My terrarium is dying: the diagnosis flowchart

When your terrarium is failing — multiple plants dying, moss browning, general decline — it’s hard to know where to start. This flowchart walks you through it systematically.

Before you start

Take a photo of your terrarium right now. You’ll want to compare to “after” if things improve. Also note:

• When did the decline start?
• What changed recently? (moved jar? added plant? changed water?)
• Is the decline sudden or gradual?

The flowchart

Step 1: Is there a smell?

YES (bad smell):

• Anaerobic decomposition in substrate
• Action: Open lid immediately, let air out for 24 hours. Consider rebuilding if smell persists or is very strong.

NO:

• Continue to Step 2

Step 2: Is there visible mold?

YES, fuzzy white/green/black growth:

• See our mold guide
• Action: Identify the type (mycelium vs mold), wipe visible mold, add springtails

NO:

• Continue to Step 3

Step 3: Is the substrate soggy or bone dry?

Soggy (water pools when you poke a finger):

• Overwatering
• Action: Open lid, let dry out 48 hours, add dry substrate if needed

Bone dry (substrate pulling from glass):

• Underwatering
• Action: Add distilled water slowly, monitor

Normal moisture:

• Continue to Step 4

Step 4: Is there condensation in closed jar?

Heavy fog that never clears:

• Too humid, poor air exchange
• Action: Air exchange more frequently

No condensation at all:

• Too dry (closed jar should have some fog)
• Action: Add water, check lid seal

Light fog that clears daily:

• Normal — continue to Step 5

Step 5: Is the light appropriate?

Direct sun hitting jar:

• Too much light
• Action: Move or filter light

Deep shade (no window nearby):

• Not enough light
• Action: Move closer to indirect light, or add grow light

Bright indirect:

• Continue to Step 6

Step 6: Are the plants right for the conditions?

Plants that need low humidity (succulents, herbs) in closed jar:

• Wrong plants for environment
• Action: Remove and replace with humidity-lovers, or open the jar

Plants that need high humidity (cacti, succulents) in open dry jar:

• Wrong plants for environment
• Action: Replace with plants suited to your conditions, or close the jar

Right plants for the build:

• Continue to Step 7

Step 7: Have you added anything recently?

New plant added within last 2 weeks:

• May have brought pests or disease
• Action: Inspect new plant closely. Remove if suspicious.

Changed watering schedule or source:

• May be water-related issue
• Action: Revert changes, use distilled water

Moved the jar:

• Light/humidity change may be shocking plants
• Action: Move back to original spot if possible

No recent changes:

• Continue to Step 8

Step 8: Are temperatures stable?

Next to heating vent, window AC, or drafty area:

• Temperature swings stress plants
• Action: Move to stable spot

Stable room temperature:

• Continue to Step 9

Step 9: Is the cleanup crew present?

No springtails in a closed terrarium:

• Mold risk, organic matter accumulating
• Action: Add springtails immediately

Springtails present and active:

• Continue to Step 10

Step 10: Is it old age?

Some terrariums decline after 2-3 years even with good care. Substrate compacts, nutrients deplete, plants outgrow the space.

If your build is 3+ years old:

• Consider a full rebuild with fresh substrate
• Save any healthy plants/cuttings

If you’ve worked through all steps

And still can’t figure it out:

1. Take 3-4 photos (whole jar, close-ups of any issues)
2. Write down: build date, plants, watering, light, recent changes
3. Post in the Discord with this info

We’ll diagnose together.

The nuclear option

Sometimes the answer is rebuild:

• Smell won’t go away
• Multiple plants dying simultaneously
• Visible bacterial growth (slimy)
• Anaerobic conditions (standing water in drainage)

Rebuilding is frustrating but better than losing everything. Save what you can, start fresh with what you learned.

Prevention

Most “my terrarium is dying” situations result from:

• Wrong plant choice
• Overwatering
• Incompatible conditions (light, humidity)
• No cleanup crew in closed builds

Avoid these from the start and most builds will thrive for years.