If potting soil is moldy, the soil was not necessarily contaminated. Much more often, storage conditions, watering behavior, or the composition of the potting soil are the causes of mold in the flower pot.
Whether peat or peat substitute, fresh or old potting soil, long open or freshly opened sacks – every potting soil molds under certain conditions. But mold on the potting soil can damage plants, is unattractive, and can irritate the respiratory tract of sensitive people. That’s why we explain everything about the causes, prevention, and control of mold in flower pots below.
What does mold on potting soil look like?
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Mold on potting soil is soft and fluffy and first appears in small round colonies on the substrate. It often gives off a somewhat musty smell and under the surface white fungal threads, the so-called mycelium can be visible.
With far advanced fungal growth, even conspicuous fruiting bodies develop, with which the fungus produces further spores for reproduction. Lime or salt deposits on the potting soil or the clay granulate on the earth look different: These are rather dry, hard, and crumbly.
Such depositions occur also rather than laminar and not in small pulks. The deposits are caused by too calcareous water on the one hand, and water “from below”, i.e. via the trivet, on the other.
Is mold on potting soil harmful?
Mold is also no problem for adult plants in pots. Young plants, however, can be strongly inhibited in their development and die from mold, especially due to the competition for nutrients.
Why does potting soil go moldy?
Potting soil can become moldy when fungal spores find optimal conditions for germination on its surface. Fungal spores are actually present everywhere in our air, so in principle, mold can always occur.
But some factors favor or inhibit the development of mold:
- High humidity: This is promoted by wet, poorly ventilated potting soils. Cheaper soils of fine black peat or soils with too high a compost content are therefore more often affected. High-quality, structurally stable, and loose soils such as Plantura organic soils are far less susceptible to mold.
- Warm temperatures: Most molds feel particularly comfortable in damp heat and multiply more quickly.
Incorrect storage: Sometimes potting soil molds already in the package. This does not necessarily have anything to do with poor quality, but with the condensation that forms on the film. Then small, harmless mycelium nests can appear at the air holes of the foil.
- Organic substance: Any largely organic substrate can sooner or later be decomposed, collapse, and thus create optimal conditions for mold. This applies to compost as well as to bark humus, wood fiber, or peat.
- By the way: The age or the storage period of the potting soil does not really have anything to do with the formation of mold. Also, the mold spores do not necessarily have to come from the soil, since they are found everywhere in the air.
How can you prevent mold on potting soil?
Mold on potting soil can be prevented by storing open and closed bags of soil properly and by regularly repotting, especially indoor plants. It is also important to use high-quality, structurally stable, and loose substrates.
- Store your soils protected from the weather, dark and cool.
- Repot plants in tubs and pots regularly, at the latest when the old soil appears to have collapsed and is no longer loose.
- Use high-quality potting soils, which, thanks to wood fiber, perlite, and expanded clay, sink less quickly and remain loose.
How to get rid of mold on potting soil?
This can be done to get rid of mold on potting soil:
- Sufficient ventilation of living spaces – this helps against any kind of mold in the house.
- Allow your plants a bright place – this is where mold feels less comfortable.
- Let the surface of the soil dry out regularly. Drying can be accelerated by roughening it with a fork. Water more often from below over the coaster.
- Remove the moldy layer of soil and spread a layer of sand on the pot surface. This dries particularly quickly. This will stop further spreading.
If the infestation is already very strong, the entire soil must be replaced. Rinse the old substrate with lukewarm water from the roots and pot the plant in a new container with fresh, high-quality potting soil.
- For some plants, sand, perlite, or coconut fiber can also be mixed in. These include, for example, carnivores, cacti, and succulents.