Why Do My Terrariums Keep Dying? Here’s What You Might Be Doing Wrong

I love terrariums. There’s something magical about creating a tiny, self-sustaining world inside glass. But if you’ve ever set up a terrarium only to watch it slowly decline, don’t worry—you’re not alone! Terrariums can be surprisingly tricky to get right, but once you understand the common pitfalls, they become much easier to maintain.

Over the years, I’ve seen people struggle with the same few problems, so if your little ecosystem keeps failing, chances are one of these is the culprit. Let’s dive in.

1. Too Much or Too Little Water

Watering is one of the biggest mistakes people make with terrariums.

Closed terrariums don’t need frequent watering. If you’re seeing constant condensation on the glass, it’s too wet—just open the lid for a few hours to let it dry out slightly. Ideally, you should see a light mist in the mornings and evenings, but not excessive droplets running down the sides.

Open terrariums dry out much faster, especially with succulents or air plants. If your plants are shrivelling, you’re probably not watering enough. A light misting or a tiny splash of water once a week is usually enough.

2. Using the Wrong Plants

Not all plants thrive in the same conditions, and this is a huge reason why terrariums fail.

Closed terrariums are humid environments, so they’re best suited for ferns, moss, fittonia, and tropical plants. If you’ve put succulents or cacti inside a closed jar, they’re almost guaranteed to rot.

Open terrariums are great for succulents, air plants, and other drought-loving species. These plants hate excess humidity, so keeping them in a closed system is a death sentence.

3. No Drainage = Root Rot

One of the most overlooked parts of a terrarium setup is the drainage layer. If there’s nowhere for excess water to go, the roots will rot.

A proper terrarium should have a layer of gravel or pebbles at the bottom, followed by a thin layer of activated charcoal (which helps with odours and bacteria), then your soil.

For tropical plants, use rich, well-draining soil.

For succulents and cacti, a sandy, fast-draining cactus mix is essential.

4. Not Enough or Too Much Light

Terrariums are often placed in the wrong lighting conditions.

Too much direct sunlight will turn a closed terrarium into a sauna, essentially cooking the plants inside. If you’ve ever noticed plants wilting or crisping up, this could be why.

Too little light means your plants will struggle, grow leggy, or even die off completely. The best spot is bright, indirect light—near a window but out of direct sun. If your home is dark, consider an LED grow light to help.

5. Lack of Airflow = Mould & Decay

If your closed terrarium is sealed for too long, it can become a breeding ground for mould and fungus.

Opening the lid occasionally allows fresh air to circulate and helps prevent stagnant air buildup.

If you spot white fuzz on the soil or plants, it’s usually mould. Remove any affected parts and wipe down the glass with a diluted vinegar or hydrogen peroxide solution.

6. Forgetting to Prune & Maintain

Terrariums are small spaces, and plants can quickly become overgrown, competing for light and resources.

Trim back any plants that start getting too tall or overshadowing the others.

If leaves start yellowing, remove them so the plant can focus on new growth.

7. Extreme Temperatures

Terrariums don’t like sudden temperature changes. If yours is near a radiator, air conditioning vent, or a cold draft, it might be struggling due to stress.

Keep your terrarium in a stable environment, away from extreme heat or cold.

Final Thoughts

Terrariums are beautiful, rewarding projects, but they do require some attention to thrive. If yours keeps dying, it’s usually a simple fix—just tweak your watering, check your plant choices, and make sure the setup is right. Once you’ve got the balance sorted, a well-made terrarium should be a joy to care for, not a constant struggle.

Got questions about terrariums? We’ve got a new range launching soon, plus plenty of helpful tips on the blog. Stay tuned!