Steps to Sterilize Your Garden Soil

Gardenerdy Staff Oct 28, 2018
Soil sterilization is performed to kill harmful bacteria, fungi, nematodes, plant pathogens and weeds. You can sterilize potting soil and garden soil by means of heat treatment for a specific period. Read on to find out.
Sterilizing baby bottles, glass jars, laboratory equipment or garden tools is not a new concept for us, except that the method may vary for each item. But, what about sterilizing potting soil or garden soil?
Well, sterilization is the single most reliable technique to get rid of disease causing microbes and pathogens from clothes, glassware, tools and even planting soil. It helps in killing harmful microbes, which otherwise can attack host organisms and cause infections.

Benefits of Soil Sterilization

After continuous gardening in the same soil for several years, it is obvious that the soil will contain various strains of pathogenic bacteria, fungi, viruses, insects and nematodes. Hence, the chances of disease infestation in plants grown in the same soil are quite high.
Under such a condition, soil sterilization works and improves the quality of soil. It also aids in controlling weeds by making the weed seeds sterile. Overall, sterilizing soil does save a lot of time and reduces future headaches for gardeners. No wonder, food growers and cultivators prefer sowing seeds and planting plantlets in sterile soil.

How to Sterilize Potting Soil?

Container gardening by using sterilized soil is an easy approach to maintain healthy plants. You can either sow seeds or transplant seedlings directly in the pots containing sterile soil. Unfortunately, the potting mixture labeled as sterile usually comes along with insect eggs, soil fungus and weed seeds.
So, it is good to sterilize soil at home with simple steps. As for the process, it is easy and more importantly, the amount of soil to be treated is manageable. The steps for sterilizing potting soil on your own are explained ahead.
  • Like other sterilization methods, heat is used to make potting soil sterile. And we can sterilize soil at home by using a gas grill or oven. For both the cases, the preparatory steps remain the same. So, you can choose a convenient method.
  • If you are preparing homemade potting mix, do the necessary mixing, i.e., adding peat moss, farmyard compost and manure to the soil. The final amount should be ideally 5 cups. For the ready-made potting media, you can proceed to the next step directly.
  • Fill the potting mixture in a roasting bag. Pour some water (about 1 cup) in the bag and mix thoroughly to make the soil moist (not soggy or wet). Tie the bag properly with a string and allow it to settle over a roasting or meal baking pan.
  • The next step is to poke 2 - 3 small holes on the top side of the bag. These holes allow steam to escape freely and help in reducing pressure buildup inside the bag. In one of the holes, you can insert a meat thermometer, so that it reaches the soil.
  • One word of caution concerning sterilization of potting soil is that the oven or grill temperature should not exceed 180° F. If the temperature reading is above the said limit, some of soil components turn harmful for the plants.
  • If you are using oven, set the temperature and wait for some time, or until the thermometer reading touches 180° F. As for sterilizing soil on a gas grill, it may take about 2 - 2½ hours to reach the desired sterilizing temperature.
  • Make sure you keep a strict watch over the temperature reading. You can continue sterilizing soil at 180 degrees for half an hour or so. Remove soil from the oven or grill, and allow it to cool down for some time.

How to Sterilize Garden Soil?

Sterilization of soil is a standard method for organic farming. For a newbie gardener, making garden soil sterile may sound something weird and challenging. But, it is not so, and you can accomplish the same with basic instructions.
Over here, heat and rays of the sun are used for killing soil-bone microbes. The method is therefore known as solar sterilization or solarization (meaning exposure to sunrays). If you want to sterilize garden soil by solarization, refer to the following step-by-step guidelines.
  • This process is best done during summer time, when the day temperature reading is at its peak. As expected, solar sterilization of garden soil may take longer time in cold regions. First of all, get rid of those unwanted weeds and remove large debris.
  • Rototill the garden soil, which you want to sterilize. If you cannot manage it, you can skip this tilling step. Water the soil thoroughly, making sure that water penetrates to 18 inches depth. Following this, cover the whole area with a transparent plastic sheet.
  • In order to fix the plastic at place, you can lay down large bricks in the middle and sides. Leave the plastic for at least 4 weeks period. But, if the climate in your area is cold, extend the sterilization period to 1½ - 2 months.
  • For effective solarization to take place, the recommended temperature is 114° F. You can check the temperature inside the plastic sheet, and see if it reaches the desired temperature range or not. Accordingly, you can adjust the solar sterilization period.
  • By now, the top soil layer is sterilized. To get best results, consider turning the soil. Water evenly and then cover with another plastic sheet. Weigh down the plastic sides and continue solarization for another 4 weeks (1½ - 2 months for cold regions).
Indeed, gardening proceeded with sterile soil is a sure way to prevent soil borne diseases and weed growth. But, the downside story is, it kills beneficial microbes too, which are responsible for enriching soil nutrients.
So, to replenish helpful bacteria and microorganisms, you can supplement soil with sufficient amounts of organic compost. Take good care of your garden plants, and they will grow luxuriantly with least problems.