A well-maintained terrarium can thrive for years with minimal intervention. However, understanding the nuances of terrarium care—from watering schedules to recognising early warning signs—makes the difference between a flourishing miniature garden and a disappointing failure. This guide covers everything you need to keep your terrarium healthy.
Understanding Your Terrarium's Ecosystem
Before diving into maintenance routines, it's essential to understand how your terrarium functions as a self-contained ecosystem. In a closed terrarium, plants release moisture through transpiration, which condenses on the glass and drips back into the soil—creating a continuous water cycle. Open terrariums operate differently, with moisture escaping into the surrounding air, requiring more frequent intervention.
This fundamental difference means that maintenance approaches vary significantly between terrarium types. Treating a closed terrarium like an open one (or vice versa) is one of the most common reasons terrariums fail.
Watering: The Most Critical Skill
Proper watering is both the most important and most frequently misunderstood aspect of terrarium care. The enclosed nature of terrariums means that water has nowhere to evaporate, making overwatering far more dangerous than underwatering.
Watering Closed Terrariums
A properly established closed terrarium should need watering only a few times per year. The internal water cycle handles most moisture needs. However, you should monitor for these signs:
Signs Your Closed Terrarium Needs Water
- No condensation visible on the glass for several days
- Soil appears lighter in colour and dry to touch
- Plants appear wilted or leaves are curling inward
- Moss has lost its vibrant green colour and appears brown
When watering is needed, mist lightly rather than pouring water directly. Add small amounts—it's easier to add more water than to remove excess. After misting, observe over the next few days. Healthy condensation should appear within 24-48 hours.
Watering Open Terrariums
Open terrariums require more regular attention since moisture escapes into the air. For succulent terrariums, water every 10-14 days during warmer months and every 3-4 weeks in winter. The soak-and-dry method works best: water thoroughly until it drains into the gravel layer, then wait until the soil is completely dry before watering again.
Tropical plants in open terrariums need more frequent watering—typically weekly. Check the soil moisture by inserting a wooden skewer or your finger about two centimetres deep. If it feels dry, it's time to water.
Golden Rule
When in doubt, don't water. Underwatered plants can recover; overwatered plants often cannot. Wait an extra few days and observe before adding moisture.
Light Management
Light is the engine that powers your terrarium's ecosystem. Without adequate light, plants cannot photosynthesise, leading to weak growth, pale leaves, and eventual death. Too much direct light, however, can overheat enclosed containers and scorch delicate foliage.
The ideal placement provides bright, indirect light for most of the day. A north-facing window is often perfect in Australian homes, or an east-facing window that receives gentle morning sun. South and west-facing windows typically provide too much intense afternoon light, especially in summer.
Seasonal Light Adjustments
As seasons change, so does the quality and duration of natural light. During Australian winters, you may need to move your terrarium closer to windows or supplement with artificial lighting. In summer, you might need to move it further from windows to prevent overheating.
Watch for these warning signs of light problems:
- Too little light: Pale, stretched growth; plants leaning strongly toward light; slow growth
- Too much light: Bleached or brown patches on leaves; soil drying too quickly; excessive heat inside closed terrariums
Temperature and Humidity Control
Most terrarium plants thrive between 18-24°C—comfortable room temperature for most Australian homes. Avoid placing terrariums near heating vents, air conditioners, or in direct paths of drafts. These cause rapid temperature and humidity fluctuations that stress plants.
Closed terrariums naturally maintain high humidity, but if you notice your tropical terrarium struggling, lightly mist the interior. For open terrariums with humidity-loving plants, consider grouping them with other plants or placing a shallow water dish nearby to increase local humidity.
Pruning and Plant Management
Regular pruning keeps your terrarium looking attractive and prevents overcrowding. Plants in the humid, stable environment of a closed terrarium often grow faster than you might expect, and without pruning, they can quickly outgrow their space.
When to Prune
Prune when plants touch the glass walls or lid, when one plant begins to overshadow others, or when dead or yellowing leaves appear. For most terrariums, monthly inspection and light pruning is sufficient.
How to Prune
Use clean, sharp scissors or pruning snips. For narrow-necked containers, long tweezers or specialised terrarium tools make the job easier. Remove dead material promptly to prevent mould growth. When trimming healthy growth, cut just above a leaf node—this encourages bushier growth and prevents unsightly stubs.
Pruning Tips
- Always remove dead or dying material first
- Prune in small amounts; you can always cut more
- Clean tools with rubbing alcohol between plants to prevent disease spread
- Remove trimmings immediately to prevent rot
Cleaning and Glass Maintenance
Clean glass ensures maximum light transmission and lets you enjoy your miniature garden clearly. For exterior cleaning, use a damp cloth or glass cleaner, taking care not to let cleaning solutions drip inside.
Interior cleaning requires more delicacy. For closed terrariums, condensation usually keeps the glass relatively clean. If mineral deposits or algae develop, use a long cotton swab or soft brush dampened with plain water. Avoid harsh chemicals that could harm plants.
Troubleshooting Common Problems
Excessive Condensation
Some condensation in closed terrariums is normal and healthy. However, if you can't see through the glass or water pools at the bottom, there's too much moisture. Open the lid for a few hours to allow excess moisture to escape. Repeat daily until condensation returns to normal levels.
Mould and Fungus
Small amounts of white fuzzy mould are common in new terrariums and usually resolve on their own. If mould persists or spreads, improve air circulation by opening the lid more frequently. Remove heavily affected plant material. A light dusting of cinnamon (a natural antifungal) can help in persistent cases.
Pest Infestations
The enclosed environment makes terrariums resistant to many pests, but they're not immune. Fungus gnats are the most common issue, typically indicating overwatering. Allow soil to dry more between waterings and consider adding a thin layer of sand to discourage egg-laying.
Yellowing Leaves
Yellow leaves can indicate several issues: overwatering, underwatering, insufficient light, or natural ageing. Check soil moisture first, then evaluate light conditions. Some leaf yellowing is natural as plants shed older growth—remove these leaves to maintain appearance and prevent decay.
Seasonal Maintenance Calendar
Spring
Growth accelerates as days lengthen. This is an excellent time for more aggressive pruning and, if needed, replacing struggling plants. Increase watering frequency slightly for open terrariums.
Summer
Monitor for overheating, especially during heatwaves. Move terrariums away from windows if necessary. Check moisture levels more frequently in open terrariums.
Autumn
Growth slows as days shorten. Reduce watering frequency and prepare for winter by ensuring terrariums have adequate light access.
Winter
Minimal growth period. Water sparingly and avoid fertilising. Consider supplemental lighting if your space receives limited natural light.
Long-Term Success
A well-maintained terrarium can last for years—even decades. The key is consistent, gentle care rather than neglect followed by intensive intervention. Spend a few minutes each week observing your terrarium, addressing small issues before they become major problems.
Remember that terrariums are living systems that change over time. Some plants may outcompete others; new growth patterns will emerge. Embrace these changes as part of your terrarium's evolving story, and don't hesitate to make adjustments when needed.
For more specific guidance, explore our articles on common mistakes to avoid or dive deeper into lighting requirements.