two seedlings germinating on sterilized soil

How To Sterilize Soil: how to make your own

Gardening can be a challenge, but sterilizing soil has been offered up as a solution for various challenges. By learning how to sterilize soil, you can kill weed roots, get rid of fungi and pests, and more. There are pros and cons to sterilizing soil, so it’s important to know when and how to take such actions.

Why would I want to sterilize my soil?

Sterilizing your soil is a common way to overcome the problems associated with soil that is difficult to grow plants in. The problem arises from the high numbers of weeds and pests in the soil.

The difficulties are mostly associated with germinating seedlings in trays or pots. The high population of weeds in the soil makes it very difficult to grow fragile seedlings.

When you feel as though you have tried everything, sterilization may be the best solution.

Sterilizing the soil can kill such things as:

  • Weed roots
  • Fungi
  • Viruses
  • Bacteria
  • Pests

Once the soil is sterilized, it can make it easier for you to grow your crops and plants.

Whether you’re a homeowner with an outdoor garden or you’re an indoor plant enthusiast, there are plenty of reasons to consider using a steam or chemical sterilization method. If you’ve been struggling to get anything to grow or it seems as though young plants are quickly dying, it may be the best solution.

Typical uses of sterilized soil

Typically, you’ll want to use sterilized soil when you’re working with small plants, you have a lot of larvae in the soil, or you’re getting ready to do some serious planting.

You’ll have to weigh the pros and cons to decide if using sterilized soil makes sense. For example, if you have mature plants, it may not be a necessary step. The plants may already be strong and healthy. They’ll be able to overcome any deficiencies that are in the existing soil (either in the pot or in the ground).

If you have young plants that are constantly being threatened by such things as weeds, weed seeds, nematodes, or bacteria, you will want to cleanse the soil so that the plants have a fighting chance of survival.

How to sterilize soil

There are two primary ways to sterilize soil. The first is through heat/steam and the second is through chemicals.

Most people prefer to use steam/heat so that the chemicals don’t taint the plants that are being grown. Further, chemical sterilization is typically only used in large-scale commercial applications.

Sterilizing with steam is the most common option. You can choose to use a pressure cooker or you can heat the soil inside of an oven or microwave.

If you choose to use a pressure cooker, you’ll place several cups of water into the cooker. Then, a shallow pan of soil can be placed on the top rack, covered with foil. Close the lid but allow the steam valve to remain open.

If you don’t choose to use a pressure cooker, you can follow a similar process on the stove so that the water boils under the soil or in the oven.

small amount of sterilized soil in pots
Sterilizing soil is convenient when only small quantities are needed.

If you are only sterilizing a small amount of soil, you can also use the microwave. For this method, you can fill a microwave-safe container with moist soil. Cover using a lid or plastic wrap with ventilation holes. For every pound of soil, microwave for 90 seconds.

Should you have massive amounts of soil to sterilize, you can also harness the power of the sun. Layers of plastic can be placed over the soil so that you can embrace solarization. Thinner layers of soil will work best so that you can get the soil heated as quickly as possible.

Minimum temperature required to sterilize soil

In order to ensure that you have killed off any threats in the soil, you’ll need to ensure that the potting soil reaches a minimum temperature of 180 degrees. Further, that temperature should be maintained for at least 30 minutes.

It’s a good idea to get a thermometer so that you can check the temperature during the steaming process. If you’re not getting the temperature high enough, some of the contaminants may still be present.

Limitations of how much soil can be sterilized

There’s really no limitation to how much soil can be sterilized. But sterilizing soil at home is something that will be done in small quantities. You’ll simply want to consider which method will work best based on how much soil you have.

The primary reason for this is so that you’re not bringing all of the soil into your kitchen to heat using your pressure cooker, oven, or microwave.

Soil solarisation

If you have more than a few pounds of soil, you should consider using soil solarization.

Solarisation is when you cover the soil with clear plastic and use the heat of the sun to control weeds and pests.

This process is also used in agriculture, to add more heat to the soil so crops will grow quicker.

The main difference between the two methods is solarisation is used for large outdoor areas whereas sterilizing is for use in smaller quantities like indoor germination or pot plants.

Does sterilizing soil remove nutrients?

There are mixed thoughts when it comes to how nutrients are impacted by the process of sterilizing the soil. In some instances, it can wipe out all good bacteria and microorganisms.

If your soil is filled with contaminants, you may have no choice but to sterilize. It can be the only way for you to move forward with good plant growth. So, you have to take the good with the bad. Yes, nutrients will be removed. Though, there are plenty of ways for you to add them back in once your soil has been sterilized and you have proper growth happening for your plants.

Can I buy sterilized soil?

Most people believe that sterilized soil is a myth. But many specialist indoor potting mixes have had their contents treated in some way or another. Unfortunately, as soon as there’s a puncture or the bag has been opened, pathogens can enter.

This means that you could spend money on soil labeled as being sterilized without getting the benefits. So always check that your potting mix has not been punctured before use.

Alternatively, you could buy potting soil and sterilize it yourself before putting it into use. Check over the bag before you buy it, too. Opt for a bag that doesn’t have any piercings or holes to limit the potential for pathogens.

Ultimately, sterilized soil offers various benefits. When your soil is riddled with fungus, pests, or other problems, you can heat it to kill off everything harmful. Reusing your soil is cost-effective, so as long as you sterilize it periodically, you can provide a healthy atmosphere to grow your plants.