How to Sterilize Soil - Backyard Boss
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How to Sterilize Soil

Lurking in your soil is a host of unwanted creatures such as insect eggs, bad bacteria, fungus, weed seeds, and nematodes. Together, they create a less hospitable environment to grow thriving plants that produce an abundance of flowers, vegetables, and fruits.

As a result, many home gardeners sterilize soil, which besides eliminating destructive invaders can save money. For instance, you won’t have to buy soil every time you start a new gardening project, and a healthier habitat prevents plants from dying. Ready to give it a try? The best time to do this task is before you sew seeds or plant anything.

WHAT YOU NEED

Option 1:

  • Gardening gloves
  • Garden shovel or fork
  • Hose
  • Clear or transparent plastic cover
  • Bricks or stones

Option 2:

  • Bucket or large metal bowl
  • Kettle or saucepan
  • Hand trowel or large stainless steel spoon

Option 3:

  • Oven
  • Large sheet pan
  • Foil
  • Thermometer

Option 4:

  • Microwave-safe container with a cover
  • Cling film (optional)
  • Knife

Option 5:

  • Clear garbage bags
  • Clear garden or garbage bag, 1.5 to 2 mm thickness

OPTION ONE: SOIL SOLARIZATION

Gardener Moulding Soil Near Grass
Image Credits: Greta Hoffman via Pexels

This sterilization method is most effective for heavy soils, such as clay or loam, or a blend of the two. Unlike sandy soils, heavy ones retain more moisture to produce enough steam, which is necessary to eliminate bugs and weeds. It’s best to wait for a really hot summer spell to solarize. Follow these steps:

1. Put on your gloves and remove any debris from the plot you will be sterilizing. Use a garden shovel or fork to break up any clumps.

2. Using a hose, water the soil thoroughly.

3. Cover it with clear or transparent plastic that will permit the sun’s rays to penetrate.

4. Bury the edges of the plastic into the soil, or weigh them down thoroughly with bricks, stones, or planks of wood. Keep the cover on for four to six weeks.

5. Drops of steams will appear on the cover. When you notice there are very few drops on the plastic, remove it and water the soil thoroughly again and cover it again. Repeat this process for about four to six weeks.

6. Remove the plastic cover. Water the soil if it is dry.

OPTION TWO: BOILED WATER

Potted Seedlings 12 on a counter
Image credit: Markus Spiske via Unsplash

Use this method if you are putting young plants or seeds into pots and not using a pre-sterilized potting mix. It is also a useful strategy if you are repotting a frail plant. However, it’s less necessary if you are transplanting a mature plant, which has a stronger ability to fight back against threats in the soil. Freezing the soil before applying boiling water is optional.

1. Fill a kettle or large saucepan with water and let it boil.

2. Have a bucket or large metal bowl ready. Use a hand trowel to scoop out the amount of soil you want to use into the bucket or bowl.

3. Once the water has boiled, pour enough of it over the soil to cover it.

4. Using a large metal spoon or a hand trowel, stir the mixture.

5. Once the soil cools and dries out a little, it’s ready for planting.

6. Thoroughly disinfect pots or containers before adding the sterilized earth.

OPTION THREE: BAKING

Brick outdoor pizza oven
Image credits: Erik Mclean via Unsplash

You can also bake soil in an oven to sterilize it. However, be warned that there will be an unpleasant pong during the process. If you have an outdoor oven, it’s a good idea to use it for this sterilization method.

Be careful not to exceed the recommended temperatures because this can lead to unwanted reactions in soluble salts and minerals in the soil.

1. Preheat your oven to 200 degrees Fahrenheit. If your oven tends to run hot, preheat to 180 degrees Fahrenheit instead.

2. Moisten the soil with water. Don’t soak it.

3. Use a trowel or large stainless steel spoon to scoop the soil onto a large sheet pan. Do not compact the soil.

4. Cover it completely with a sheet of foil.

5. Place the pan into the oven and bake for about 20 minutes.

6. Use a thermometer to check the temperature of the soil. Once it reaches 150 to 180 degrees Fahrenheit, turn off the oven and let the pan rest in the oven until the soil cools to the touch.

7. Keep the soil covered until you are ready to use it.

OPTION FOUR: MICROWAVE METHOD

Microwave door handle and knobs
Image credit: Viktor Hanacek via PicJumbo

If you are in a rush to sterilize soil, a microwave oven will finish the task in no time. However, this works only for small amounts. Keep in mind that, as with a convection oven, this process leaves a bad smell behind. Clean your microwave thoroughly when you are through and leave the door open for a while afterward.

1. Grab a reusable plastic container with a cover.

2. Add the amount of soil you want to use and moisten it. The layer should not be more than 4 inches deep.

3. Check the soil to make sure there are no metallic objects in it.

4. Cover the container with the lid or use cling film if you don’t have a cover. Use a knife to poke a few small holes in the lid or film to let steam escape.

5. Put the container in the microwave and heat at full power until the temperature of the soil reaches 180 degrees. This should take about 90 seconds to two minutes, depending on your oven.

6. Replace the lid or film after checking the temperature. Keep the container covered while the soil cools and then it’s ready to use.

OPTION FIVE: USE A GARDEN OR GARBAGE BAG

Gardening Hand Trowel and Fork Standing in Garden Soil
Image credits: cjp via Canva

Your mission couldn’t get easier than with this method. Again, it takes advantage of solar rays to kill pests, fungi, bacteria, and other undesirables.

1. Take a clear garbage or garden bag of medium thickness (1.5 to 2 millimeters) and add moistened soil to it. Do not fill the bag. There should be enough room for you to lay it flat to expose more of the soil at once to the sun’s toasty rays. Tightly close the bag.

2. Lay the bag flat in a very sunny spot in your garden for about four to six weeks.

FINAL THOUGHTS ON STERILIZING SOIL

While there is debate about whether it is necessary to sterilize soil, many home gardeners swear by these methods. If you are worried that sterilization will kill off all the good microorganisms, not to worry. Some beneficial bacteria and even earthworms survive methods like solarization. Also, additives such as organic compost or mulch will quickly replenish healthy microbes.

So, on which side of the debate do you fall? To sterilize soil or not to sterilize? That is the question. Share with us below.

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