Can You Put Potting Soil in Your Compost?


Replacing potting soil is vital for any gardener. As time passes, the nutrients that plants need to thrive will tend to deplete in the soil, making it essential for any gardener to replace their potting soil yearly. To some, this may seem wasteful, and they wonder if you can add that old potting soil to compost. 

You can put your potting soil in your compost if it does not home a diseased plant. Unfortunately, soil can carry diseases through the composting process and pass them on to other plants. However, you can compost healthy potting soil or potting soil that you have sterilized. 

No one wants to waste perfectly good potting soil, especially when you have a recycling mindset. There are methods to ensure that your potting soil won’t go to waste, which are simple to execute. Let’s talk more about putting old soil in your compost, like when to avoid it and how you can do it safely. 

How Can You Safely Put Potting Soil in Your Compost?

You can safely put potting soil in your compost by first sterilizing the soil properly. This process will remove any harmful residual contaminants and unwanted seeds. Once sterilized, the soil will be free from potential contaminants and safe to put in your compost. 

Sterilizing soil is vital for reusing or recycling potting soil that once housed other plants. Replacing soil every year is critical, but throwing it away can feel like a waste. So, sterilize it and put it in your compost to reuse it. 

There are a few different methods you can choose from to sterilize your potting soil before composting. How you choose should depend on the available resources and the amount of soil you need to sterilize. 

A Small Amount of Soil

For a smaller amount of potting soil, you can use a few different methods depending on what you have available. You must follow the batch system to ensure that you destroy all the potential contaminants harbored in your potting soil. You can do this in three ways:

Steam the Soil With a Pressure Cooker 

All you need to do is: 

  1. Place the soil in the cooker along with a good amount of water.
  2. Let the soil and water mix steam for about 30 minutes. This process will steam the soil, ensuring it is sterilized and safe to use in your compost. 

If you’d like a more in-depth guide on how to sterilize soil with boiling water, you could check this article out: Can You Sterilize Soil With Boiling Water?

Use a Conventional Oven To Sterilize the Soil

  1. You will need an oven-safe container material like glass or metal when using the oven. 
  2. Cover the top of the container with aluminum foil 
  3. Bake it at 200 °F (93.33 °C)  for about thirty minutes. Though, you can go longer if you would like. 

Use the Microwave Method

  1. Source a microwave-safe container and fill it with damp soil.
  2. Cover the container with a lid, poking a few holes for ventilation.
  3. You should microwave a small amount of soil for about 90 seconds each time. 

This method will get the job done quickly, but it does limit how much soil you can sterilize at a time. 

It is important to note that these options are convenient and easy, but they can also make your home smell not-so-great. We recommend only using these options if your home has plenty of ventilation and you don’t mind an iffy smell. 

If the scent may linger or bother you, we have another option for you to sterilize your potting soil. 

Sterilizing Larger Amounts of Soil

If you are working with a large amount of soil, the options above may not be ideal or even realistic. While they are a quick way of sterilizing soil, following those processes with a lot of soil can slow you down. So, let’s talk about what to do if you have a lot of soil to sterilize before putting it in your compost. 

This process uses the sun to do all the work for you, though it does take longer than the methods mentioned above. Start by figuring out how you plan to store your soil, then follow these simple steps:  

  1. Lay out a plastic tarp for the soil, or use a plastic bag. No matter which method you choose, ensure the soil is damp before starting the process. 
  2. If you choose the tarp method, ensure enough tarp to cover the top and bottom of the dirt. If you choose the plastic bag method, make sure you leave enough room in the bag for it to close properly. 
  3. Next, find the part of your property that gets the most daily sunlight. You’ll want as much sun as possible to speed up the sterilization process. 
  4. Put your damp potting soil in whichever container you choose. If it is in a bag, make sure you seal the bag. This seal helps steam the soil by keeping the moisture inside. 
  5. This process will take about two to six weeks to fully complete. Once you finish, your soil will be sterilized and ready for your compost.

Two to six weeks is an extended timeframe. So, if you need help recognizing if you have successfully sterilized your soil, check out my article: How to Know If Your Compost Is Weed Free. This article will help guide you through the process in-depth and better understand how to recognize sterilized soil.

What Are the Benefits of Adding Potting Soil to Your Compost?

The benefits of adding potting soil to your compost are that it can help speed up the process of composting and help eliminate odors. Adding potting soil also allows your compost to retain the moisture needed to work quickly and effectively. 

Now that we know how to add potting soil to your compost safely. Let’s talk about the benefits it can bring. 

Accelerating the Process

Adding even a tiny amount of soil to your compost can accelerate the composting process. Potting soil contains the bacteria and fungus needed to expedite the process for you. So, you will probably notice quite a difference in how quickly you can compost when you add soil to it. 

So, if you need to speed up the composting process, potting soil can be a huge help. Just make sure you sterilize it first to ensure there are no harmful bacteria or seeds in the soil that could negatively impact the compost. 

Neutralizing Odors

As organic waste breaks down in composting, it can smell bad. This foul odor is typical in composting as bacteria and even small creatures fester in the bin. Potting soil can add a neutralizing smell to the compost, which helps control those odors. 

If you’re concerned about the smell of composting, sterilize and add potting soil to the mix. This addition will help balance odors and keep your compost smelling more natural than odorous. 

Help Compost Retain Moisture

A critical part of composting is moisture. It is essential to the process. Potting soil can help the compost retain the moisture it needs to work successfully. Many things we put in our compost do not retain water. So, adding potting soil can help hold on to the necessary moisture and keep the composting process working efficiently. 

Are There Any Risks for Putting Potting Soil in Your Compost?

The risks of Putting potting soil in your compost are the potential pathogens and harmful bacteria that may spread. Composting is great for recycling organic material, but it is useless if it contains bacteria and pathogens that can harm other plants. 

First, you should be wary of using potting soil that has held a plant that died. Reusing soil is not a good option because there is a good chance that the pathogens that killed the plant will remain in the soil. 

There are potentially harmful bacteria in potting soil. Like the pathogens that can destroy your plants, harmful bacteria are not something you want to recycle through composting. It can negatively impact your compost. So sterilize the soil first. 

Final Thoughts

While you can put potting soil in your compost, it is essential to do this carefully. Just adding it without sterilization can be dangerous. In this regard, sterilize the soil first, then add it to your compost to help it absorb moisture and combat odors. 

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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