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[Roze]

Potting soil is sterilized to give your plants the best growing environment possible by killing weed seeds or disease organisms that might be lingering in the soil. Most commercial products have already done this but if you want to use that rich dark gold right from your garden or reuse what you have, here are a few different ways you can do it yourself:

Oven Method: (small batch)
 

• Fill an ovenproof container about 3 inches deep with soil, mix in a generous amount of water (not enough to make it runny or soupy but thoroughly wet) then cover with aluminum foil.
• Bake in a preheated oven (200°F) until the temperature of the center reaches 180°F (use a meat thermometer to measure). Once the temperature reaches 180°F, bake for 30 minutes.
• Do not overheat or overbake since it can release toxins harmful to plants as well as kill beneficial organisms
• It can smell quite foul when baking, this is normal.

Microwave Method: (small batch)

• To use the microwave, put about 2 pounds of moist soil in a thick, plastic bag. Leave the top open and place it in the center of the microwave.
• Heat it for two to five minutes on full power, checking the temperature in the middle of the dirt with a thermometer. When the target is reached (180°F to 200°F), close the bag carefully and put in a cooler to hold the heat in.

Sun Method: (large batches)

• Choose a spot in the yard that receives at least 6 hours of sun during the day (8 hours a day is best)
• Lay out clear plastic sheeting and cover with a layer of dirt about 4 inches deep. Spray generously with water (not so much that it becomes runny muck).
• Cover with another sheet of clear plastic and secure the plastic in place by laying a border of rocks all along the edges of the plastic.
• Bake in the sun for at least 4 weeks in hot, sunny weather and up to 6 or 8 weeks in cooler weather (this technique is only good for summer). 
• Rake up the dirt each week to make sure the heat reaches all of it.

Tips:

• Reusing potting soil is fine when using with mature plants, though new seedlings or bedding plants require sterilized to have the best chance to thrive.
• Don’t use dirt straight from the garden for a potting medium (alone), mix it with other ingredients to make it lighter and more beneficial for your plants (see below for a few recipes).
• After completing one of the methods above, the dirt will likely be hard and clumpy. Break it down first before mixing with other ingredients
• Make sure that potting containers themselves are clean since they can also harbor disease organisms. You can wash the containers in a bleach and water solution
• You can use these same methods for used potting soil and sand

Happy growing!

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[BubbleCat]

I made baaaad experience in the microwave, I tend to use a big pot, fill it with soil and adequate water, cook it with a lid for long. It always worked, plants seem to not care and contaminants are effectively killed.

1 Like Radium likes this.

[happyconcacti]

I know this is a bit nit-picky (concerned with insignificant details) but the techniques described above are pasteurization, not sterilization.

Pasteurization: raising a medium to about 170F (77C) to kill the majority of susceptible organisms.

Sterilization: raising a medium to about 250F (122C) to kill all organisms.


Hcc

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