Of Worms and Fertilizers

Today I’m going to write about fertilizers and worms.  The purpose of this post is not to encourage you to use fertilizers.  I agree wholeheartedly with Linda’s post – we don’t need many of the fertilizers which we’re using.  Still, it’s important to know the facts about anything that you’re doing (or not doing) to and for your garden, and to do them (or not do them) for the right reasons.  With that in mind, I’ve been reading about worms and fertilizers for the last few days and wanted to let all of you know the basics of what I’ve been reading, because it is somewhat contrary to what many gardeners believe.

Before we begin let’s get one thing straight — worms are basically good for your garden and your plants in general.  We like them!

Over the years I’ve heard all kinds of comments about how inorganic fertilizer is bad because it kills worms or drives them away.  For the most part I’ve just accepted these claims as generally true because it seemed to make sense and I didn’t have a reason to study it further (I don’t write about worms much, and I’ve never spent any time doing research on them – still, I have to admit that this is no excuse for ignorance).  The only contrary words I’d ever heard spoken about the reality of what fertilizers do to worm populations had come from a soil scientist friend of mine who told me, in casual conversation, that he didn’t believe that fertilizers were bad for worms at all, except, perhaps in the very short term if they got some fertilizer directly on them.  Rather, he believed that, because fertilizers encouraged the growth of plants, fertilizer use would actually increase worm populations because it would increase their food supply.

After reading through a few papers it looks like my soil scientist friend was right.  Here I’m going to summarize my general impressions about these papers into a few sentences – not exactly fair because the relationship between worms and fertilizers isn’t completely straightforward – but hey, this is a blog!  Basically, if you add fertilizer of any sort to your soil you will ultimately increase worm populations because you will encourage the growth of more plant material.  More plant material, over the course of time, means more organic matter for worms to eat.  Generally organic fertilizers seemed to be preferred by worms (probably because they include lots of organic material along with the nutrients which they offer), but overapplication of fertilizer (organic or inorganic) could be bad for worm populations, at least in the short term.

So, in a nutshell, judicious fertilizer use shouldn’t affect worm populations negatively.  Still, why add fertilizer at all if you can avoid it?  Mulch and compost – worms will definitely enjoy that!

9 thoughts on “Of Worms and Fertilizers”

  1. Should we like worms? Many garden worms are not native and destroy the leaf litter that other soil fauna depend on. Dare I say invasive? Doesn’t seem to be much you could do to to prevent them taking over though.

  2. For better or for worse, worms are here to stay. Systems adapt. I would imagine some soil systems are less conducive to worms that others, and that’s where you might find greater fauna diversity.

  3. I read that releasing worms from your vermiculture container was very, very bad “because of the worm problem.” T
    here was no explanation for this. I didn’t know we had a worm problem! Do you know anything about that?

  4. Penny, I imagine it’s because of the nonnative/invasive issue around worms. But as we know, most earthworms in our gardens aren’t native, anyway. I can’t really see it making the “problem” any worse. There are much, much worse nonnative species to spend our time and energy on.

  5. Funny, I’ve never heard or read those comments about fertilizer killing worms. I assume it was a leap taken from the reality that organic farming methods call on the use of manures over synthetic fertilizers which of course serves the needs of worms very well.

    When I’m working in soil with a high % of organic matter worm populations tend to be high. At what point is organic matter broken down to where it doesn’t nourish worms? I’m guessing that the high populations are due to the productivity of the soil rather than the soil itself as worms can’t eat humus.

  6. I’m not into vermiculture but I’ve read that the worms used aren’t the same species as the ones outside and will not survive if they escape. I’m sure that there are some areas where they can but here in NY they won’t last the winter.

  7. Interesting. I agree with the desire to amend the garden naturally, and to use fertilizers very judiciously. I was not aware that many of the worms in our gardens are not native. I assumed that any worms I saw were helpful in aerating the soil and providing additional nutrients through their excrement. Is this not the case?

    Stan Horst
    Publisher: BetterBenches.com

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