Pick the method by how long you will be away
Slime mold does not need a babysitter for a weekend, and it does not need the freezer for a long trip. Everything depends on how long you will be gone.
| Time away | Method | What to do |
|---|---|---|
| 2 to 3 days | Nothing special | Feed it the day before, moisten the substrate, close the lid. It will be fine on its own. |
| 4 to 10 days | Fridge | Put the closed dish in the vegetable drawer, at about 8 to 10 °C, with one or two fresh oat flakes. Growth almost stops. |
| More than 10 days | Sclerotium | Put it into dormancy on purpose. It is the only truly safe method beyond two weeks. |
| Several months | Dry sclerotium | Once the sclerotium is dry and brittle, keep it in a paper envelope, somewhere dark. |
What really happens in the fridge
The fridge is the most common method for a short absence, and the most misunderstood. Slime mold does not go dormant in the cold. It slows down.
Between 8 and 10 °C, its metabolism drops to a fraction of its normal pace. It barely moves and eats almost nothing, but it is still active and keeps slowly using up its reserves. That works perfectly for one to two weeks and becomes risky beyond that, because its reserves run out before it has had any trigger to form a sclerotium.
Three precautions are worth taking. Use the vegetable drawer, the least cold and most stable part of the fridge. Make sure one or two intact oat flakes are left, with no surplus that could go moldy. And bring it back gradually: a slime mold moved straight from 8 to 24 °C suffers a shock it can take days to recover from. An hour at room temperature before you feed it is enough.
Making a sclerotium, step by step
A sclerotium is the dormant form slime mold adopts on its own when food and water run short. You can trigger it deliberately. The secret is to let it dry slowly, in the dark, without food.
Three days before: stop feeding
The slime mold needs to finish the flakes already in the dish, otherwise they will go moldy while it dries.
Two days before: move it to clean paper
Transfer it onto a fresh paper towel or a piece of filter paper with no food residue left on it.
The day before: open the lid a crack
Let the humidity drop gradually. Slow drying gives a far sturdier sclerotium than sudden drying. Keep the dish in the dark throughout. Light on a hungry slime mold tends to make it fruit and release spores rather than form a sclerotium.
The day you leave: take the lid off
The slime mold pulls back, thickens and turns orange-brown within 24 to 48 hours.
Once it is dry: store it in paper
The sclerotium is hard and brittle. Keep it on its paper, inside a paper envelope, never in closed plastic, in the dark and at room temperature.
Mistakes that ruin a sclerotium
Drying it too fast. A slime mold suddenly left out in the open air has no time to reorganize and dies instead of forming a sclerotium. It is the most common mistake. No fan, no radiator, no direct sun.
Storing it in closed plastic. Leftover moisture gets trapped and the sclerotium goes moldy within weeks. Paper lets it breathe.
Drying it with food left in the dish. Leftover flakes turn into a breeding ground for mold during storage and contaminate everything.
Putting it in the freezer. Ice crystals destroy its internal structures. The fridge slows it down, the freezer kills it. You may come across freezing protocols online, but none of them comes with evidence that a home freezer preserves slime mold.
Keeping only one. After long storage, one sclerotium in two sometimes revives less well. Always make two or three, from different pieces.
Keep a backup
If you are attached to your slime mold, always keep a spare sclerotium somewhere else. If your active culture dies from mold or an accident, you just wake up the backup. Take a piece of about 1 cm² from a healthy slime mold, lay it on clean filter paper and turn it into a sclerotium with the same slow drying. Once it is hard, slip it into a small paper envelope and put it away in a drawer.
Asking someone to look after it
If you would rather not put it into dormancy, anyone can look after a slime mold. Add two or three oat flakes every two or three days, check that the substrate stays damp with a light spray if needed, and keep the dish somewhere dark at room temperature. The instructions fit on a sticky note.
Print the instructions before you leave
The table of how long you can be away and the day-by-day sclerotium routine are on the slime mold care cheat sheet, a single page to leave next to the dish.
School holidays
A classroom is a different problem. The break is long, nobody comes in, and the room can heat up in summer. The fridge is not a practical option, and leaving a closed dish in a classroom at 28 °C means losing it.
The only reliable answer is to make a sclerotium before every holiday. What looks like a chore becomes a lesson in its own right: watching a sclerotium form explains a resistant life stage better than any diagram, and waking it up after the break restarts observation without buying anything. Planning across a full term is covered in slime mold in the classroom.
Frequently asked questions
How do I keep my slime mold while I'm on vacation?
Up to three days, do nothing. Up to ten days, the fridge at about 8 to 10 °C. Beyond that, put it into a sclerotium on purpose.
Can I put slime mold in the freezer?
No. Ice crystals destroy its internal structures. The fridge slows its metabolism, freezing kills it.
How long does a sclerotium keep?
Several years if it was dried slowly and stored dry, in paper and in the dark. A badly dried sclerotium will not last a few months.
Does slime mold remember what it learned after dormancy?
At least in some cases, yes. In 2019, Audrey Dussutour's team showed that slime molds habituated to salt were still habituated after a month as sclerotia. The salt they had absorbed while learning was still inside the sclerotium, which may explain this memory.
Sources
- Boussard A., Delescluse J., Pérez-Escudero A., Dussutour A., Memory inception and preservation in slime moulds: the quest for a common mechanism, Philosophical Transactions of the Royal Society B 374 (2019).
- CNES, Élève ton blob teacher resources (2021), in French.