There’s nothing quite as satisfying as watching a closed terrarium thrive on its own—a tiny ecosystem flourishing in a jar. But let’s be real: sometimes, things don’t go as planned. Plants wither, mold appears, and suddenly your terrarium feels less like a lush rainforest and more like a science experiment gone wrong.
If you’ve been there, you’re not alone. Many first-timers (and even seasoned DIYers) run into the same issues. The good news? Most of these problems are completely avoidable or fixable. Let’s dig into why closed terrariums fail and what you can do to keep yours healthy and happy.
1. The Drainage Layer Is Missing or Incorrect
A solid drainage layer is like the foundation of a house—it’s not glamorous, but it’s critical. Without it, water has nowhere to go, and your plants will end up sitting in a soggy mess. Root rot, mold, and dead plants are all common results of poor drainage.
How to Fix It:
Build a proper drainage layer with pebbles, activated charcoal, and mesh to separate the soil from the base. If you skipped this step or got it wrong the first time, check out How to Set Up the Perfect Drainage Layer for Your Closed Terrarium for a step-by-step guide.
2. You’re Overwatering (Oops)
It’s tempting to overwater your terrarium because, well, plants need water, right? But here’s the thing: closed terrariums recycle their own moisture. Too much water leads to mold, excessive condensation, and—you guessed it—rotting plants.
How to Fix It:
Water sparingly! You only need enough water to moisten the soil during setup. After that, look for condensation on the glass. If there’s too much water pooling at the bottom, you might need to carefully absorb some with a paper towel.
3. Wrong Plants, Wrong Place
Not every plant is cut out for life in a closed terrarium. Humidity-loving plants thrive in these conditions, but succulents and cacti? Not so much. They’ll rot faster than you can say “bad plant choice.”
How to Fix It:
Stick to terrarium-friendly plants like ferns, moss, and fittonia. These green buddies love humidity and low light, making them perfect for a closed environment.
4. You Forgot to Ventilate During Setup
This might seem counterintuitive for something designed to be sealed, but skipping ventilation during the setup process is a rookie mistake. Trapped moisture and lack of airflow create the perfect breeding ground for mold.
How to Fix It:
Leave the lid off for a few hours after setting up your terrarium to allow some airflow. Once things settle, seal it up and let the magic happen.
5. Overcrowding Your Terrarium
More plants, more problems. It’s easy to go overboard and pack your terrarium to the brim. But overcrowding leads to limited resources, poor airflow, and plants fighting for space like it's a botanical version of "Survivor."
How to Fix It:
Keep things simple. Use fewer plants and leave space for them to grow. A well-designed terrarium is about balance—not cramming every inch with greenery.
6. Neglecting Maintenance
Yes, closed terrariums are low-maintenance, but that doesn’t mean you can completely ignore them. Dusty glass, decaying leaves, and unwanted mold can turn your beautiful terrarium into a not-so-pretty mess.
How to Fix It:
- Clean the glass when it gets dusty.
- Remove dead or decaying leaves to keep things fresh.
- Spot any mold? Scrape it off and check for excessive moisture inside.
7. You Didn’t Use the Right Substrate
The substrate (or soil layer) supports your plants’ roots and holds nutrients. Using cheap potting soil or skipping substrate layers can create drainage and compaction issues.
How to Fix It:
Use high-quality, terrarium-friendly substrate. Many DIY terrarium kits come with pre-selected layers designed for this purpose, making it easier to get things right.
8. Lighting Problems
Finding the sweet spot for lighting can be tricky. Too much direct sunlight? Your plants could fry. Too little light? Your plants could wither.
How to Fix It:
Place your terrarium in bright, indirect light. A north- or east-facing window is ideal. Direct sunlight can cause overheating, so avoid putting it where the sun blazes in.
9. Ignoring Red Flags
Plants rarely just “die out of nowhere.” Yellowing leaves, moldy patches, or a funky smell are all red flags telling you something’s off.
How to Fix It:
Pay attention to your terrarium! A quick weekly checkup can help you catch and fix issues before they become big problems.
10. Rushing the Setup Process
Building a closed terrarium isn’t a race. Skipping steps, choosing the wrong materials, or rushing through setup can lead to problems down the line.
How to Fix It:
Take your time. Do your research. Read up on what not to do by checking out Common Mistakes to Avoid When Building Your DIY Closed Terrarium.
FAQ
Q: How often should I water my closed terrarium?
A: Not often! After the initial setup, monitor condensation levels. If you see moisture on the glass, your terrarium doesn’t need more water.
Q: Can I use any plants in a closed terrarium?
A: Nope. Stick to plants like ferns, mosses, and fittonia that thrive in high humidity. Avoid succulents—they prefer dry conditions.
Q: Why is there mold in my terrarium?
A: Mold is usually caused by too much moisture, poor ventilation during setup, or decaying organic matter. Remove the mold, reduce the humidity, and ensure proper airflow during setup.
Q: Can I put my terrarium in direct sunlight?
A: Avoid direct sunlight—it can overheat your terrarium and harm the plants. Bright, indirect light works best.
Q: Is a drainage layer really necessary?
A: Absolutely! A drainage layer prevents water from pooling at the bottom, which can lead to root rot. If you’re unsure how to set one up, check out this guide.
With a little care and attention to detail, your closed terrarium can thrive as a beautiful, self-sustaining miniature ecosystem. Happy terrarium-building!
