Guide
Mould in a terrarium
White mould blooms on fresh organics and leaves; springtails eat it. Most new jars fuzz white in their first weeks, and it fades on its own. The one to worry about is grey mould on weak plants.
- New jars usually fuzz white in the first weeks.
- Fallen leaves and leafy or bark top dressings keep feeding it, and it creeps to the ground beside.
- White mould is harmless to plants.
- Springtails graze it down; without them it can cover a fifth of the floor.
- Grey mould is a disease of weak plants in still, damp, dim jars.
- Growth
- 45% a day at full food
- Grazed
- 25% a day per 1,000 springtails
- Most cover
- 60% of a spot
The moulds and films a jar can grow
- Algae / cyanobacteria film on glass: A green film on the glass where light hits a wet jar.
- Blue-green mould: Blue-green powder on food scraps and fruit.
- Damping-off / root rot water mould: A water mould in soggy soil that rots roots and seedlings.
- Green mould: White fuzz that turns green on wood and soil.
- Grey mould: Grey fuzz on dying leaves and soft stems.
- Pin mould / bread mould: Fast grey fuzz topped with pinheads, on fresh organic matter.
- Slime mould: A bright yellow net or foam that creeps over wood and vanishes.
- Sooty mould: Black film on leaves where sap-sucking insects have been.
- White fuzzy mycelium (new-wood bloom): White fuzz on new wood and soil in the first weeks.
- Yellow houseplant mushroom: A little yellow mushroom that pops up from potting soil.
Keeping it down
- Add springtails before or right after sealing.
- Pick dead leaves out; they keep feeding it.
- Fogged glass all day means too wet: open the lid for a few hours.
- Give weak plants more light rather than more water.
See how springtails and isopods compare in springtails vs isopods.
More terrarium guides
- Closed vs open terrariumWhich to build, and which plants suit each.
- Best plants for a closed terrariumPlants that live sealed, easiest first.
- Best moss for a terrariumMosses for closed and open jars, and what they grow on.
- Terrarium layers explainedDrainage, barrier, soil and top dressing, and what each does.
- Terrarium drainage: LECA vs gravel vs lava rockEvery drainage material side by side.
- Springtails vs isopodsThe cleanup crew compared: what each eats and where it lives.