Can You Use Moldy Potting Soil? - Backyard Boss
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Can You Use Moldy Potting Soil?

Soil is one of the primary factors in your plant’s development. However, what would you do if you suddenly noticed that your soil has become moldy? Would you get rid of the plant? Would you keep the plant as is? Is there a solution in the in-between? Most importantly, is mold dangerous or beneficial to our plants? We will answer all of these questions and give you some tips on how to deal with moldy potting soil.

Is Moldy Potting Soil Bad for Your Plants and Can You Use It?

Before deciding on what to do about this issue, find out why your potting soil might be moldy in the first place. The most common type of mold you can see on your potting soil is white mold. It does best in humid conditions and is most commonly seen when there’s over-watering, bad drainage, or impure potting soil. Moreover, it could result from poor aeration or lack of sunlight. Another reason could be the usage of organic fertilizer.

White mold in flower pot in houseplant soil on white background
Image credits: Firn via Shutterstock

What Will Happen If Your Soil is Moldy?

Mold on your potting soil isn’t always a bad thing. It will not damage the plant immediately but is a clear sign that your soil is lacking what it needs to flourish. White mold is called “the litter transformer”. This is due to its ability to consume decaying organic matter and make it into something helpful to the soil. However, this is not to say that you should take no action!

The mold will eventually affect your plants and they will start turning yellow, wilt, or will even die. Thankfully, there are a few easy ways to get rid of mold on your potting soil. So in short, while it isn’t necessarily immediately harmful, it is a good idea to get rid of it. It may fight with your plants for nutrition and it also gives out a very unpleasant smell that no one would like to have in their home or backyard.

How to Deal with Your Moldy Potting Soil

While your first instinct may be to scrape the mold off, there are a few easier and, frankly, more effective ways to remove it. However, before you proceed with them, ensure that you have gloves and a facemask at your disposal. Mold can be quite harmful to humans.

1. Sunlight

Home gardening and flower-growing still-life of flower in pot with watering can garden tools on green grass.
Image credits: Yasonya via Shutterstock

Your first step should be putting the plants in a sunny and well-aerated place. If you’ve caught the mold early, then receiving enough air and sunlight should be enough to make it go away.

2. Repotting

adding plant to a pot
Image credits: cottonbro via Pexels

If putting your plants in a sunny and well-aerated place doesn’t do the job, you should try to take the plants out of the pot and remove the moldy soil, then replace it with a fresh one. Moreover, you will need to clean out the pot very well, to minimize the risk of mold returning.

3. Use a Fungicide

spraying plants
Image credits: Trung Thanh via Unsplash

If neither of the previous ways worked, you should find a fungicide. It will help get rid of any leftover mold. If you aren’t a fan of chemicals, though, and prefer a homemade mixture, you can mix potassium bicarbonate with water and use that. Cinnamon can also be an excellent fungicide.

If you are looking for an overall good fungicide, you should look at the Garden Safe Fungicide spray. It can be used on a wide range of plants and it can be used up to the harvest day. It is a great choice for those of you who are into organic gardening.

If you are looking for a different option that is more budget-friendly, then you should look no further than the Bonide Sulfur Plant Fungicide Dust. It is effective against a lot of insects and diseases and you can use it on fruits, vegetables, and even ornamentals! Moreover, it is safe for animals.

Using an Old Bag of Moldy Potting Soil – Yay or Nay?

Sometimes it may happen so that you draw the short straw and the new bag of potting soil you just purchased turns out to be old and moldy. The question is – do you use that soil or should you toss the bag away?

  • You can use the soil if you are transplanting, planting, or replenishing. All you have to do is mix it up well and massage the mold into the rest of the mix. Another option is to add fresh compost to the mix. Leaving the bag outside under direct sun for a couple of days is also a good way to ensure that it is suitable for use.
  • Don’t use it if you are seed starting. The mold will compete with the plant for nutrients, which will lower its fighting chance and will most often result in its demise.

Preventing Mold Growth

White mold on soil in flower pot
Image credits: 8H via Shutterstock

Mold will never be completely gone because its spores are a component of soil, even though usually quite harmless. While heat, humidity, and lack of good aeration are a hazard to your plant, they can help mold spores thrive and become adult fungi. However, if you follow these steps, you will be on the right track to avoiding them:

1. Water in Moderation

Usually, mold growth in containers is caused by over-watering. Spores are more likely to do well in consistently humid conditions. This is why you should always make sure that the soil in the pot is dry before watering. To check if your plant needs water, stick your finger in the soil about one or two inches deep. Pull your finger out and if the soil feels dry, your plants need water and if it’s moist, check again in 24 hours. To be sure, you can invest in a soil moisture meter, too.

2. Increase the Aeration

Stale environment will help mold thrive. This is why you should place your pots and containers in sunny and well-ventilated areas. If this is not possible, use a fan to help the aeration process.

Frequently Asked Questions

1. Does moldy potting soil hurt plants?

No, mold in your potting soil won’t hurt your plants, but they indicate your plants are lacking the right environment to thrive. Maybe they’re over-watered, they lack proper drainage and air circulation, or they don’t receive the amount of sunlight they need to grow.

2. Why does potting soil in a sealed bag have mold?

If you keep your sealed potting soil bag in a dark, humid environment, it’s likely to attract mold. It’s a good idea to keep sealed potting bags in places where they receive some hours of direct sunlight to keep in dry inside out.

3. A large amount of my plant’s soil is moldy, can it be saved?

In this case, it’s better to repot your plant because clearly there’s something wrong with the soil it’s growing in. After repotting the plant, go back to the pot with moldy soil. Scrap out as much as you can and spread the remaining soil on a clean tarp under the sun. Let it “bake” for a few hours and then add an anti-fungal solution to it. If you don’t have one handy, sprinkle cinnamon or baking soda on the soil. Mix it thoroughly to ensure that the solution, cinnamon or baking soda is evenly distributed. You can continue to semi-bake it under the sun (keeping it in a place that doesn’t receive direct sunlight) to let it dry and aerate before using it again.

4. Is plant mold dangerous for humans?

Always remember to wear your gloves and a mask whenever you’re handling mold. People who’re sensitive to mold can develop allergic reactions soon after touching or accidentally inhaling mold spores. Symptoms include sneezing, runny nose, blood-shot eyes, and possibly some skin rash. People with serious mold allergies must never go near or touch mold without proper gear because it could cause shortness of breath.

Additional Information and Tips

The Plants and Lucia YouTube Channel posted an informative guide to help you get rid of mold in potting soil that you can check out. The Gardening in Canada YouTube Channel also has a video about the fixes and prevention of moldy soil.

In Summary

While the sight of mold in your pot or container can be upsetting and stressful, it does not necessarily mean that your plant is in grave danger yet. All you have to do is ensure that your plant has a lot of sunlight, good airflow, and is not over-watered.

However, if these factors are there, but the mold hasn’t disappeared, maybe a fungicide can help. If you can’t use cinnamon or baking soda, you have the Bonide Sulfur Plant Fungicide Dust as your budget-friendly and very effective option and the Garden Safe Fungicide Spray as your more versatile and slightly more pricey option.

Hopefully, this article has helped you deal with your moldy potting soil and has reassured you. If you have any questions, please leave a comment down below!

Happy Gardening!