Pasteurization destroys most organisms and is done by applying heat until the soil reaches 180°F (82°C) for 30 minutes.
You can sterilize the soil with hydrogen peroxide. Using a spray bottle, saturate the soil with the peroxide solution. Spray until the soil is moist but not soaked, and make sure to spray evenly, paying special attention to the corners. Before using the soil, let the hydrogen peroxide dry.
Sprinkle food-grade diatomaceous earth on the surface of the soil. This natural powder is abrasive to insects and can help kill larvae when they come into contact with it. Apply insecticidal soap or neem oil solution to the soil. These products can help control larvae and are generally safe for indoor plants.
There are many different sterilants you can use for chemical soil sterilization, including formaldehyde, phenols, cresylic acid, ethylene oxide and methyl bromide, though the two most common are sodium azide and propylene oxide.
2 Steps to Gnat-Free
Discard the soil immediately, and replace this top layer with sand, which is free of organic matter and dries out quickly—an unappealing medium for fungus-gnat eggs. Let the soil below dry out completely before the next watering.
Saturate the soil with 1/2 cup hydrogen peroxide 3% per 1 litre water. Put wet soil in a watertight container and leave overnight before planting. This kills pathogens such as fungi and bacteria including insect eggs and nematodes (roundworms).
Steaming: Steaming is considered one of the best ways to sterilize potting soil and should be done for at least 30 minutes or until the temperature reaches 180 degrees F (82 C). Steaming can be done with or without a pressure cooker.
Double 6 - Industrial Strength Soil Sterilant
Double 6 is the strongest and longest-lasting vegetation killer you'll ever need. Double 6 contains a high potency, highly residual additive ensuring that you do the job only once a season. (Control may last up to 3 seasons depending on rainfall).
Even if your bag of potting soil is new, the package could have been sitting outside in the rain at the garden center, harboring pests and disease in a moist environment. An easy way to sterilize your potting soil requires hydrogen peroxide, known for being a disinfectant.
Topped With Diatomaceous Earth
Diatomaceous earth is a non-toxic material that has rough and sharp particles. This makes it able to dehydrate and kill insects trying to pass through it. That's why sprinkling diatomaceous earth over your soil mix helps get rid of any pests living inside.
There are a few reasons why your soil may have bugs. Indoor plants are just as prone to insects as outdoor plants and may even have worse infestations due to the lack of 'good' bugs such as ladybirds who typically remove pests such as aphids and leave your plants alone.
There are two basic methodologies used to sterilize garden soil and sterilize potting soil: chemical treatments and heat treatments.
The best way to sterilize soil at home is by steaming it in the oven or on a grill. Steam sterilization is also popular in commercial farming and greenhouses, but they have a better method for doing it on such a large scale. You'll accomplish this by adding a little water and some heat.
However, the two most common soil-sterilant herbicides encountered in landscape settings are tebuthiuron (Spike) and imazapyr (Arsenal AC).
Our top-recommended bare-ground herbicides are Bromacil 40/40 or Pramitol 25E. Remove emerged weeds with a non-selective weed killer like Glyphosate 4 Plus.
Under most situations we would encounter in an agricultural setting, a pesticide half-life can range from a few hours to 4-5 years. Most pesticides are broken down by microbes in the soil, so environmental conditions that reduce microbial activity (cold, dry conditions) will extend pesticide remaining in the soil.
Soil sterilization modalities with high efficacy at bench-scale include wet and dry heat, metam sodium, chlorine dioxide gas, and activated sodium persulfate. Simple oxidants such as chlorine bleach are ineffective in sterilizing soil.
To kill off most viruses, diseases, fungi, and mold, you need to heat the soil to 145°F for 30 minutes. If you want to eliminate soil-borne insects—which include good guys along with the bad guys—you need to crank up the heat to 160°F.
Of all the methods available for sterilization, moist heat in the form of saturated steam under pressure is the most widely used and the most dependable. Steam sterilization is nontoxic, inexpensive 826, rapidly microbicidal, sporicidal, and rapidly heats and penetrates fabrics (Table 6) 827.
Prevent Fungal Disease
MAKE IT: Mix 1 teaspoon of baking soda and 2-3 drops of liquid soap in 1 liter of water. Spray the solution on the infected plants. Baking soda helps the plants become less acidic and prevents fungal growth.
To get rid of fungus gnats, mix a solution of one part hydrogen peroxide with four parts water. Pour the mixture onto the soil around the infested plant.
Known as a garden helper, Epsom salt is a natural and effective way to provide essential minerals to plants.