why did fertilizer kill soil worms?
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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!