What to Do if Mold is Growing on the Soil of Your Plants?

Do not be surprised if you wake up one morning and see your favorite plant with a layer of white mold on its soil during winter. Mold loves dampness, low-light, and warm temperatures, making the average winter house plant the perfect breeding ground! Is it harmful? Can you prevent it?

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Common Questions About Mold on Plant Soil

What kind of mold is it?

The layer of mold on your plant soil is likely harmless, saprophytic fungus. All soil contains mold spores. But your plant happens to be producing the right conditions for the spores to bloom, causing a white, fluffy layer.

Will it harm my plant?

The answer is: no. In itself, the saprophytic fungus will not damage your plant. However, it can be a clear warning sign to indicate that your plant is experiencing dangerous conditions. For instance, it may be staying too moist, lack the proper air circulation, or need more sunlight. Ignoring these indicators is detrimental to your plant's overall wellbeing.

How can I get the mold off my soil?

There are a few things to consider before answering this question.

• What season is it? If your plant is dormant, repotting is not a good option unless the mold on the soil is severe. However, in the growing season, repotting is a straightforward option. Remember, some plants, like the Hawaiian Palm, have "reverse" growing seasons, so they are dormant during the summer months and growing during the winter. Do your research before you decide!
  

• When was the last time I watered? If you opt to repot your plant, that means you are also rewatering. If your plant is staying too moist, repotting/rewatering at this point will overwater your plant, causing root rot, which is almost irreversible.

• How extensive is the mold? If there is an infestation that includes mold on the soil surface and on the plant itself, you must take extreme measures. Contrastingly, if you only have a thin layer on the soil, there are a few easy, noninvasive techniques.
  

• What are my plant's light and ventilation requirements? Ultraviolet rays from the sun kill mold. Placing your plant in the sunlight for a day will help eliminate the growing fungus. However, you must weigh this decision with the overall care of your plant. Additionally, placing your plant in a well-ventilated area can prohibit mold on the soil surface, as long as your plant isn't overly sensitive.

The Best Noninvasive Methods of Removing Mold

Temporarily Placing Your Plant in Direct Sunlight

Placing your plant in direct sunlight will eliminate the mold growing on the soil surface, even if it is just for a day or two. Consider making this a regular part of your watering routine if it suits your plant's care requirements, especially for the winter months. (For example, the Crispy Wave Fern quickly gets sunburnt, while the Tradescantia can withstand temporary bouts of direct light.)

Removing the Top Layer of Soil

Start by taking the proper precautions for your health by wearing a mask during the procedure. Secondly, take a spoon and remove the top 2 inches of soil. Thirdly, take a moist cloth and wipe down any mold residue that is on the plant stems. And, lastly, treat your plant with a natural fungicide. The easiest solution? Sprinkle a thin layer of cinnamon on the soil and plant stems.

Invasive Methods of Removing Mold

Repotting Your Plant

If you decide that the outbreak warrants repotting your plant, make sure you use fresh soil and a new pot.

If you plan on reusing your existing plastic or ceramic container, clean it carefully with water and bleach. If you have a terracotta clay pot, replace it with a new one.

Spray your plant's stems with a natural fungicide, such as neem oil (which you can buy pre-diluted or dilute yourself).

Remember, all dirt contains mold spores! In addition to repotting, you will also have to change the plant's location or your watering habits to prevent mold from regrowing on the soil in the future.

How can I prevent mold?

Chances are, you are experiencing this issue with the change of season. Plants do not require as much water when they are dormant, but it can be challenging to pinpoint when dormancy begins for each individual.

Mold on the soil is a clear indication that your plant needs less frequent watering and is likely dormant (if it is the appropriate season). After removing the mold using one of the above methods, allow your plant to dry out more between watering.

If possible, relocate your plant to a well-ventilated area, keeping in mind your plant's requirements. (For instance, Crispy Wave Ferns do not do well in drafty areas.) Remember to continue supplying your plant with plenty of humidity in its new space.

Reevaluate the amount of sun your plant is receiving. If the winter months have arrived, your plant will likely experience fewer daylight hours in its current location. If you have a Crispy Wave, search out a new area in your home with brighter indirect light and no drafts. For plants like the Tradescantia, try leaving it in a sunny location for a day or two after watering, and then place it back in its usual area.

Make sure to remove all dead or decaying matter from your plant: this includes anything that may have fallen on the topsoil and any dead leaves currently attached to the plant.

Tip: Make use of porous rocks by loosely scattering them on the topsoil of your plant. Sandstone, pumice, and river rocks will soak up dampness from the topsoil, preventing it from developing saprophytic fungus. These rocks will then release the moisture into the air, increasing humidity.

As your plant collection grows year after year, you will come to find that a little layer of mold on the soil surface is a common issue. If this is your first time experiencing it, we trust that you will now be well equipped to deal with the problem in the future!

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