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Potting Soil Molds: Avoid These Mistakes to Prevent Mold on Potting Soil (+ Bonus Trick)

It’s annoying when your beloved houseplants suddenly get moldy plant soil. But fortunately, this problem is usually solved faster than some other plant problems (some pests, for example). Improper care is usually the reason why a plant has moldy soil, and if you adjust your routine accordingly, you can not only get rid of it, but also prevent a new infestation. We explain what mistakes you should avoid and also have a trick you can try against mold infestation on potting soil.

You keep the soil too moist for too long a time

Loosen soil or add drainage with gravel

It’s no secret that the combination of heat and humidity are the ideal conditions for mold to spread. So why does potting soil mold? Because the soil is too moist! And although there are some plant that can lower the humidity and thus prevent mold growth in the room, even these specimens are helpless if you keep the potting soil moist in the long run. So what can you do?

  • Reduce watering

In winter, plants have their resting phase and need less water than during their growth phase. However, care must be taken here so that the plants do not dry out in turn. So instead of watering less frequently, it’s better to simply reduce the amount of water you give. Give the soil enough time for the top layer of soil to dry out. That way, mold spores won’t have a chance to spread, and there’s no risk of the plant soil becoming moldy.

  • Water from the bottom

Potting soil keeps getting moldy because you can’t estimate the right amount of water?

Another way to keep the top layer of soil dry and thus not give mold an ideal breeding ground is to simply water the plant from below. That is, you simply pour the water into the drip tray and let the plant do the rest. It will soak up the necessary amount of water. Give it half an hour and water again if needed. The excess that remains after the elapsed time can be discarded or used for other houseplants. No water should be left in the drip tray, as this in turn will lead to waterlogging and root rot in the long run.

What you can do about mold in the flower pot, you will learn in this article .

Plant soil molds in the home, if the location is unfavorable.

Potting soil mold - causes, faults and how to solve the problem.

Too dark, too dry, too humid, too cool – all these are factors that can quickly lead to the fact that you are tempted to over-frequent watering, or that the potting soil can not dry quickly enough.

  • Bright, but not too dry should be the location.

If it is dark and cool, the potting soil may become moldy because it dries significantly slower. Therefore, find your plant a bright place! It does not have to be direct sunlight if your plant species does not tolerate it. In any case, the brightness ensures that the soil dries faster. It is also important to avoid the dry air of the heating system, so that you are not tempted to keep watering.

  • Avoid stuffy rooms

Yes, humidity also plays a role in how quickly potting soil dries, of course. To prevent your potting soil from becoming moldy, a healthy exchange of air is very important. This means that you should ventilate regularly. So a stuffy basement or bathroom without windows might not be a favorable location.

Plant soil molds – The potting soil is not permeable enough

Potting soil molds if watered incorrectly, in an unfavorable location, and if the soil is too firm

The loamier the soil, the more moisture it retains and, accordingly, the slower it dries out. Of course, this is very useful for many plants in the garden in the summer. In the cold winter, even indoors, this can in turn be a disadvantage, especially if you want to prevent the plant soil from becoming moldy.

  • Use loose potting soil

A looser consistency of the substrate means better air circulation, which is not only good for the plant itself (more oxygenation through the roots), but also results in more optimal drying. Mix your own substrate! For this purpose, you can simply mix the normal potting soil bark of pine trees, as well as clay granules. Coconut fibers, which are increasingly used even for orchids, are also suitable as an additive.

  • A good drainage

Alternatively, you can also add drainage. For this, simply add a thin layer of pebbles to the pot before the soil. This prevents water from accumulating in the lower part of the pot (which also happens despite drainage holes), but can drain away. Accumulating water soaks up the top layer of soil like a sponge, so it is permanently moist.

Note: White coating on potting soil does not necessarily mean mold, but can also be caused by minerals. You can read about how to tell the difference between the two here.

Bonus tip: Sterilize soil for houseplants.

Prevent mold on potting soil by sterilizing it in an oven or microwave oven


You can prevent mold on potting soil by using home remedies (see the links above for a few). A really useful one is to sterilize the soil in the oven (the microwave is also suitable for smaller amounts), through which you will kill not only mold spores, but also all other pests and germs at once. So, if you make this routine a habit, you can prevent not only mold on potting soil, but also another infestation. How exactly does it work?

  • For the oven: before you use the purchased soil, spread it on a baking sheet. Preheat the oven to 180 degrees and put the tray inside. Now let the plant soil rest for about 30 minutes at this heat. Afterwards, let it cool down well before you plant your plants.
  • For the microwave: put the desired amount in a container that is microwave safe. Heat the soil for about 10 minutes at 600 watts.

Your potting soil molds in the bag? Then the oven variety is also a good option to kill the spores present. Direct sunlight is also suitable (e.g. for summer), as the UV rays work against mold spores. Simply spread the soil on a foil thin, so that the rays really get everywhere.

Plant soil molds if there is insufficient air circulation