment with miniature landscaping: create “hills”, “valleys,” or dry “riverbeds” using sand and rock.
Frequently Asked Questions (FAQs)
What plants are best for closed terrariums?
Mosses, small ferns, Fittonia, Pilea, and Selaginella are well-suited. Stick to plants that love humidity and low to medium light.
Should I use activated charcoal in my terrarium?
Yes. Activated charcoal absorbs odors and helps prevent the growth of mold or bacteria, keeping the environment clean.
How often do I need to water a closed terrarium?
Ideally, not often. Once cycles are established, a closed terrarium can go for months without additional water. Only add when the soil is dry and condensation is absent for several consecutive days.
Why is there condensation on the glass and is it a problem?
Condensation is normal during the day due to the cycle of evaporation and cooling. If the glass is constantly foggy or water pools, ventilate by removing the lid for a while and reduce watering next time.
Can I keep animals or insects in a closed terrarium?
No, it’s generally best to avoid introducing live animals or insectsâthey may not survive and could disrupt the delicate balance. Add only plastic or ceramic decorations for visual interest.
How long can a closed terrarium last?
With attentive care and occasional pruning, a closed terrarium can survive and thrive for yearsâsometimes decades.
Final Tips and Inspiration
- Research each plantâs light and moisture requirements before planting together.
- Embrace experimentation. Each terrarium is unique and evolves over time!
- Introduce your creation into living spaces as a natural, calming accent piece, or give as a thoughtful, eco-friendly gift.
With patience and creativity, you can craft an enchanting, ever-changing green world inside glassârequiring minimal care but offering continual delight. Try your hand at building one today and enjoy a touch of indoor wilderness, right at your fingertips.
References
- https://blog.mytastefulspace.com/2019/04/03/closed-terrarium-101-7-easy-steps-to-build-your-glass-terrarium/
- https://www.gardenia.net/guide/closed-terrarium-101-maintenance-plants-and-more
- https://www.naplesgarden.org/diy-closed-terrarium/
- https://www.instructables.com/The-Basics-of-Closed-Jar-Terrariums/
- https://www.gardenista.com/posts/gardening-101-how-to-make-a-closed-terrarium/
- https://www.youtube.com/watch?v=7Lg4tzkHgVo
- https://www.gardenista.com/tag/terrariums/
- https://www.youtube.com/watch?v=2UQprMch2-I
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