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In the soil of potted and tub plants, mold fungi can be found from time to time, but also larger fungi such as cap or pillar fungi. Mold spores can be found in certain quantities in every potting soil. Together with soil organisms, they help to break down organic materials. However, if they spread excessively, this can have various causes, from gross mistakes in care to large differences in the quality of potting soil.

Mushrooms in the potting soil


Basically, every growing medium contains a visible but also an invisible fungal flora, with a visible one indicating that the substrate has been kept too moist for a long time. The fungus actually lives in the ground. What you see on earth is the fruiting body. Which type of fungus dominates depends on the components of the substrate and the respective culture or care.

That's it intensive watering the most common cause of brown, white, or yellow fungus infestation. Together with warm ambient temperatures and a particularly nutrient-rich soil, fungal infestation is encouraged. In addition, the quality of the potting soil an important role, because certain components of inferior substrates are essentially responsible for the development of fungi. If not, it can do that too Material of the planter promote the development of fungi. This applies in particular to plastic pots, which cannot release any moisture through their pot walls, so that moisture accumulates in the pot. Unglazed clay pots are less of a problem because their porous surface allows moisture to evaporate.

These fungi do not initially harm the plants themselves. However, in extreme cases they can form a water-repellent layer on the potting soil, so that hardly any water can penetrate or the substrate or roots can be aerated.

fight fungi


If the problem with fungi on the potting soil gets out of hand, you should fight them. The first step should be repotting in fresh substrate.

  • The best time is during the vegetation-free period in autumn
  • Plants are best repotted in the fresh air
  • Remove old soil from roots
  • Use a new pot or clean the old one thoroughly
  • Preferably use vinegar water or high-percentage ethyl alcohol for cleaning
  • If necessary, shorten the roots before planting
  • Place a drainage layer of coarse gravel in the pot
  • Excess water must be able to drain off easily
  • Fill the drainage layer with fresh potting soil
  • Insert plant and fill with substrate

tip: After repotting, you should make sure that the soil is kept only moderately moist in order not to wet the substrate again and encourage renewed fungal infestation. Of course, this also depends on the requirements of the respective plant.

Casting as required

In order to combat these fungi effectively, the watering behavior should be reconsidered. Moisture is the biggest problem when it comes to mushrooms, especially too much of it. The water requirement varies from plant to plant. Some species like it rather dry, others prefer a constantly moist substrate. Exactly these properties should be considered.

  • Fight fungi by letting the substrate dry and keeping it drier in the future
  • Fungal infestation then usually reduces by itself
  • Finding the right balance when pouring is relatively difficult
  • Plant type and current environmental conditions determine the water requirement
  • In a warm and dry environment, a lot of water evaporates
  • In cool and humid climates, evaporation is much less
  • Water requirements are highest during the growing season
  • Significantly lower, during the dormant period, plants evaporate less water
  • Water requirements also affected by the material of the pot

There is no uniform rule on how to water correctly and according to requirements. It is best to check the moisture in the soil every few days. Depending on the type of plant, the soil is allowed to dry only superficially or to a depth of two centimeters or up to two thirds before watering again. Excess irrigation water in coasters should be removed about 20 minutes after watering.

Use good quality potting soil

Most plant substrates have a high proportion of organic substances, e.g. compost, bark humus, peat and wood fibre, in varying compositions. They are entitled. However, they also promote fungal growth, especially in combination with prolonged moisture.

Potting soil with a high proportion of compost is particularly susceptible. Their post-rotting organic substances, with simultaneous heavy waterlogging, form an ideal breeding ground for mould. In addition, it is suspected that young peat or peat substitutes in potting soil are the main causes for the development of fungi. For the sake of the environment, you should generally avoid products containing peat.

Mushrooms prefer to grow in soil with a high humus content. Accordingly, inferior soil with a high proportion of organic substances is particularly at risk. Of course, moisture also plays an important role in both the air and the earth. A high-quality potting soil should contain mineral components such as lava or sand, which ensure good ventilation and structural stability and can thus prevent waterlogging. It should crumble in your hand and not muddy when you pour it.

tip: Even if the risk of excessive fungal growth is lower with a high-quality potting soil, which one should always use, improper care can still lead to an increased occurrence.

Make your own potting soil

  • Mix screened compost with coconut fibers
  • Compost should be older than a year
  • Coconut fibers swell in water
  • They are structurally stable, rot only slowly and have a fungicidal (fungicidal) effect.
  • Fibers promote aeration and soil storage capacity
  • For lower nutrient requirements, mix one part compost with four parts coconut fiber
  • Mixture in a ratio of 1:1 for higher nutrient requirements
  • Add some horn shavings as a source of nitrogen

Harmful to health, especially for allergy sufferers

People with a healthy immune system can easily cope with fungi that leave their spores on the small substrates of flower pots. However, fungi in the potting soil are less of a problem for the plants than for sensitive people such as allergy sufferers. The larger the pots, the higher the number of fungal spores. They get into the air we breathe, are inhaled and can both trigger allergies and, in the case of existing allergies, lead to health problems, especially of the respiratory tract. This makes it all the more important to regularly check your houseplants for fungal infestation and to act as quickly as possible if they are found.

prevent fungi

Fungi in potting soil cannot be completely prevented. Nevertheless, you can prevent them by watering moderately, ensuring good drainage and not leaving water in saucers. For those who travel a lot, there are special ones irrigation systems on. The compost in the soil should always be ripe, i.e. left to sit long enough, then it is less susceptible to fungal growth.

It is better to avoid particularly rich and dense soil or, if necessary, make it more permeable with a little sand. What should also be avoided are long storage times. They increase the salt content in the soil, which can lead to plant damage. In addition, the pH value can change and the structural stability can decrease. Finally, the location where the plant is located should always be well ventilated.

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