Potting soil molds: causes, prevention & Control

If potting soil goes moldy, the soil was not necessarily contaminated. Much more often the storage conditions, the watering behavior or the composition of the potting soil are the causes of mold in the flower pot.

It doesn't matter whether it's peat or a peat substitute, fresh or old potting soil, a bag that has been open for a long time or a freshly opened bag - all potting soil molds under certain conditions. But mold on the potting soil can damage plants, is unsightly and can irritate the respiratory tract in sensitive people. That's why we explain everything about the causes, prevention and treatment of mold in flower pots below.

What does mold look like on potting soil?

Mould on potting soil is soft and fluffy and first appears in small round colonies on the substrate. It often gives off a slightly musty odor and white threads of fungus, called mycelium, may be visible beneath the surface. When the fungus growth is well advanced, conspicuous fruiting bodies are formed, with which the fungus produces more spores for reproduction.
Lime or s alt deposits on the potting soil or the clay granules on the soil look different: These are rather dry, hard and crumbly. Such deposits also tend to occur over a large area and not in small clusters. The causes of the deposits are too calcareous irrigation water on the one hand, and watering "from below", i.e. over the trivet, on the other.

Tip: If you want to get rid of unsightly limescale and s alt deposits, it is better to pour soft rainwater and at least occasionally from above onto the root ball.

Is mold on potting soil harmful?

Mould on potting soil is not dangerous for people with a he althy immune system. However, people with weak he alth or those allergic to mold should never inhale the spores and only work on infested pots with a face mask. Mold is also not a problem for fully grown plants in the pots. However, young plants can be severely inhibited in their development by mold and die, especially due to the competition for nutrients.

Why does potting soil go mouldy?

Potting soil can go moldy if fungal spores find optimal conditions for germinating on its surface. Fungal spores are actually present everywhere in our air, so mold can always occur. However, some factors favor or inhibit the development of moulds:

• High humidity: This is promoted by wet, poorly aerated potting soil. Cheaper soils made from fine black peat or soils with a high proportion of compost are therefore more frequently affected. High-quality, structurally stable and loose soils such as Plantura organic soils are far less susceptible to mould.
• Warm temperatures: Most molds thrive in humid heat and multiply faster.
• Incorrect storage: Potting soil sometimes gets moldy in the pack. This does not necessarily have anything to do with poor quality, but with the condensation that forms on the film. Small, harmless mycelium nests can then appear at the air holes in the film.
• Organic Matter: Any mostly organic substrate will sooner or later decompose and collapse, creating optimal conditions for mould. This applies to compost as well as to bark humus, wood fiber or peat.

By the way: the age or the storage time of the potting soil has nothing to do with the formation of mould. Also, the mold spores don't necessarily have to come from the earth, as they're found everywhere in the air.

Tip: However, if a large part of an unopened sack is streaked with mushroom mycelium, this is definitely a reason for a complaint. Because in this case the earth was obviously produced under bad conditions by the manufacturer or stored incorrectly by the dealer.

How to prevent mold on potting soil?

You can prevent mold on potting soil by storing open and closed bags of soil correctly and regularly repotting indoor plants in particular. 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 sagged and is no longer loose.
• Use high-quality potting soil, such as our Plantura organic potting soil, which sags less quickly and remains loose thanks to wood fibre, perlite and expanded clay.

Tip: You should only use heavily moldy potting soil in the garden and not in the house.

Fighting mold on potting soil

You can do this to combat mold on potting soil:

1. Adequate ventilation of living spaces - this helps against all types of mold in the house.
2. Give your plants a bright spot - mold doesn't feel as comfortable here.
3. Periodically allow the surface of the soil to dry out. Drying can be speeded up by roughening them up with a fork. Pour over the coaster from below more often.
4. Remove the moldy layer of soil and spread a layer of sand over the top of the pot. This dries particularly quickly. This stops further spread.
5. If the infestation is already very severe, the entire soil must be replaced. Rinse the old substrate out of the roots with lukewarm water and pot the plant in a new container with fresh, high-quality potting soil, for example our loose Plantura organic soil.
6. Sand, perlite or coconut fiber can also be mixed in with some plants. These include, for example, carnivores, cacti and succulents.

Tip: Home remedies to combat mold in potting soil: Vinegar, washing-up liquid, s alt, mold-fighting cleaning agents or similar are not an option if potting soil is moldy. You could change the soil chemistry and damage the plant. However, possible home remedies are pouring chamomile tea or sprinkling the surface of the pot with cinnamon powder. Both have a certain effect, but will only bring temporary relief if nothing else is done to combat the mold in the flower pot.

By the way: Cinnamon not only helps against mold on potting soil. Cinnamon in the garden is a versatile home remedy that can also be used against ants and animal pests, for example.

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