Soil sterilization is a great technique for organic gardeners to master.For potting soil, you will need a sterile mix to avoid bringing weeds and pathogens into your indoor plants. You may also wish to sterilize outside soil if you wish to start over on a patch of garden. Here is why you might want to sterilize soil, how you can do it and how you build up a healthy population of beneficial organisms after you sterilize the soil.

Soil is full of living things: bacteria, fungi, worms and insects. Many of the organisms in soil help break down larger pieces of organic matter like grass, twigs and bark into small particles of humus, which is the best substance you can have in the soil. These organisms also break down nutrients into forms that plants can more easily take up through their roots. Thats the good part about the living things in soil.

The bad part about living things in soil is that there can be detrimental fungi, bacteria and insects in the soil along with the beneficials. In most garden soil, there is also an abundance of weed seeds. If you are gardening organically, from start to finish, and need to create a new flower bed, one way to rid the bed of weeds is to sterilize the soil. Doing this can save you lots of time and money in the long run. If you are starting your own seeds, you need sterile potting mix so that seedlings do not succumb to damping off, and other life-ending diseases that plague seedlings grown in un-sterile potting mix.

Garden soil is a bit more difficult to sterilize, but it can be done using a process called solarization. This is a method of using heat from the sun to kill disease organisms that cause plant problems like verticillium wilt, root rot, damping off and others. In order for your garden to have the full benefit of solarization, the soil needs to reach a temperature of 114 degrees F (46 degrees C) for at least four to six weeks. Heres how to solarize your soil:

A few notes about sterilizing garden soil: For the most part, beneficial organisms will survive the solarization. You can add humic acid or compost to the soil to put back in the good stuff after youve solarized. It is not a bad idea to test the compost for weed seeds by watering a little and seeing if it grows. You can water with compost tea to add beneficials back as well.

Solarization goes most quickly in the south, during sunny, dry days. For almost every location, it works best in the summer. If you solarize in the summer, try to leave the soil covered with black plastic during the winter, or plant a thick green mulch crop to build up fertility, and keep weed seeds out until you plant the following spring. (Always remove the plastic before planting!)

This is such an interesting article to read upon. Gardening is really enjoyable thing to do. Other than this, this is an activity that is eco-friendly. By doing so, you are saving our nature and environment and it will provide us with fresher air to inhale and prevent flood to occur.


Yikes, goatheads are horrible to have! If it€™s allowed, I would actually burn them with a propane torch – Katie uses it as part of her weed program –

That looks nasty! You can burn your weeds, solarize, or work on your soil. Im always a fan of working on the soil. Often times, if you have some turf growing, but mostly weeds, the conditions in the soil are better for the weeds to grow than the turf. The way to fix that is to make the soil more hospitable for turf. (Check pH, aerate, add compost, soil test, etc.)

I had no idea I was supposed to be sterilizing my soil.. maybe thats why most of my plants keep dying. I am so thankful for this post– maybe itll turn my gardening season around this spring. Great post!

[…] (haha). Ill be starting my seeds indoors this week. Ive also looked up how to sterilize soil so that I can use it to start my seeds in order to give my plants the best start possible. […]

Dont ever microwave soil. You wont know exactly whats in it, and so there could be some pieces or iron ore, other other metals that will ruin your oven. It also doesnt cook the soil through and will only heat it in places.

Actually, using your microwave is an entirely appropriate, safe and highly effective method of sterilizing soil. The radiation will effectively kill bugs and pathogens that heat alone wont. To ensure even distribution, irradiate a few cups of soil at a time in a glass or ceramic bowl. For an 1100 watt oven, three minutes on high will be sufficient to kill all living things in the soil. Unless you get your soil from a scrap yard, worrying about it being full of metal is rather paranoid, but if for some reason the soil you chose does contain metal, your microwave will start ‘crackling – simply shut it off, no harm done.

Hi Cheryl, Viruses are different to bacteria in that theyre not truely alive and need another healthy cell to feed off and reproduce. That means that viruses generally dont hang around in soil, but in the plants themselves. Sterilization will kill the virus, but I think youre basically going to have to dig up the infected plants in the area, set up a quarantine (dont plant anything else there for 1-3 months) and then start again. You may have to burn the infected plants if its serious enough – as disposing of them any other way will just spread the virus. – Chris

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