In the Garden:
New England
February, 2007
Regional Report

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Help keep worms in our gardens and out of the forests.

The Dark Side of Earthworms

Ask a gardener what creature of the earth does the most to enrich our soil and the answer is most likely to be ... the earthworm. I have a worm-composting bin in my basement not just for recycling food scraps but also for the worm manure or castings that I mix into the soil to benefit my plants. But like many things in life, it turns out that there's no black or white, no "all good" or "all bad." Earthworms, it appears, have a destructive streak.

The earthworm's ability to tunnel through the soil and make passageways for air and water, to decompose organic material and release its nutrients, and essentially "till" the soil is good news for farmers and gardeners who are growing crops that are continually replanted, and where the soil is continually amended. Earthworms essentially prepare the soil for us.

But forest ecosystems are an entirely different matter. There, earthworms are rapidly decomposing the spongy layer of leaves and plant matter that makes up the forest floor. This duff layer is essential to understory flora -- tree seedlings, wildflowers, ferns, and so on, -- and fauna. Earthworms are consuming the duff faster than nature can replace it, leaving little to support and nourish the rich native plant life. Invasive plants, being opportunists, are moving in.

The underlying (no pun intended) problem is that earthworms are not native to most northern parts of the country, including New England. The earthworms in your garden are invasives from Europe that may have arrived with the Colonists (in soil used as ship ballast or with plants) or may have been introduced more recently by fishermen dumping their bait or gardeners spreading compost or mulch, especially worm castings. (Uh oh!) Invasive species of earthworms, much like invasive plant species, cause more harm in wild areas, like the forests, than in cultivated areas.

Redworms or red wigglers, the commonly used composting worms, are invasive, too, but they are not hardy in northern climes and probably won't survive in any worm compost that you add to your garden. But with the warmer-than-normal winters we've been having, this may not be the case for much longer.

Be Mindful
So what can/should gardeners do? The University of Minnesota, which has been a leader in researching and spreading awareness of the problem, has some recommendations (and lots of helpful info) in their Great Lakes Worm Watch (http://www.nrri.umn.edu/worms/action/index.html):

1. Don't dump night crawlers or composting worms or any worms in the woods.
2. Dispose of unwanted fishing bait in the trash.
3. If you use worms for composting and your garden is adjacent to a forested area, play it safe by freezing the compost for at least one week before spreading it in your garden. This will kill the nonnative worms and their cocoons.

What we're learning about earthworms might not come as a surprise to Darwin, who did a lot of thinking and investigation about earthworms. In his book, The Formation of Vegetable Mould, he titled a chapter: "The Part Which Worms Have Played in the Burial of Ancient Buildings." Hopefully we won't need to amend that chapter to include the burial of ancient forests.


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