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Worm castings vs. compost

Effects of worm castings on rootsA few months ago, one of our readers asked why you would compost with worms instead of just making a traditional compost pile, and I answered "Um, well, errr, they're cute?"  (Well, actually, I made something up.)  Since then, I've been delving into the literature to see whether vermicompost (aka worm castings) is the same as traditional compost, and have discovered that there's actually a big difference.

When you look at the basic macronutrient levels found in compost and worm castings, it actually looks like compost is the winner.  NPK values of compost will vary considerably depending on the raw materials you use, but each macronutrient will range from 0.5 to 4% of the compost's weight.  On the other hand, NPK values of worm castings can be as low as 0.1 or as high as 2, again depending on what you feed the worms.

Red wormsDespite the higher NPK values of compost, though, worm castings have a huge positive effect on plant growth.  When up to 20% of the soil consists of worm castings, plants germinate better, grow faster, and produce higher yields.  Why?

The answer is that worm castings are biologically and chemically different from compost or soil.  Worm castings have much higher percentages of humus than either soil or compost, which helps the castings hold more water and stay aerated, while also providing binding sites for micronutrients that would otherwise wash out of soil during heavy rains.  The castings are also chock full of plant growth promoters like cytokinins and auxins, along with increased levels of micronutrients like calcium, magnesium, and sulfur.  Worm castings also host ten to twenty times as much microorganism activity as plain soil.  No wonder a study showed that worm castings produced bigger blueberry plants and higher fruit yields compared to blueberries treated with either cow manure or chemical fertilizers.

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This post is part of our Hands-on Wormkeeping lunchtime series.  Read all of the entries:





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Ooh, ooh, that was me! Anna, making things up! I'm shocked.
Comment by Heather Fri Feb 25 09:50:22 2011
I meant that I made an educated guess.... :-)
Comment by anna Fri Feb 25 20:42:59 2011
What does NPK stand for?
Comment by Anonymous Sat May 24 16:53:59 2014
NPK
Anonymous --- NPK stands for Nitrogen-Phosphorus-Potassium content. It's a common way of measuring the strengths of fertilizers.
Comment by anna Sat May 24 20:23:03 2014