“Soil is meant to be dirty!” There is a common perception that most of us hold, and based on this, we use unsterilized soil without thinking of its possible consequences. Well, the reality is far from this.
Any soil is not meant to be 100% clean but sterilized. Therefore, it is wrong to think that soil can be used as it is. We are not denying that you cannot use soil without sterilizing it but only when you don’t care about bugs, weeds, and other pathogens affecting your plants.
If you hear the term “soil sterilization” for the first time, this post is definitely for you. This article specifically sheds light on sterilizing potting soil and DIY ideas that make it possible.
So please don’t skip any section, as we will detail everything about potting soil sterilization methods.
What is Potting Soil?
First thing first- what is potting soil?
Whether you call it potting soil or potting mix, it’s a medium for growing plants in a vessel or pot. In other words, since the soil is primarily used in pots, it is called potting soil.
It would be best to remember that there is no such thing as a single variety of potting soil. Instead, different plants necessitate different types of potting soil, which you can simply obtain at a local garden center.
Fertilizers, organic plants, animal-based materials, inorganic materials, and other additives make up a highly fertile potting soil. Therefore, it is usually advisable to use potting soil only after fully sterilizing it, regardless of the type.
With this, we proceed to the next section to understand the concept of sterilizing potting soil and its needs.
Sterilize Potting Soil- What and Why?
Keeping your plants disease-free requires disinfecting or sterilizing the soil before seeding. It is a method for getting rid of bugs, fungi, soil mites, weeds, and other bacteria present in the soil. Until recently, this practice was generally carried out in professional greenhouses by agricultural farmers until recently. However, soil sterilization has become a widespread practice among home gardeners.
There are multiple good reasons why one should meticulously focus on sterilizing potting soil before growing plants. Below, we have cited some of the top reasons behind potting soil sterilization. These pointers will help you understand the cruciality of the process.
#1. Cures the Soil
When we say sterilization cures the soil, we mean that it aids in eradicating soil problems such as gnats, nematodes, and other pathogens that can cause plant diseases.
#2. Gnat Treatment
That said, gnats are small dark insects found in potting soil that human eyes may miss. Gnats can cause roots to die and stunt plants’ growth. So, if you follow a rigorous sterilization procedure, those insects will be gone in no time.
Apart from gnats, cleansing or sterilizing also helps eliminate soil pathogens. Pathogens are parasitic living entities that rely on a host to thrive. So, if you grow plants in unsterilized potting soil, those pathogens will take up residence in the roots of your plants and feast on them. These creatures will not only hurt a plant, but they will also have an impact on the soil.
So, please do not take the risk and treat the potting soil before transferring them into a planter for growing plants and vegetables.
#4. Prevents Weeds
You are more likely to have weed problems if you use DIY fertilizers. Sterilizing your potting soil will alleviate any weed-related issues, ensuring that your seeds access the best soil nutrients.
#5. Aids in Plant Growth
It has been observed that soil sterilization aids in releasing nitrate in the soil, which is directly effective in boosting the plant’s growth.
Note: It is often stated that sterilization is not a mandate if you plant mature plants. This is so because mature plants are robust enough to withstand the issues with unsterilized soil. Another argument against the soil sterilization process is that it kills good microbes, along with pathogens and gnats, which aid in healthy plant growth.
7 Methods to Sterilize Potting Soil
There is no single method of sterilizing potting soil. Instead, you can do it in multiple ways, depending on your preference and convenience. That said, you can either use chemical treatments or heat treatments.
Note: You don’t have to spend time sterilizing potting soil if you buy it freshly packed with the label “sterilized.” So, if you want to save time, you might want to buy pre-sterilized potting soil from your nearby garden store.
Here is our pick on 7 methods to sterilize potting soil before using it.
Here, we will focus on the sterilization methods involving heat.
The first method we would like to mention is solarization. This process involves harnessing solar power to heat up and sterilize potting or any other kind of soil.
- Clean the soil of debris and other litter.
- Fill the soil in a plastic bag. Ensure that there are no air pockets formed in the plastic bag.
- Irrigate the soil before sealing the bag.
- Hold the plastic bag with anchors.
- Keep the plastic bag with soil outdoors, under full sun exposure, for about 4- 6 weeks.
Note: If you live in a tropical climate, use clear plastic bags to allow the sun’s rays to travel through and not get caught behind them. Use black plastic in colder places to maintain heat better and keep weeds at bay.
Solarization is a time-consuming sterilization process but a safe one that ensures no good microbes are eliminated. However, this method may not be highly suitable to eliminate heat-resistant microbes and aggressive weeds.
#2. Boiling Water
One of the commonest ways to kill soil pathogens is by treating them with boiling water. We can use this method on seed starters, general garden soil, potting mix, and potting soil.
- Pour the soil into a bowl.
- Heat water in a pan and pour it onto the soil.
- Once all the water is poured, and the soil becomes moistened, work it around with a spoon, ladle, or appropriate tool.
- Work on the work continuously to ensure all insects and their eggs are killed.
- Let the soil cool down before using it.
The boiling water method is highly handy and can be used even by novice gardeners.
Note: To ensure that your potting soil is free of diseases and insects, you can employ a double method. It’s the freeze-and-boil technique. You’ll need to freeze the soil by placing it in a plastic bag and freezing it for 4-5 days. Then, as previously said, treat it with boiling water to ensure that the soil is safe to use.
As the boiling water method, steaming is another effective way to sterilize potting soil. You can use a pressure cooker, steamer, or soup pot to carry out this method. However, remember the steaming method can take only a small chunk of soil at a time. Hence, it is a time taking method.
- Take a pressure cooker (or a streamer or soup pot) and place a few cups of water in it.
- Pour a small batch of soil into a clean container and cover its mouth with aluminum foil.
- Place a rack above the water in the cooker, and put the soil-filled container on it.
- Close the lid of the cooker, keeping the steam valve open.
- Turn on the pressure cooker, and let the water boil.
- Once the steam starts to escape, close the steam valve.
- Wait for at least 15 minutes to let the steam build-up for sterilizing the soil inside.
Note: If you use a soup pot, wait for at least 30 minutes.
- Turn the heat off, and let the soil cool down completely before using it.
Did you know you can use your microwave to sterilize soil? Yes, you heard us right! In fact, this is one of the fastest ways to achieve soil sterilization. Follow the procedure mentioned below to accomplish sterilize your potting soil.
You will need moistened soil and a microwave-proof container with a lid to proceed with the method. DO NOT use aluminum foil as the container’s lid in this process.
- Pour the moistened soil into a microwave-proof container and put the lid on.
Note: You can use 1-2lbs of soil at a time. Make sure to dampen the soil to form clumps and not runny.
- Poke a few ventilation holes and keep the lid open for steam escape.
- Place the container in the microwave.
- Turn on the microwave and keep heating the soil until it reaches a temperature of 180 to 200 degrees Fahrenheit.
- To reach the desired temperature, you should heat the soil for 90 to 150 seconds.
- Take the soil out of the microwave and seal the lid completely. If you have ventilation holes, use tapes to cover them up.
- Allow the soil to cool down to room temperature before removing and using it.
#5. Using Oven
If you do not have a microwave but an OTG oven, you can still sterilize your potting soil or potting mix. It is almost similar to the method used for microwaving soil.
Here, also make sure you use moist soil that should easily crumble under pressure. Then, follow the procedure below to learn more.
- Pour the moist soil into a baking tray or container. You can also use a roasting pan for the purpose. Make sure to break any lumps present in the soil.
- Fill the container with a 4″ thick soil layer, and not till the edge.
- Cover the container with aluminum foil to ensure there is no pressure loss.
- In the meantime, put the oven on preheat to a lower temperature.
- Put the container in the oven and set it at 180 degrees Fahrenheit.
Note: The soil should not get hotter than 180 degrees Fahrenheit, or else it will burn.
- Keep the soil in the oven for around 30 minutes. Make sure to maintain the temperature at 180 degrees Fahrenheit throughout the process.
- After the baking is done, remove the soil from the oven and let it sit at room temperature before using.
Caution: Although both the microwave and oven methods are popular in soil sterilization, baking soil can create an unpleasant smell in your kitchen. So, keep your kitchen well-ventilated. Afterward, you can also use a room freshener to freshen up the ambiance.
Chemical methods for sterilizing potting soil are most effective if you need to sterilize large batches of soil at a time. However, using chemicals have some disadvantages, including health hazards and negative impacts on plants.
Still, if you absolutely need to follow the chemical methods to sterilize the soil, here are two of the most popular ones.
#6. Using Hydrogen Peroxide
Using hydrogen peroxide is a common method for sterilizing soil for home gardeners. It is also great for novice gardeners, as it does not involve any technical know-how.
You should follow two steps to do away with the method.
- Take a large-sized bucket. Fill it with water and hydrogen peroxide, and mix the solution thoroughly. The exact amount of hydrogen peroxide will depend on the chemical’s concentration.
- After the combination has been mixed properly, spray it into the soil using a sprayer.
You might be confused about how much hydrogen peroxide should be used at a time. So, here is a tabular form to help guide you in this respect.
|Water Volume||35% Hydrogen Peroxide||3% Hydrogen Peroxide|
|1 quart||½ teaspoon||2 tablespoons|
|1 gallon||2 teaspoons||½ cup|
|5 gallons||3 tablespoons plus one teaspoon||2 and ½ cups|
|10 gallons||6 tablespoons plus two teaspoons||5 cups|
|20 gallons||¾ cup plus one tablespoon plus one teaspoon||10 cups|
#7. Using Formalin
Another chemical that can be used for the same purpose is formalin- a mixture of water and formaldehyde. This can be an effective sterilization technique to eliminate fungus.
- Mix formalin with water in a ratio of 1 part formalin 38% — 40% to 49 parts water.
- When the mixture is ready, soak the land you want to sterilize with it. You must soak the soil thoroughly to reap the benefit of this process. For 1 square yard, you can use around 5 gallons of this mixture.
- Wait for 20- 40 days for the soil to get treated properly and ready to be used for planting.
Note: Use this method only when there is a high temperature; otherwise, the formaldehyde will not work effectively towards fumigating.
So, here we are with our 7 methods to sterilize potting soil that you can use at home. Sterilized soil is a great way to get fresh weed and disease-free soil. It is also highly effective to be used on recycled soil collected from the garden. You can implement any of the methods we have mentioned above as per your need and preference. You do not need to be a pro in gardening to carry on soil sterilization methods. Just remember that heating methods work great on small batches of soil, while chemical methods are ideal if you are planning to sterilize a large amount of soil at a time.
So go ahead, and try it yourself! And do not forget to leave your experience in the comment section below.