White mold is one of the most common plant problems for container gardens. Found on the soil of your plants, white mold can appear as either crusty or fluffy. White mold can also form in outdoor gardens. The air circulation and sunlight of the outdoors generally keeps white mold at bay, but consistently wet weather can cause the same problems outdoors as indoors. Containers, especially plastic containers, hold in moisture and so it can be extremely easy to overwater your plants. White mold thrives in moist conditions and can be dangerous for your plants and for you. Although not as dangerous to human health as black mold, white mold can still cause allergic reactions and symptoms similar to hay fever.

What is White Mold? How to Identify

White mold on the soil is a kind of saprophytic fungus. It is not just one species and may present itself in a variety of ways. A saprophytic fungus eats dead plant matter in the soil, but generally does not harm the plant itself. It is a normal part of plant soil and beneficial for breaking down plant matter into nutrients that the plant needs. In this way, white mold is a sign of healthy soil. However, it is also a sign of an imbalance in your plant’s needs. White mold grows in conditions that are too wet and dark, the opposite of what most plants need. When you find white mold, you should take steps to eliminate it.

Mold can easily set in on any surface. This is especially true if there are already spores floating around in the air from other infected plants.  White mold spores are microscopic and impossible to see with the naked eye. You won’t know they’re there until the spores take root and begin to spread.  White mold is easily identified by its fluffy, powdery appearance on wet soil.  Despite its name, white mold may not always appear white.  When the mold releases spores, it may appear to change colors to green or brown depending on the kind of white mold it is and what color its spores are.

Is White Mold Dangerous?

White mold isn’t particularly dangerous to plants, but it can lead to possible future problems. It is an indicator that your soil is too wet. Too wet soil may lead to root rot or stem rot which will kill your plants.

For humans, white mold is a minor irritant that may affect some individuals more than others. This is especially true if concentrations are high. The United States Environmental Protection Agency (EPA) recognizes molds as having potential to cause health problems in people. As such, it’s generally a good idea to treat mold whenever and wherever you find it.

Treating White Mold

So, how do you get rid of white mold on the soil from your in-ground or container garden? There are several options. As always, I prefer natural methods rather than harsh chemicals that are harmful to the environment and your plants.

Prevention

The old adage holds true here: “A ounce of prevention is worth a pound of cure.” The best cure for white mold is preventing it from growing in the first place.  The worst cause of white mold growth is overwatering your plants.

When to Water Your Plants

Be careful about not only how often and how much you are watering your plant, but also when.  Watering your plants in the evening may be the easiest thing for your schedule, but it is one of the worst times to water.  Soil that gets wet in the evening may not be able to dry out properly in the cooler temperatures overnight.  This is particularly true in the winter when the nights are longer.  Water your plants in the morning before you start your day. This way, the soil has time to dry out in the daylight hours.  And because plants need less water in the winter, make sure you cut back your watering accordingly.  Water your plants don’t absorb is an easy, damp bed for white mold to form.

How to Bottom-Water Your Plants

Another way to prevent white mold from occurring is to water your plants from the bottom rather than the top. White mold generally forms on the topsoil of your plants. So, watering your plants from the bottom will prevent the topsoil from getting too wet. Your plant will still get the water it needs. Plus, bottom watering your plant keeps the plant watered for longer than watering from the top.

To bottom water your plant, fill a container with water and set your plant into it. If your plant has proper drainage (it should!), the water will soak in through the drainage hold. Larger pots need more time and smaller pots less. Your soil should draw what it needs in about 15 minutes. Then you can place your plant back in its favorite window.

Cure

Once white mold has taken root, steps should be taken to avoid future problems or contaminating other household plants.

Scouring the Soil

The easiest and most effective way to get rid of white mold is to scoop out the top layer of soil and throw it away. White mold most commonly takes root in the top one inch of soil. So, throwing away that top layer where the white mold is growing will get rid of that pesky problem quickly. You can then replace that layer with more soil. However, scouring the top inch of your plant’s soil might not always be an option. It may be dangerous to young plants or plants in smaller pots where there’s not much soil to begin with.

Treating White Mold with Hydrogen Peroxide

The easiest way to kill white mold on the soil is to allow the soil to dry out for a few days then water your soil with a hydrogen peroxide mixture.  Drying out your soil is key. You need to make sure that you’re not continuing the cycle of overwatering that caused this problem to begin with.

Once the plant is ready for water again, mix one-part hydrogen peroxide with three-parts water in your watering can and water your plants with it. Hydrogen peroxide is not dangerous to your plants in the right quantities. In fact, it can be highly beneficial, providing additional oxygen to your plant’s roots. But too much of a good thing is bad. Be sure you know what percentage of hydrogen peroxide you’re using so you don’t burn your plants. Most hydrogen peroxides purchased at drug stores are a diluted 3%, which works great. If your hydrogen peroxide is more concentrated, use less of it when combining it with water.

You can also pour this mixture into a spray bottle and spray the top of the soil where the mold is growing. If you use the spray bottle option, be careful not to get any on your plants’ leaves if you can. Hydrogen peroxide solution won’t hurt the plant. However, any water on the leaves can be an invitation for other molds to start growing. That creates a whole host of other problems for you and your plant.

Treating White Mold with Vinegar

If used carefully, vinegar can be used to kill mold on plants or plant soil. The difference between hydrogen peroxide and vinegar is that vinegar is much more potent. Vinegar must be diluted much more than hydrogen peroxide.

When using vinegar to kill white mold, mix 1 to 2 teaspoons of either white or apple cider vinegar to 1 gallon of water and spray onto your plant soil once a week. This mixture can also be used on powdery mold which usually attacks plant stems and leaves rather than soil.

If you intend to use white vinegar to kill mold on leaves, be sure to rinse the leaves with water an hour or so after treatment to avoid burning the plant. For this reason, I recommend hydrogen peroxide solution over vinegar solutions.

Treating White Mold with Cinnamon

For the eradication of white mold from your pots you can also sprinkle cinnamon on the topsoil of your planters.  Cinnamon is a natural anti-fungal. It will kill mold, fungus, and mushrooms if applied in a gentle sprinkle along the topsoil.  Cinnamon is also great at preventing damping off of young seedlings, as that is also caused by mold and fungus. (I’ve previously mentioned this benefit to seedlings in my post about Starting Seeds Indoors.)

You can use the cinnamon method on its own or use it in conjunction with either hydrogen peroxide or white vinegar solutions for double the effectiveness. If you use both, sprinkle the cinnamon on top first then give the soil the liquid treatment of your choice. This way, the natural antifungal nature of the cinnamon will seep down into the soil.  As previously mentioned, fungus and mold generally only occurs on the top inch or so of soil. Still, you’ll want to make sure it seeps down to every level that you can reach without harming your plants.

In Summary

White mold isn’t a death knell to your plants, but it is unsightly and can lead to greater problems if left untreated. I hope these options work for you and that your plants will grow greener and brighter for it.