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

I was shocked to see that for the second time in as many years I had cause my vermiculture worms some major trauma. This, after having the worms for 8 years previously without any drama. The problem? I was starting to come up with my own ideas, I was starting to experiment. Now, perhaps this doesn’t seem like such a bad thing to you, but the torment I caused my worms was such that on round 2, I managed to almost entirely sterilize (kill off all life in) their bins. I eagerly peered into my bins one day to find only just a couple of worms remained, even though only a few days previous there seemed to be tremendous and healthy populations.

As I had done the year before when I added too many coffee grounds and the worms started escaping (they can “run” pretty quick when they want to!) I removed all of the contaminated material and started the bins anew with the few remaining worms. This time, it wasn’t a garbage bag full of coffee grounds, instead I had added the leftover potting mix from my client’s summer petunia display.

Worms need both “bedding” materials, plus food, plus moisture to thrive. Bedding equals peat moss, or corrugated cardboard, shredded newspapers or dry brown leaves from your yard. I cringed at the thought of discarding the remaining potting mix as my client had asked, so instead I brought it home and started adding it in bucketloads to all of my worms bins, which equaled about 10 at the time. Note to self: it is OK to experiment, but try to keep these tests to a small area, perhaps to just 1 bin rather than all of them at once.

Sadly, there was no going back by the time I saw the damage caused, so I opted to remove all contaminated parts and started fresh. The reason for this disaster? Petunias that come from a garden centre are certainly sprayed with chemicals. In fact, I have never heard of “organic” annuals coming from a garden centre. It makes sense that they have to keep their plants in top shape otherwise their entire profit could be lost for the year due to a pest or fungus problem, so I am certainly not pointing fingers. As such, the potting mix was surely contaminated by pesticides (likely insecticides and fungicides to be more specific). I had underestimated the power of pesticides, and had thought that they would have broken down over the course of the summer, or that the worms would be somehow immune to their effects, but I was wrong.

Worms were not the only critters that got murdered that day. Worm bins are an entire ecosystem in and of themselves, which means there is a whole food chain involved that usually includes teeny tiny spring tales and various invisible microbes. The chemicals would have killed the rest of this system as well.

The good news? Within about 18 months I had 3 bins with viable worm populations. Not 10 bins that were stuffed full as before, but 3 with growing populations. The system can recover, ecosystems can return to health, and it was a thrill to witness that life always finds a way. The sight of the worms made me certain the microbes had also returned, as worms do not work alone, in fact they require the help of microbes to convert food scraps into organic and mineral-rich fertilizers.

So that is the first of the 7 ways to kill microbes, chemicals. We now know how valuable microbes are to ecosystems including gardens, so it is surely in our best interest to keep microbes alive. When they are present, our gardens suffer less disease, grow stronger, produce more fruit (and tastier fruit at that!) and attract more of the beneficial critters responsible for a healthy ecosystem. By knowing how to kill microbes, we will also be learning how to keep microbes alive. So here are 7 ways you can kill microbes:

  1. Chemicals, as explained above.

  2. Salt. Now why would I be adding salt to a garden? Maybe it is a deliberate addition? I was once told by a well-intentioned relative that the best was to kill dandelions is to dig them out then to pour salt down the hole. Turns out this is effective dandelion control, but the salt also kills the rest of what existed there; grass, worms and those very beneficial microbes. Maybe the addition of salt to your garden however, is more inadvertent. Perhaps you use a mix of salt and sand to deal with icy patches on your sidewalks in the winter. Then you shovel this salty snow mix onto your garden beds as the winter progresses in order to clear your walkways. Brown patchy grass and dead perennials in spring will indicate intolerance to this practice and may make you rethink your winter deicing regime.

  3. Vinegar. 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 the same as above however; vinegar kills indiscriminately, so it will kill other plants if accidentally sprayed, as well as the critters of the soil, including microbes.

  4. Chlorine. Chlorine is added to swimming pools and to our drinking water for the same reason; it kills microbes! The water that comes out of our hoses in the summer is full of chlorine, just take a sniff. So, if you use this type of water for irrigating, expect the microbe populations to suffer.

  5. Dehydration. 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 top soil from drying right out, also preserving those beneficial bacteria!

  6. Tilling. The no-till garden has gained in popularity over the past decade or so and with good reason. Myccorhizal 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 myccorhizal 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 its young. When we till the soil, we break up this invisible web, meaning our plants are left with fewer body guards. 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.

  7. Starving. Last but not least you can starve a microbe, or billions at once as they tend to travel in packs of billions! Are microbes starting to sound like they have similar needs to those of all other sentient beings? Hmm, this is no coincidence. 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? Weeds are usually the first to come in, helping to amend the soil… but that’s another story!

The intention of this blog is to encourage people to look after soil microbes rather than kill them (as we often do accidentally). Life in the soil, aka microbes, are responsible for raising up our plants, flowers and vegetable crops. Without microbes our plants have access to fewer minerals, are more scraggly, produce less fruit (that will also not taste as good) and will attract more pests. Avoid murdering your soil/microbes, instead provide a safe and hospitable environment for these microscopic friends by providing food, water and shelter for these tiny yet impressively hard working critters!

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