What You Need: Supplies List
Before you start, gather these materials. Most items are inexpensive and easy to find at grocery stores, pharmacies, or online.
| Item | Purpose | Where to Find It | Estimated Cost |
|---|---|---|---|
| Live Physarum polycephalum culture or sclerotium | Your slime mold starter | Science suppliers, eBay, educational kits (full buying guide) | $5-15 |
| Petri dishes (9-12 cm) with lids | Growing container | Amazon, pharmacy, science supply stores | $5-10 for a pack of 10 |
| Plain oat flakes (uncooked) | Primary food source | Any grocery store | $2-4 |
| Non-nutritive agar powder (optional) | Gel substrate for growing | Amazon, Asian grocery stores, science suppliers | $5-10 |
| Paper towels or coffee filters | Alternative to agar substrate | Any grocery store | $1-3 |
| Spray bottle (fine mist) | Maintaining humidity | Dollar store, pharmacy | $1-3 |
| Distilled or filtered water | Misting and substrate preparation | Grocery store | $1-2 |
| Tweezers or toothpicks | Handling food and removing waste | Pharmacy, dollar store | $1-3 |
| Aluminum foil or dark cloth | Light protection | Any grocery store | $1-2 |
Agar vs. Paper Towel: Which Substrate?
Agar provides a cleaner, more professional setup where you can clearly see the plasmodium's network. Damp paper towels are simpler and work perfectly well for beginners. If this is your first time, start with paper towels. You can upgrade to agar later.
Step-by-Step Setup
Option A: Paper Towel Method (Easiest)
- Prepare the container. Fold a paper towel to fit inside the bottom of your Petri dish. Moisten it thoroughly with distilled water, then pour off any excess. The towel should be damp throughout but not sitting in a pool of water.
- Place the slime mold. If you have a live culture, use tweezers to transfer a small piece (about 1 cm square) onto the center of the damp paper towel. If you have a sclerotium (dried slime mold), place it on the towel and mist it lightly. See our guide on reviving a sclerotium for detailed instructions.
- Add food. Place 2-3 plain oat flakes about 2-3 cm from the slime mold. Do not place them directly against it.
- Close the lid. Put the Petri dish lid on, leaving it slightly ajar (about 2 mm gap) to allow air exchange while retaining moisture.
- Find a dark spot. Place the dish in a dark, room-temperature location (20-25 degrees Celsius is ideal). A closet, cupboard, or covered shelf works well.
Option B: Agar Method (Cleaner Results)
- Prepare agar. Mix 10 grams of plain agar powder with 500 ml of distilled water in a saucepan. Heat while stirring until the agar dissolves completely. Do not add nutrients; plain (non-nutritive) agar works best because it discourages mold contamination.
- Pour into dishes. Carefully pour the hot agar into Petri dishes, filling each about one-third full (3-5 mm deep). Let them cool with lids on until the agar solidifies completely (about 30-45 minutes).
- Place the slime mold. Transfer your live culture or sclerotium onto the center of the agar surface.
- Add food. Place 2-3 oat flakes a few centimeters from the slime mold.
- Close and store. Seal with the lid (slightly ajar) and place in a dark, room-temperature location.
What to Expect: The First 48 Hours
Patience is important during the first two days. Here is a realistic timeline:
| Time | What You Should See | What to Do |
|---|---|---|
| 0-6 hours | Nothing visible. The slime mold is adjusting. | Leave it alone. Resist the urge to open the lid. |
| 6-12 hours | Slight color change, possible thin veins extending. | Still leave it alone. |
| 12-24 hours | Visible yellow network growing toward the oat flakes. | Check moisture. Mist lightly if the substrate looks dry. |
| 24-48 hours | Plasmodium has reached the food and is visibly consuming it. | You can now begin regular care. |
If you started from a sclerotium, add 24-72 extra hours to this timeline. Rehydration takes time, and the organism needs to fully "wake up" before it begins active exploration.
Daily Care Routine
Once your slime mold is established and actively growing, follow this routine:
Every Day
- Check moisture. The substrate should always be damp but never waterlogged. If it looks dry, mist lightly with distilled water. If water is pooling, tilt the dish and absorb excess with a paper towel corner.
- Check for contamination. Look for green, black, or white fuzzy patches that are not your slime mold. These are common molds. If you spot any, see the troubleshooting section below.
Every 2-3 Days
- Remove old food. Use tweezers to carefully remove oat flakes that have been fully colonized (they will look brown and deflated). Old food attracts contaminants.
- Add fresh food. Place 2-4 new oat flakes a few centimeters ahead of the advancing edge of the plasmodium. This encourages exploration and growth. For more on feeding, see our complete feeding guide.
Weekly
- Transfer to a fresh dish. Once the slime mold has covered most of the substrate or contamination appears, it is time to move it. Cut or peel a section of the plasmodium (about 2 cm square) and transfer it to a fresh Petri dish with a new substrate. The slime mold will not mind being cut; it heals rapidly.
Common Mistakes and How to Avoid Them
| Mistake | What Happens | How to Fix It |
|---|---|---|
| Too much water | Plasmodium drowns, becomes pale and thin. Mold grows. | Tilt dish, absorb excess. Improve ventilation. |
| Too little water | Plasmodium dries out, turns into sclerotium (goes dormant). | Mist gently. If it has dried fully, follow the revival guide. |
| Too much food | Uneaten oat flakes rot and breed contaminant mold. | Remove old food promptly. Feed 2-4 flakes, not handfuls. |
| Direct sunlight or bright light | Slime mold retreats, slows down, or enters dormancy. | Move to a dark location. Brief checks with dim light are fine. |
| Temperature too cold (<15 C) | Growth slows dramatically; may enter dormancy. | Move to a warmer room (20-25 C ideal). |
| Temperature too hot (>30 C) | Stress, accelerated drying, possible death. | Move to a cooler location. Never place near radiators or in direct sun. |
| Sealed container (no air) | Carbon dioxide builds up, organism suffocates. | Always leave the lid slightly ajar or poke small ventilation holes. |
| Using tap water | Chlorine and minerals can harm the plasmodium. | Use distilled, filtered, or boiled-and-cooled water. |
Troubleshooting
"My slime mold is not moving."
Check these factors in order:
- Temperature: Is it between 19-25 degrees C? Cold slime mold is slow slime mold.
- Moisture: Is the substrate evenly damp? Not wet, not dry.
- Light: Is the container in darkness? Even indirect room light can slow exploration.
- Recovery time: If you just received or transferred it, give it at least 24 hours before worrying.
- Food distance: Are the oat flakes close enough (2-3 cm) for the slime mold to detect them?
"There is green/black/white fuzz growing in the dish."
This is contaminant mold (typically Penicillium, Aspergillus, or Trichoderma). It is the most common problem in slime mold culture. Here is what to do:
- If the contamination is small and far from your slime mold, carefully remove the affected area with a clean tool.
- Transfer a healthy section of the plasmodium to a completely fresh dish with a new substrate.
- Reduce moisture slightly; contaminant molds thrive in overly wet conditions.
- Remove old food more frequently; decomposing oat flakes are the primary entry point for contamination.
"My slime mold turned hard and crusty."
It has entered the sclerotium stage. This is not death. The organism detected unfavorable conditions (too dry, too cold, or no food) and went dormant. You can revive it by placing it on a fresh, moist substrate with food.
"The yellow color is fading."
A healthy Physarum plasmodium is bright yellow to orange. If the color fades to pale yellow or almost white, the organism is stressed. Common causes: too much water, not enough food, or temperature stress. Correct the environmental conditions, and the color should return within a day or two.
Going Further: Experiments for Beginners
Once you are comfortable with basic care, try these simple experiments:
- Food preference test: Place different foods (oat flake, rice grain, small piece of mushroom) at equal distances from the plasmodium and observe which one it reaches first.
- Simple maze: Build a small maze from cardboard or plastic on the agar surface, place food at the exit, and watch the slime mold find the shortest path.
- Light avoidance: Cover half the dish with foil and leave the other half exposed to dim light. Observe where the slime mold goes.
- Division and reunion: Cut the plasmodium into two pieces, place them in separate dishes for a day, then reunite them. Watch how they fuse back together.
A Living Pet That Does Not Need Walking
Slime mold is sometimes called a "pet" because it requires regular care and responds to its environment in visible, engaging ways. But unlike a hamster or a goldfish, it can be put into dormancy (sclerotium) whenever you need a break. Go on vacation, and when you return, simply wake it up again. No pet-sitter needed.
Ideal Environmental Conditions at a Glance
For the full breakdown of environmental factors, see our dedicated guide on slime mold environment. Here is a quick summary:
| Factor | Ideal Range | Acceptable Range |
|---|---|---|
| Temperature | 22-25 C | 18-28 C |
| Humidity | 80-90% inside the dish | 70-95% |
| Light | Complete darkness | Dim indirect light |
| Air circulation | Lid slightly ajar | Small ventilation holes |
| Water type | Distilled water | Filtered or boiled tap water |
Growing slime mold is one of the most accessible and rewarding science activities you can do at home. With just a few dollars in supplies and a bit of patience, you will have a living organism that solves mazes, makes decisions, and teaches you about intelligence without a brain.