Mold on potting soil: 4 tips that will save houseplants…

Mold on potting soil is a common problem with houseplants. As the mold can spread to the plant and damage it, there is an urgent need for action. Some types of mold are also dangerous to your own health as they enter the respiratory tract via the air in the room.

The following tips explain how to recognize mouldy potting soil, which household remedies help and how to prevent it.

The best ideas for plants and garden design can be found here. (Scroll down for the article.)

Mould on potting soil: 4 tips to save houseplants

1. recognize mould

It doesn’t always have to be mold if a whitish coating forms on the potting soil. Under certain circumstances, it may simply be limescale deposits from the irrigation water. This remains when the water evaporates from the surface. Limescale residues can be recognized by the fact that they are hard and crumbly. They are merely an aesthetic problem and can simply be scraped off with a spoon.

If you have very hard tap water at home, you can prevent limescale residue by boiling the irrigation water beforehand and allowing it to cool down. If, on the other hand, the coating is soft and furry, it is mold. Simply scraping off the top layer of soil is not enough. The invisible mycelium of the mold reaches far down into the potting soil.

2. combating mold on potting soil with household remedies

If the potting soil is acutely infested with mold, the plant must be repotted immediately:

  • Place it outside so that the mold spores do not get into the indoor air.
  • Knock most, but not all, of the potting soil from the roots. You can dispose of the moldy soil in the compost or household waste, where it will do no harm.
  • Now clean the flower pot. Wash it out with methylated spirits or vinegar. Terracotta pots can also be placed in the oven at 200 °C for 20 minutes – this heat treatment kills all mold spores.
  • Place the plant in new soil. In the fall and winter, when the plants are not growing so much but are in a dormant phase, the roots can be cut back slightly with clean scissors before planting. This will prevent the mold from spreading to the plant.

3. take precautions against mold

Mold is caused by waterlogging or persistent moisture. The following tips and tricks prevent mold growth:

  • Before watering, feel whether the top layer of soil on the potted plant is really dry. If it is still damp, the plant does not need more water. As the water requirement of plants decreases in winter, too frequent watering during this time is the main reason for moldy potting soil.
  • Flower pots with a drainage hole and saucer are advisable. To prevent the soil from being washed away through the drainage hole, cover it with a coffee filter or a piece of cloth.
  • Plants that need little water are best watered via the saucer. The soil will then gradually absorb the water without getting too wet.
  • A drainage layer of expanded clay in the lower part of the pot is also helpful. A finger-width layer of expanded clay before filling the pot with potting soil is enough to ensure good drainage of excess water.
  • Make sure to repot flowers regularly. Once the soil is “silted up”, the irrigation water can no longer drain away properly and builds up on the surface. Low-quality potting soils are usually affected more quickly than high-quality potting soils.
  • Sprinkling bird sand on the potting soil promotes the evaporation of surface water. This also reduces the risk of mold growth.

4. measures that should be avoided

Sometimes you can read recommendations on the internet, but these are of little help against moldy potting soil or even endanger the plant:

  • Simply sprinkling bird sand on the mold does absolutely nothing. The mold will continue to grow under the layer of sand.
  • Be careful when tapping off the old potting soil so as not to damage the roots. There is no need to remove the soil completely. On the contrary: it makes potting up later more difficult.
  • Do not add fungicide or other household remedies against mold to the irrigation water. There is a risk that such agents will not only kill the mold, but also the plant.
  • We also advise against the idea of rubbing the roots with methylated spirits or vinegar. This is more harmful to the plants than any mycelium.

With these tips, your houseplants will be well armed against mold infestation in the future.