How to Sterilize Potting Soil? – 6 Great Methods

For those of us who enjoy gardening and having indoor plants, you need to learn how to sterilize potting soil. Some people might discourage you against sterilizing your homemade potting soil because of various reasons. However, please don’t listen to them, unless you want to have creepy bugs and pathogens all over your house.

sterilize potting soil

 

You’ll be forgiven for having thought that soil should be dirty, the truth is that using clean and sterilized soil will do untold good to your plants. Sterilizing potting soil may sound like a sophisticated thing to do but trust me, it’s not. 

Hoping you are a DIY enthusiast and gardener who minds their budget, in this read you’ll get a number of methods on how to sterilizing your potting soil. But, first things first.

plants on sterilized potting soil

What is soil sterilization?

This is a process whereby farmers/gardeners sterilize their soil to control or reduce soil borne pests, insects, pathogens and weeds. It’s a way cheaper process than potentially losing an entire plant. Soil sterilization plays a critical role during seed germination and it’s worth investing in for its large benefits.

Reasons why you should sterilize potting soil

  • It saves you money: Buying clean potting mix every time you want to plant seeds or transplants can be a bit pricey. By opting for soil sterilization, you’ll be surprised at how much you will be able to save.
  • Prevents Damping off of new seedlings. 
  • Lesser chances of weeds sprouting up: This usually happen if you’re using homemade compost. Sterilizing your potting soil will reduce these problems thus ensuring optimal soil nutrients for your seeds.
  • It eradicates fungus gnats: These small insects that normally hide in the soil can cause problems to your plants. They have even been reported in fresh potting soil bought from the store. Undoubtedly, you don’t want your plants to interact with them. Therefore, sterilize your potting soil and see your plants thank you for it.
  • It eliminates the pathogens: There are myriads of harmful bacteria, viruses and other microorganisms that live in unsterilized soil. They can be transferred from one plant to another thus continued harm to you plants. Instead of risking the health of your delicate plants, eliminate them by sterilizing your potting soil before you plant. 
  • It generates ideal conditions for plant growth and development in the soil.
  • It helps the release of nitrate to encourage the plant growth potential.
  • It promotes high-quality produce.
  • Reduce manual labor.

Truth be told, sterilized potting soil isn’t perfect. As a matter of facts, you won’t get the optimal best possible plants with it. However, you don’t want to cope with those creepy crawlies out of unsterilized soil, isn’t it? Obviously, there are pros and cons of soils sterilization depending on the method used. Ensure you follow the required procedures to minimize negative outcomes. 

The following are the materials you’ll likely need for most of the soil sterilization method here-under:

  • Materilas for soil sterilizationGas GRILL/Oven
  • Large Roasting Pan/ Baking Sheet 
  • Mixing Spoon
  • Meat Thermometer
  • Fertile Soil
  • Aluminum Foil
  • Water

How to sterilize potting soil?

As there is more than one way to skin a cat, there are also a number of good ways to sterilize potting soil. Whether you have some soil from your garden of just bought some potting mix from a store, always sterilize it before planting. 

Choosing the right method to sterilize potting soil highly depends on the amount you’re working with and how fast you want the process done. Use any of this methods, the end justifies the means.

1. Boiled water

Procedure

  • Place the soil you want to sterilize into a bowl.
  • Put water in a pail, boil it and then pour it over the soil on the bowl.

Mixing boiled water with soil on the bowl

  • Work the moistened soil around with a spoon or other appropriate tool.

moistened soil

That’s quite simple, right? The hot water sterilizes the soil by killing any insects therein together with their eggs. Your soil is now good for planting.

Secret Sauce: You can use this method alongside freezing. Freeze the soil for about five days and then sterilize it by pouring the boiling water over it. We encourage this method to ensure you completely kill the insects and pathogens thus making your soil completely safe for use. 

2. Use of Steam

This is an equally effective method of sterilizing potting soil.

Procedure

  • Fill a pan with water and bring it to a boil. You can close the lid for faster boiling.
  • Place the soil in rack above the pan. Cover it with a foil. We encourage this since it helps contain the steam and helps sterilize the soil completely.
  • Once the water boils, let the steam escape through small opening leading to the layers of soil.
  •  Let the water continue boiling for about 30 minutes.

boiling water

This will kill any unwanted organisms in the soil mix. Ensure you allow the sterilized soil to cool before handling, in order to avoid any burns. 

After it is completely cool, store it in clean plastic bags or store it in the foiled containers until when you are ready to use it for planting.

3. Use of gas grill

Sterilizing potting soil using this method is quite easy. However, you may need to do it in an open space, else the smell might not be that appealing for your house. Covering the pan with the foil also plays a big role in containing the odor.

Sterilizing Potting Soil with gas grill

Procedure

  • Place a tin foil on a baking pan.
  • Fill the foil with the soil you want to sterilize.
  • Add some little water to make to moisten the mix.
  • Place a second layer of the tin foil over the soil to prevent it from drying out.
  • Place a meat thermometer into the soil through the tin foil. Ensure it doesn’t reach the bottom of the pan lest the readings will be misleading.
  • Turn on the grill and heat the soil at 180 degrees for approximately 30 minutes. While doing this, maintain the temperatures at around 180 degrees, but, don’t let it surpass that point. Higher temperatures can cause manganese and phototoxity which damages the soil.
  • Cover it with the foil until you’re ready to use it.

The only disadvantage of this method is that overcooking the soil can produce poisonous components that can cause harm to your plants. 

4. Use of a microwave

I bet you didn’t know that you can use a microwave to sterilize soil. Well, now you know it.

Sterilizing Potting Soil using a microwave

Procedure

  • Moisten the soil you want to sterilize.
  • Place it in a ventilated container and cover with a lid. Ensure the container and the lid is safe for microwave usage. The ventilation holes ensure steam can escape.
  • Set the microwave to its optimal setting the heat the soil. 90 seconds for 1Kg of soil is recommended.
  • Finally, remove your soil and store it safely until you’re ready to use it for planting.

Note: Your house may have an unpleasant smell afterwards. As with the grill method, you can use a meat thermometer to ensure its heat doesn’t surpass the recommended temperature.

5. Use of Chemicals

Chemical sterilization is used in large scale agriculture. We wouldn’t recommend using chemicals for sterilizing small-scale soil. Why? Because the usage of chemicals not only put your health at risk but may also affect your plants.

Most chemicals also have compounds that may require you to leave your soil unplanted for a specified period before it’s safe for planting. You don’t require that especially if you were in a ‘hurry’ to plant, isn’t it? Anyway, if chemical-free methods of soil sterilization are equally effective and probably cheaper, why put your plants and your own health at risk?

6. Solarization/Sterilizing soil with sun

Evidently, this method is not for the impatient lot. It may take up to six weeks to completely sterilize you soil. In cloudy weather conditions, that may go up to ten weeks. So if you opt for this method, be patient.

Procedure

  • Get a thin layer of plastic and spread your soil on it. The size of plastic material depends on the amount of soil you wish to sterilize.
  • Maintain a thin layer of your soil, not more than a few inches deep. This helps quicken the process.

Sterilizing soil with sun

Major drawbacks are the long duration and the hefty costs incurred in purchasing the plastic.

What to do after sterilizing potting soil

  • Disinfect the potting containers after use and before re-use to ensure there are no harmful micro-organisms hiding inside.
  • Never use soil collected directly from the garden as a potting medium. Always sterilize it using any of the above hassle-free methods to avoid the risks of any sort of contamination. 
  • Practice proper crop rotation.
  • Follow a regular weeding schedule

crop on sterilize potting soil

Parting Shot…

When it’s all said and done, don’t be one of those people who re-use potting soil without considering the effects of the many pathogens, fungus and insects that it may contain. Please note that even fresh potting soil from the store could be contaminated. Therefore, always ensure you use any of the highlighted methods to sterilize potting soil. This will eradicate all the unwanted organisms and weeds from your soil thus optimal benefit to your plants. Your plants will thank you for this.

About Jennifer Igra

Growing up in Brooklyn, New York City known for it’s green gardens. Jennifer, a 30 year old gardener and green living fanatic started Igra World to share her gardening journey and increase gardening awareness among masses. Follow Igra World to improve your gardening skills.

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