When mold appears on the potting soil, many people react almost in panic – rightly so, mold in visible proportions is neither healthy nor visually acceptable. This is what you can do against the unwanted covering, preventively and in the case of a current infestation.

Why does potting soil go moldy?

Mold spores are present in every soil to some extent. They are contained in every dead plant part, but also in humid air, you can’t really escape them completely. These spores are just waiting to spread, and it may just be a little too humid and/or a little too warm for that to happen. The mold already has ideal growth conditions. Then it depends on how many and which mold spores are waiting to start in a soil. First of all, you should check whether you are using the right potting soil.

The right soil for your plants

Have you ever thought about the fact that soil and potting soil are not the same? If your potting soil often gets moldy, you should definitely do it once. Because what you buy in the trade as “potting soil” often has very little to do with soil. Instead, you buy a mixture of all sorts of substances that are suitable for giving a potted plant support, storing and releasing water and fertilizer and can be moistened again even after it has dried out completely.

This can be compost or sand, but also wood chips and wood fibers, which actually have no place in soil, and a variety of other organic and mineral substances. And still a lot of peat is mixed in potting soil. An irreparable environmental outrage and a good chance of mold in the potting soil. Potting soil with a high proportion of old, ripe peat tends to mold because this peat structures the substrate far too finely. But even if young peat is used or if it is a peat-free product, you have a good chance of buying your mold with the potting soil.

If you have bought good potting soil that does not mold in the past and now want to buy it again and again, unfortunately you are not on the safe side either. The packs don’t necessarily contain the same soil every year. Every year, a new tender is made for the subcontracting, in which the cheapest supplier is usually awarded the contract.

Mold free soil

  • Get garden soil or topsoil and mix it with a third of mature compost
  • You can adjust the nutrient content yourself, with organic nitrogen (horn shavings) and trace elements (primeval rock flour)
  • if you want to loosen the soil for your plants, you should use peat substitutes that are coarser
  • e.g. B. coconut humus, stores water and air and is free of mold spores
  • Coconut humus is naturally slightly fungicidal and can often help to eliminate mold problems

Especially if you need a potting soil that is as low in nutrients as possible, you can also add perlite, a sterile substance with a rock structure that cannot become mouldy.

Prevent mold on the potting soil

Mold often develops when you try to water your plants preventatively, e.g. B. start a short vacation over the weekend. In this case, you can prevent mold growth by using an irrigation system. This will gradually provide the plants with water instead of watering the saucer full of water. As a result, an extremely mold-friendly climate is created very quickly, especially in warm temperatures. If you haven’t found a suitable watering system yet, it’s better to ask a neighbor to water your plants.

Mold growth can also be caused by the fact that you generally mean too well with the water supply to your plants. If the soil in the flowerpots is really wet for a while, mold tends to form on the soil. This time need not be very long, if there are many spores in the soil visible mold can develop from one day to the next.

By the way, your plants will also benefit from a well-dosed watering: Too much water is harmful for the plants. Experts estimate that overwatering causes more plants to die than any other maintenance mistake. Until you have drowned your plants by overwatering, you still have a good chance of attracting fungus gnats, which love moist potting soil and lay their larvae here.

If mold keeps appearing on the ground, high humidity and temperature may also be involved. But the first thing you should definitely do is review your watering habits.

Proper watering protects against mold

These tips will help you water your plants adequately, but not excessively:

  • Watering over water in the saucer is not in itself the worst method, especially if you are unsure of the amount of water a plant needs
    • control this irrigation
    • after about half an hour, discard any water that has not been consumed
  • pour from above, (with a few exceptions) only add water when the top layer feels dry
  • Forget the plant, don’t try to catch up on the forgotten watering with several generous waterings
    • immerse the plant completely in water until no more air bubbles come up
    • then drain very well
    • only water sparingly again when the soil surface is really dry
  • Some bird sand on the potting soil should also serve as a mold prevention measure, in which the spores cannot develop

Fight existing mold

If it has, you should remove mold from potting soil as soon as you notice it. Here is how mold removal should be done:

  • Carry plants outside and lay out foil that will later end up in the garbage
  • Remove plants from their pots
  • old potting soil is riddled with mold spores, it must no longer be used
  • Shake off as much soil as possible from the roots
  • Put plants with the “bare” roots possible in a washable plastic container
  • Rinse plant roots with water directly over a drain
  • Thoroughly clean plant pots with water that is as hot as possible, detergent and then a vinegar solution
  • Then fill the pots with fresh, mold-free potting soil and insert the rinsed plants
  • Fold the foil together with the old soil and place in a sealable garbage can

If you find this description quite “fussy” – when removing mold you should work really cleanly and thoroughly, because mold is by no means just an “optical disruptive factor”. This mold is also not completely harmless for us humans. In addition, a mold infestation can significantly promote the development of diseases in plants because it weakens the plant as a whole.

If mold has developed in the terrarium, you should first collect all fallen plant parts. However, the mold could also be introduced through the food of terrarium animals, here only regular cleaning of the bowls and their surroundings helps. Before you completely clear out the terrarium, you could try watering it with Lapacho tea for a while. This tree tea contains a substance that does not harm animals, but is used to make fungicides. Certain exotic species of isopods and springtails, which can be bought in pet shops, are said to be a magic cure for mold in the terrarium.

If you are cultivating plants that want to be kept in such heat and humidity that mold also thrives, it is better to keep these plants in a (small) greenhouse than to constantly expose a room in your apartment to high humidity and expose to temperature. The soil for such a greenhouse could then be made as mold-free as possible by heating it (120 degrees, at least one hour). You should also mix in some coconut humus. If there is very slight mold, you can try to kill the mold spores with Lapacho tea or Chinosol (pharmacy: as tablets to dissolve) in the irrigation water before you completely remove it.

When your potting soil gets moldy, it’s annoying, but it can be fought. If the measures mentioned here do not help, it may be helpful and necessary for you to find out about correct ventilation and appropriate humidity in living spaces. Or maybe you just need to change where you buy your potting soil.

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