How To Sterilize Soil

Last Updated on October 6, 2021 by Grow with Bovees

Are you struggling to keep your outdoor garden or indoor plants alive and healthy?

Do you feel like you have attempted every care tip in the book but still, fail?

Well, let me ask you this. Have you ever sterilized the soil that you grow your plants in?

Many newbie plant lovers and indoor plant enthusiasts may not know the importance of soil sterilization.

But this process is crucial in order to get rid of or prevent any diseases, pests, weeds or other problems found in unsterile soil that can be very harmful to plants and flowers.

Getting rid of these issues by achieving sterilized soil will make for better and ideal conditions for healthy plant growth.

Even the most skillful plant experts and professional greenskeepers experience these issues, which, furthermore, only lead to disappointment and frustration.

Because coming back from pest infestations that kill or damage crops is extremely difficult.

There are a few different common methods that can be used when aiming to achieve sterilized potting soil as well as pros and cons when starting this process.

Continue on as we take you through all you need to know about soil sterilization methods.

Learning about the dos and don’ts, the pros and cons, the reason why and how to go about this process — just to name a few.

Defining Potting Soil Sterilization

Soil sterilization is a process used in order to eliminate or fend off detrimental garden pests, fungi, viruses, bacteria, fungus gnats and weed roots or weed seeds which can be very damaging to plants and crops.

The two different methods of soil sterilization processes frequently used by — among others — farmers, cultivators and growers, are known as heat processing and chemical processing.

When and Why To Sterilize Potting Soil

The objective of sterilizing soil is to minimise the probability of threats and potentially harmful issues arising in your garden.

This will in turn reduce having to deal with unpredictability during the gardening seasons and enhance plant growth potential.

The sterilization process may also be considered applicable to house plant enthusiasts and smaller cultivation — although there have been many discussions and different opinions on whether it is beneficial to smaller gardens.

Some have said that it is a waste of time due to the minimal benefits, whereas some are worried about the negative impact it may have on the soil.

Others, on the other hand, say that it is of high importance for healthy plant growth, especially when planting in pots or containers with soil.

So when is the right time to sterilize garden soil?

You don’t necessarily have to sterilize soil that is free of pests and diseases.

Neither is it necessary to go about sterilizing potting soil that is freshly bought and unused.

When growing mature plants, it should be remembered that they are often healthy and strong.

Most mature plants are able to handle any problems that may be carried in old soil. This includes pathogens from mineral soil.

Sterilization of the soil may then be decided against.

You do however want to consider starting a sterilization process when reusing potting soil for new baby plants, may it be in pots for indoor use or in outdoor gardens.

This includes germination from seeds, transplanting juvenile plants, stem propagation and propagation of shoot cuttings.

Also, keep sterilization in mind if you have previously had problems with infestations in your garden.

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A good thing to keep in mind when deciding on sterilizing fertile soil is that it may not only destroy bad microorganisms, but it can also get rid of beneficial soil organisms.

Beneficial soil bacteria are of high importance in growing a healthy plant as they aid in the movement of nutrients across the soil.

As with most things in the world of cultivation, soil sterilization comes with its pros and cons.

It is, therefore, crucial to properly follow procedures to gain healthy soil management practices, which in turn reduce the chance of negative outcomes.

Seedlings

A common problem when germinating from seeds is damping-off.

This is when the seedling suddenly starts to wilt and then perishes on the stem.

And this is caused by pathogens inhabiting the soil.

So, to conclude, when growing immature plants, used soil should be sterilized or simply purchase fresh potting mix soil to avoid these issues.

Using store-bought bagged compost or soil makes things easier.

Transplanting Juveniles

Immature young plants are very sensitive and vulnerable plants and are always at a moderate risk of catching soil borne diseases.

When transplanting them into new potting containers, make sure that they are thoroughly clean and do not make use of plant matter, compost from an old homemade compost heap or old potting soil without sterilizing it.

Sterilizing the soil before using it, will demolish any threats such as weeds, viruses and nematodes which are able to cause issues such as blight, verticillium wilt, damping off and fusarium wilt.

They lead to major drawbacks and put your plants’ health at risk.

Chemical Treatment and Processing

Chemical treatment is not a very popular method among homeowners and is often rather used when larger amounts of soil need to be sterilized, in commercial greenhouses, for example.

It is a foolproof method quickly applied to great amounts of mineral soil.

Although easy to use, this method does not come without downsides.

There are a certain number of hazards and costs involved in chemical treatment.

The person applying the chemicals is exposed to health and safety risks and the beneficial range of effects is quite narrow when using a chemical soil sterilizer.

A certain chemical is often seen to eliminate only one individual problem out of a few diseases or pests present.

One should add a thin layer of chemicals and then allow the chemical applications to drain or flush out of the substrate properly before using it again.

This is done by applying a quarantine period.

If procedures aren’t adequately followed, chemical residues may remain in the soil which then could be absorbed by the roots increasing the concentration of chemicals in plant tissue.

Now that we are all aware of the adverse effects of chemical treatments, let us go on and talk about a more commonly used treatment when it comes to home gardening.

Heat Processing

When utilizing heat treatment as a soil sterilization method, steam or dry heat is used to heat through the soil, raising the soil temperature to a level where it becomes fatal to fungal spores and other harmful organisms.

Upholding these temperature ranges for a certain amount of time eventually causes death to damaging weeds and pests.

You will find that the basic principle in most instruction manuals suggests at least 30 minutes of heating moist soil at a certain temperature range in order to eliminate certain organisms.

According to some research, the population of beneficial soil bacteria reduces with heat sterilization, it does not wipe them out completely.

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Heat processing can be subdivided into four categories.

Namely, natural heat from the sun, using a microwave, hot water or steam and using a home oven.

These methods are all a matter of preference. And you should personally choose the most effective method according to you.

Method of Solarization

The solarization method is when the sun’s natural heat is used to sterilize big quantities of soil, for example, fields or entire gardens.

This process is done over a longer period of time. The soil would need a time duration of 4-6 weeks of full direct sunlight exposure the entire time in order for this method to work.

The primary concept of this process is to cover the soil with layers of plastic. After which — if left alone — the suns rays will be absorbed slowly raising the soil’s temperature until it is warm enough to get rid of weed seeds and other pests.

Thus the level of plant health will improve.

There are different ways in which you can induce solarization. You should use one which is to your preference and fits into your budget. The outcome will be the same in all ways.

When working in bigger gardens or out in large fields, cover garden soils entirely with plastic in order for the suns’ energy to be trapped and sterilization to take place.

Great amounts of potting mix can be spread out between the bottom and top layers of plastic sheets to achieve trapped solar energy.

Use transparent plastic when commencing with this process. Plastic that is dark, or black plastic inhibits solar energy from being caught and trapped as it is deflecting rather than absorbing. Using medium thickness plastic is recommended.

Water or Steam Sterilization

Using boiling water is another method of soil sterilization.

Simply add a pale of boiling water to a pot of soil.

Then take a spoon or a similar tool to stir through the moist soil continuously. The hot water should kill any foreign insects and their eggs.

To make sure that the pathogenic soil is completely rid of bugs, freeze the soil for a period of 5 days before pouring boiling water over it.

Putting your soil in a rack and placing it over a pot of boiling water also works well. This process is known as steam sterilization.

Cover the rack of soil with a piece of tin foil in order to trap the steam in it. Steaming your soil for about 30 minutes should do the trick.

Allow the soil to cool down prior to working with it for burning to be avoided.

Oven Sterilization

This is another easy method to use when wanting to get rid of unwanted organisms in your soil mix.

Be sure to open windows when doing this procedure indoors as it lets off an unpleasant odor.

Start by adding a layer of aluminum foil to an oven-safe container, followed by filling the dish with soil.

Add a few cups of water and ensure the mix is moist. Now cover the soil with a second sheet of tin foil. This will allow your soil mix to stay moist, and it will always help with keeping unappealing smells trapped!

Bake for 30 minutes at an oven temperature of no more than 180 degrees Fahrenheit. Any higher temperatures might cause the soil to burn.

Use a meat thermometer or an oven-safe thermometer to determine the temperature of the soil. Make sure that it does not come into contact with the surface of the pan, readings may be inaccurate.

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Using a Microwave

No oven? A microwave works just as well.

Begin by adding moist soil to a microwave-safe container with a tightly sealed lid. Make sure the container has adequate ventilation though ventilation holes in order for the steam to get out.

Microwave your soil for 90 seconds per 1 kg — this is the recommended time.

Note that just like with the baking method, this one may also release a smelly or earthy odor.

After sterilizing, store the soil until the time of usage.

The Pressure Cooker Method

When wanting to sterilize small quantities of soil, this method is the ideal one to use.

Use a heat-proof container and place it into a pressure cooker of your choice after pouring a couple of cups of water into the cooker, filling it with a couple of inches of water first.

Then add 4 cups of potting soil, covering the cooker with its lid. Make sure that the steam valve on the lid is open.

Start boiling the water. When steam is seen coming from the pressure cookers valve, close the valve.

Let the pressure inside the pot build-up for about 15 minutes.

This will sterilize the soil inside the cooker. After 15 minutes, the heat can be switched off. Remember to wait for the soil to cool before handling it.

Supplies Needed

There are different tools and supplies you will need depending on which method you end up choosing.

But there are a few basics that you can get ready while deciding on which method you will make use of.

  • Heat-proof containers or other baking/oven containers.
  • A thermometer that can read temperatures of up to 200 degrees Fahrenheit. A heat-safe thermometer such as a meat thermometer is great as it is easy to stick into a mass of potting mix.
  • Clear plastic wraps or tin foil/aluminum foil.
  • Clean zip-top, plastic bag or regular clean plastic bags

Now that you have your basic equipment, figure out which method you prefer to use and make sure you have the additional tools needed for the specific procedure.

In Conclusion

If you are a plant enthusiast that likes to make use of the same soil multiple times, whether it is for germination, transplanting or propagation, the above-mentioned methods of sterilization are most definitely beneficial to use.

Soil sterilization plays a vital role in healthy growth.

Newly sterilized potting soil will ensure a clean and fresh growing medium for your greens.

With the knowledge about soil sterilization and plant knowledge provided, you should be able to make the sterilization process hassle-free for yourself.

A few things to remember before we end this information manual.

  • Always disinfect used containers before adding fresh potting soil.
  • Sterilize soil before making use of it to reduce the risk of soil pollution.
  • Do not use soil that comes directly from your garden as a medium.
  • Compacted or hard dirt should be broken up to make it lighter and more favorable. Mixing some amounts of loose components will aid in good soil consistency.

Well, there you have it.

All you need to know about how and when to go about sterilizing your potting soil at home.

We hope that this information is helpful and that it will aid in providing all your plants with even, fresh potting soil which is clean and disease-free!