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White Mould on Plant Soil: What Does it Mean?

White mould appears as white fuzz over the top of the soil and can sometimes indicate more serious problems.

Finding white mould on the soil of plants might be a worry if you don’t know what it means. It diminishes visual appeal and looks like a cause for concern.

Getting rid of it is easy, as are the steps to help prevent it in the future.

Key takeaways

  • White mould on plant soil is harmless to humans and plants
  • The presence of white mould is an indication of more serious problems
  • The mould can simply be removed, but it is important to treat the underlying causes
  • The underlying causes are excessive soil moisture, low light and plant detritus (decaying plant matter)

What does mould on soil look like?

White mould on soil appears as white fuzz over the top of the soil or as white speckles. Left unchecked, it can form larger white patches and even on the base of the stem.

It is typically found on the soil at the base of plants.

Why does mould grow on plant soil?

Mould spores are a part of the soil ecosystem. Spores lie dormant unless they have access to food, water and oxygen.

These allow spores to germinate, and resulting fungi to grow.

Fungi food

Most fungi are saprophytic which means they get their nutrients from decaying plant matter.

Leaves and twigs dropped by the plant are the source of food for spores and fungi.

High soil moisture

High soil moisture can be caused either by over-watering, poor drainage or both.

If soil is overly moist, plant matter on the soil decays more quickly giving the fungi more nutrients.

High humidity and poor air flow

Humidity is the amount of water in the air. When high, the evaporation of water from the liquid in the soil to gas in the air is slow.

This prevents the passage of water from the soil to the air and so the soil stays damp.

Soil composition

Most soils contain a mixture of clay, sand and organic matter. Soils with a lot of sand drain more quickly.

If you’ve been finding white mould, it may be because the aeration and drainage provided by the soil are inadequate.

Low light

Unlike plants, fungi can grow without any light. Low light, therefore, gives fungi an advantage over plants.

Contaminated soil

White mould can originate from potting soil which has not been stored correctly or for too long.

Soil needs to be sealed whilst stored, and only has a shelf life of a couple of years. Stored for too long, soil can lose its ability to release moisture.

Is mould on soil bad for plants?

root rot | Plant care
White mould can lead to root rot / Photo by Ninjatacoshell / Wikimedia / CC BY-SA 3.0

White mould isn’t harmful to plants. However, it is an indication of plant problems.

White mould can lead to more serious conditions such as root rot if left untreated. Mould can also compete with the plant for nutrients.

I have found mushrooms and fungi on the soil of my outdoor container plants, and it turned out to be a sign that the plant – or soil – needed attention.

It’s a good idea to keep an eye on plant soil, and use it as an indicator for plant health.

How to get rid of mould on your soil

Simply scrape white mould from the top of soil and dispose of it. After that, you will need to take steps to ensure the mould doesn’t grow back.

Leave the pot in a bright and well-ventilated area. Avoid watering, and let the soil dry out. You can check for moisture by pushing your finger 5cm into the soil.

If drainage is an issue, put some perlite or other rocky material at the bottom of the pot.

If the mould comes back after drying, the problem may be the soil itself. Pot the plant again using fresh, sterile potting soil.

Use a new pot, or wash the existing pot in 10% bleach before using it again.

How do you prevent white mould on soil?

White mould can be prevented by checking that potting soil has been adequately sealed. After that, make sure to deprive the mould of the conditions it needs to survive. 

Check how much water your plant actually needs, and adjust by season. Plants require less water in the winter and autumn when growth is slower. As a rule, only water houseplants when the soil is dry.

You can also add a preventative fungicide to the top of the soil. These can be natural ingredients or chemical fungicides available for this purpose.

FAQ

Does cinnamon prevent mould?

Researchers have recently explored the antifungal properties of cinnamon powder along with other natural ingredients. The results showed that cinnamon has the potential to inhibit common tomato plant fungal diseases. Some say that you can use cinnamon powder to prevent fungus in the soils of house plants. It does have antifungal properties, but whether it works for you depends on how well the other conditions are managed.

Should I remove mould from soil?

White mould should be removed as it can spread to other parts of the plant. It is more important, however, to change the conditions which caused the mould to develop to avoid bigger problems.

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James Bartlett

James is an agriculture and sustainability author with over ten years of experience. His specialties are in the management of pests and diseases through biological or chemical means, as well as plant nutrition. He has authored articles on topics including plant care and how to maintain biodiversity in gardens. He has previously worked in nurseries, and today strives to keep an urban garden alive, healthy and thriving.

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