The decision between an open and closed terrarium is more than aesthetic—it fundamentally determines which plants you can grow, how much maintenance you'll perform, and ultimately whether your terrarium thrives or struggles. Understanding these two distinct approaches helps you make the right choice for your space and lifestyle.
Understanding the Fundamental Difference
At their core, open and closed terrariums create entirely different environments. A closed terrarium is a sealed ecosystem where water continuously cycles through evaporation, condensation, and absorption. An open terrarium allows air exchange with its surroundings, meaning moisture escapes and must be regularly replenished.
This seemingly simple distinction has profound implications for every aspect of terrarium care, from plant selection to watering schedules to placement options. Neither type is inherently better—they simply serve different purposes and suit different preferences.
Closed Terrariums: Self-Sustaining Ecosystems
Closed terrariums capture the imagination because they function as miniature worlds. Once properly established, they can survive for months or even years with minimal intervention. The sealed environment creates a stable microclimate with high humidity and consistent temperature.
How Closed Terrariums Work
Plants inside a closed terrarium release water vapour through transpiration. This moisture rises, condenses on the cooler glass surfaces, and drips back into the soil—completing a continuous water cycle. Simultaneously, plants perform photosynthesis during the day, converting carbon dioxide into oxygen, and respiration at night, converting oxygen back to carbon dioxide. This creates a balanced atmosphere that sustains plant life indefinitely.
The Science Behind It
A properly balanced closed terrarium mimics Earth's water cycle in miniature. The glass walls act like our atmosphere, trapping moisture and creating the greenhouse effect that maintains stable conditions.
Advantages of Closed Terrariums
- Minimal maintenance: Once balanced, they may only need attention a few times per year
- Humidity-loving plants: Perfect for tropical species that struggle in dry Australian homes
- Consistent environment: Plants aren't stressed by fluctuating conditions
- Educational value: Demonstrates ecological principles in action
- Forgiving of forgetfulness: Ideal if you travel frequently or have a busy lifestyle
Challenges of Closed Terrariums
- Initial balancing: Finding the right moisture level requires patience and observation
- Limited plant options: Only humidity-tolerant species thrive
- Overwatering risks: Excess moisture has nowhere to escape
- Mould susceptibility: The humid environment can encourage fungal growth
- Heat sensitivity: Can overheat quickly in direct sunlight
Best Plants for Closed Terrariums
Successful closed terrarium plants share common traits: they tolerate high humidity, thrive in indirect light, and stay relatively compact. Excellent choices include fittonia (nerve plant), various ferns such as maidenhair and button fern, peperomia varieties, selaginella (spike moss), and traditional moss species. These plants create lush, tropical-looking displays that benefit from the stable, moist environment.
Open Terrariums: Flexible and Forgiving
Open terrariums offer greater flexibility in plant selection and are generally easier for beginners to manage. The open design allows air circulation, prevents moisture buildup, and makes access for maintenance straightforward.
How Open Terrariums Work
Unlike their sealed counterparts, open terrariums don't create a self-sustaining water cycle. Moisture evaporates into the surrounding air, meaning you must regularly water your plants. This increased maintenance is offset by the greater control you have over growing conditions and the wider variety of plants you can cultivate.
Quick Comparison
- Open: Regular watering needed, wider plant selection, easy access
- Closed: Self-watering, limited to humidity-loving plants, hands-off approach
Advantages of Open Terrariums
- Broader plant selection: Succulents, cacti, air plants, and many more options
- Lower mould risk: Air circulation prevents fungal problems
- Easier correction: Overwatering issues can be addressed by simply letting soil dry
- Direct sunlight tolerance: Many open terrarium plants handle bright light
- Simpler setup: No need to balance a sealed ecosystem
Challenges of Open Terrariums
- Regular watering: Requires consistent attention to moisture levels
- Environmental sensitivity: Affected by room humidity and temperature changes
- Dust accumulation: Open containers collect dust on plants and soil
- Pest vulnerability: More exposed to household pests
Best Plants for Open Terrariums
Open terrariums excel with drought-tolerant species that prefer lower humidity. Succulents are the classic choice—echeveria, haworthia, sedums, and crassula varieties all thrive. Air plants (Tillandsia) work wonderfully and add unique architectural interest. Small cacti can work in sunny locations, and even some herbs like thyme can grow in open terrarium conditions.
Making Your Decision: Key Factors to Consider
Your Maintenance Style
Be honest about your attention span and schedule. If you travel frequently, work long hours, or simply tend to forget about plants, a closed terrarium's self-sustaining nature may suit you better. If you enjoy the routine of plant care and want to engage regularly with your terrarium, open designs offer that ongoing interaction.
Your Preferred Aesthetic
The visual appeal differs significantly between types. Closed terrariums create lush, jungle-like scenes with rich green foliage and visible condensation that adds atmosphere. Open terrariums offer cleaner, more minimalist aesthetics, especially with sculptural succulents or architectural air plants. Consider which style complements your home décor.
Your Home's Climate
Australian homes often have dry indoor air, especially with air conditioning or heating. This makes closed terrariums advantageous for humidity-loving plants that would otherwise struggle. However, if you prefer succulents and other drought-tolerant species, the dry conditions actually work in your favour with open designs.
Available Light
Closed terrariums must be kept out of direct sunlight to prevent overheating, so they need spots with bright but indirect light. Open terrariums offer more flexibility—many succulent species actually prefer several hours of direct sun. Assess your available locations before deciding.
Decision Guide
Choose closed if: you want minimal maintenance, love tropical plants, and have indirect light available. Choose open if: you prefer succulents, want easy access for care, or have bright sunny spots.
Hybrid Approaches
Some terrariums blur the line between open and closed. Containers with small openings or loose-fitting lids create semi-closed environments with some air exchange. These can work well for plants that need moderate humidity without the full tropical conditions of a sealed terrarium.
Wardian cases—the Victorian-era predecessors to modern terrariums—often feature hinged lids that can be opened for maintenance and closed to maintain humidity. This flexibility allows you to adjust conditions as needed while still benefiting from the enclosed environment.
Starting Your First Terrarium
For absolute beginners, we often recommend starting with an open succulent terrarium. The forgiving nature of succulents, combined with the easier maintenance of open designs, creates a lower-stakes learning experience. Once you've developed confidence with watering schedules and light requirements, you can explore the more nuanced world of closed terrariums.
However, if tropical plants truly capture your imagination, don't let this advice hold you back. A closed terrarium with hardy species like pothos or fittonia can be equally forgiving, and the self-sustaining nature means fewer opportunities to make watering mistakes.
Can You Convert Between Types?
Converting an existing terrarium from open to closed (or vice versa) is possible but requires careful plant selection. You cannot simply seal a succulent terrarium—the plants will quickly rot in the humid conditions. Similarly, removing the lid from a tropical terrarium exposes humidity-loving plants to dry air they cannot tolerate.
If you want to change types, you'll need to start fresh with appropriate plants for the new environment. Consider it an opportunity to create something new rather than modifying what you have.
Making Your Choice
Both open and closed terrariums offer unique rewards. The lush, self-contained world of a sealed terrarium fascinates with its ecological elegance. The architectural beauty of succulents in an open container brings desert aesthetics indoors. Your choice should reflect your lifestyle, aesthetic preferences, and the conditions your home can provide.
Ready to begin? Explore our complete plant selection guide or learn about building your first terrarium.