Episode 342: 7 Ways to Kill Soil 

This is The ChangeUnderground for the 26th of June 2023.

I’m your host, Jon Moore

Decarbonise the Air, Recarbonise the Soil!

As I discussed last month with the new vision statement for the podcast and blog, “Decarbonise the air, recarbonise the soil.”

This week we continue our journey through the soil with a post from CHELSIESQUARED entitled: 7 Ways to Kill Soil Microbes: and why this is a bad idea….  

The author Chelsie Anderson comes to this post from two separate events which were adverse for her worm farm. In one case the worms went walkabout when too many coffee grounds were added to the worm bin. The second was a result of using chemical laden potting material from “off farm”. Earthworms make great canaries, in the sense that miners used to keep canaries to check for poison gas in mines. If the earthworms are leaving, we have a problem.

They will, naturally enough, no pun intended, move away from things that will kill them. And they are sensitive to changes in their homes. They require bedding and food. Should either be out of their comfort zone, they will decamp.

Keeping earthworms has many benefits but as canaries in your soil might be one you hadn’t thought of yet.

Top the seven killers:

  1. Chemicals
    1. This one would seem self-evident. We too can be poisoned by chemicals so it’s not surprising earthworms and other soil biota suffer the same consequences. Now chemicals can cover anything from excessive amounts of coffee to artificial fertilisers. The dose is, of course, important. This is why earthworms and other soil biota can survive low levels of NPK fertilisers. As directed by the manufacturers, they are lethal to soil biota.
  2. Salt
    1. The apocryphal tale of the Romans ploughing the field of Carthage with salt gets the message across. As does sea water inundation in low lying island in the Pacific. Salt will kill soil biota. Salt is also suggested as a “natural” herbicide. Yes salt is natural, yes it will kill weeds and snails and beneficial plants and soil biota and earthworms. It has no place in the soil.
  3. Vinegar
    1. Quote: This is another weed killer. If you buy a horticultural grade vinegar (7-20% vinegar) and spray this on young weeds in the spring, they will die back, at least temporarily. The problem is – vinegar kills indiscriminately, so it will kill other plants if accidentally sprayed, as well as the critters of the soil, including microbes.  End Quote So it is again “natural” but not something to use.
  4. Chlorine
    1. This one is a dosage matters with poison situation. Chlorine gas was used in WW1 to kill humans. It is used in swimming pools to kill  microbes. It is in public water supplies for the same reason. The key words there are to kill microbes. Garden hoses from the mains water supply will contain chlorine. I smell the stuff if I have the first shower in the morning. To avoid this peril in the garden will require some form of rainfall harvesting. I understand this is illegal in some parts of the world. This is to control mosquito breeding places, apparently. The other solution, as suggested by aquarium owners is to let the water stand, uncovered overnight to allow the chlorine to dissipate. Best advice, try to avoid chlorine.
  5. Dehydration
    1. This one is difficult to see, obviously with microscopic biota, but earthworms again act as a canary in the mine. I’ll quote from the piece again: Quote: In a not-so-obvious, but simple way, dehydration kills microbes. You want to preserve those summer berries? Dehydrate them and they will not rot. Soil microbes are no different. While very wet conditions cause anaerobic conditions (smelly and not-so-good bacteria and nematodes to thrive), drought also kills. This is one more reason to use a mulch in summer. Natural mulches prevent topsoil from drying right out, also preserving those beneficial bacteria! End Quote This seems so obvious once said out loud. Some soil biota are capable of surviving droughts by sealing themselves off and waiting for rain but that’s not much help if you’re trying to grow things. For that matter, neither is dry soil. I like the mulch idea, it fits in with the No Bare Soil principle from last week’s episode.
  6. Tilling
    1. Another of the principles from last week. I don’t think I can paraphrase better than Chelsie for this point so here comes a longish quote. Quote: The no-till garden has gained in popularity over the past decade or so and with good reason. Mycorrhizal fungus is an invisible-to-the-human-eye web in the soil that literally feeds your plants the nutrition they need in exchange for the sugars that plants can produce through photosynthesis of the sun. It’s a pretty great mutually beneficial relationship. Plants that have abundant amounts of mycorrhizal fungus are less susceptible to diseases, pest problems and also grow stronger, since they are being well fed. Parent trees can share nutrition with baby saplings using this web as well, in a way nurturing them just as any other living being does. When we till the soil, we break up this invisible web, meaning our plants are left with fewer bodyguards. Only dig when it is necessary (ie- to harvest your potatoes or to plant a seedling. Otherwise, simply top dress your garden with all of the goodies including worm castings, and the microbes will travel to where they want to be in the soil food web.  End Quote. I think we have more than sufficient evidence available to support this idea. By the way I happen to have a No Dig Gardening book for Sale at Amazon and the website. Links in the show notes.
  7. Starvation
    1. This is a thing which becomes second nature once we change our mindsets from feeding plants to feeding the soil. Organic matter and the correct level of moisture will keep our soil beasties alive and well. Mulching, no bare soil and no tillage will all work together to ensure their dietary requirements are met. Again to quote the piece. Quote: Microbes, like anyone else, need carbohydrates. Naturally they’d get them from plants (photosynthesis produces sugars) to keep them going. If you have a bare patch of soil with no plants, then there will be no food. You can artificially add carbs to their habitat through sprinkling the ground with finely milled flour for example, or by mixing molasses into water and applying this. Or you can simply allow plants to grow as they will feed the system naturally. Does this help explain why bare ground doesn’t stay bare for long? End Quote.

So in summary these are the things to avoid to keep your soil microbial community happy, thriving and alive.

  1. Chemicals
  2. Salt
  3. Vinegar
  4. Chlorine
  5. Dehydration
  6. Tilling &
  7. Starvation.

And with that I’ll draw this episode to a conclusion. Remember: Decarbonise the air, recarbonise the soil!

Thank you for listening and I’ll be back next week.



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7 Ways to Kill Soil Microbes: and why this is a bad idea!



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