Gardening on the Planet, Science Says

The Case Against Earthworms

When I dug in my Berkshire garden this summer I found a host of earthworms.  That, it turns out, is bad.

I was raised to regard earthworms as the gardener’s best friend.  It’s true, these benevolent creatures (or so I regarded them then) aerate the soil with their tunnels and eat organic litter from the surface of the soil, carrying it back underground to excrete it as “castings” that are full of nutrients for plant roots.

My mother, a devoted gardener and my first horticultural instructor, always impressed on me the beneficial role that earthworms play in the garden.  Later, when I had graduated college and was studying horticulture at the New York Botanical Garden, my favorable view of these creatures was reinforced by a book written by no less an authority than Charles Darwin: The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits.  In this book, Darwin cited calculations that the population of earthworms in the average garden numbered some 53,767 per acre and calculated from his own observations that, depending on the quality of the soil, worms deposited as much as 18.2 tons of castings on the surface per acre per year.  Darwin regarded this as marvelously beneficial, which in some settings it is.  But in the northern United States these industrious creatures are a catastrophe from an ecological perspective.

For earthworms are not indigenous to the northern United State; they were wiped out by the glaciers of the last ice age.  And although there are many species of earthworms that are native to the southern parts of our country, most of the ones we find up here are introductions from Europe or Asia.  Native or foreign, though, earthworms can have dramatic effects in changing the quality of the soil, consuming and decomposing much of its organic content.

This transformation has an adverse effect on native vegetation.  Especially harmful are some of the non-native worms, which are enthusiastic and efficient consumers of organic litter on the forest floor.  This layer of fallen leaves and twigs acts as a mulch and a reservoir of nutrients for surface rooted trees, ferns and wildflowers.  Eliminating it can drastically affect the survival of these species.  Nor are the natives the only plants at risk.  I know of one gardener in Connecticut whose woodland perennial garden was overrun by the large, hyper-active Asian earthworms popularly known as “jumping worms” or “crazy snake worms” (Amynthas agrestis).  In a matter of months the shredded oak leaves with which this gardener had mulched her beds disappeared, and the soil was so over-aerated that plant roots dried out.  She no longer mulches – that just incites a worm population explosion — and periodically applies a tea seed meal-based plant food, Early Bird Natural Organic Fertilizer, that is toxic to earthworms.  In this way she keeps the population of jumping worms in check, but she will never eradicate them entirely.

“Crazy snake worm” — note prominent white “clitellum” or ring

It’s easy to introduce earthworms unintentionally to your garden, as I have learned.  The ancestors of mine — ordinary nightcrawlers (Lumbricus terrestris) — probably arrived in some truckload of compost or the decomposed manure I brought in from a horse farm.  My friend in Connecticut suspects that the Asian worms arrived in her garden in the soil around the roots of a plant shared by another gardener or container-grown nursery stock.  Often, though, worms are deliberately introduced.  Left-overs from a fishing trip are dumped into the woods or garden, or worms escape from tubs or beds in which they have been cultivated to help compost kitchen and garden debris.

Hopefully, the cold winters in my zone 5 garden will help to slow the earthworms spread, and I intend to spread the tea seed meal.   I like my woods as they are – worm-free and full of native wildflowers.

Posted by on October 16, 2017 at 11:12 am, in the category Gardening on the Planet, Science Says.
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8 responses to “The Case Against Earthworms”

  1. Linus says:

    Some more on “Early Bird” from AwaytoGarden:

    Q. …that an organic fertilizer for golf-course use has been developed by a company called Ocean Organics Corporation of Ann Arbor, Michigan, and also in Waldoboro, Maine. They’ve developed this organic fertilizer from tea seed meal (an extract of the tea plant), kelp extract, and composted poultry manure. It’s Early Bird™ 3-0-1 Natural Organic Fertilizer, and right now it’s just being used for golf courses, but this is one thing they are doing to try to minimize this problem and have fewer worms—and they’re not talking about just this particular species of worm.

    https://awaytogarden.com/cracked-tomatoes-growing-rhubarb-hot-spots-asian-jumping-worms-stiltgrass-qa-ken-druse/

  2. Chris says:

    Are there sources online or elsewhere, where I can get further information and sources for getting & using tea seed meal? It’s on Alibaba, with a minimum order of a mere one ton, a bit more than needed for my 0.4 acre. Thanks!

    • Glenda Berman says:

      Hi Chris,
      I live in Columbia County and we have seen a huge amount of these worms this year. A few of us are going to try Early Bird in the spring. I called the distributor in Brookfield CT. and it is $85 for 50lbs but there is a delivery fee of $40 for each 50lbs ordered. If enough people got together for an order perhaps we could get it cheaper. How much was the ton? We were going to call golf courses in the area to see if they use it and if they would add onto their order for us. This is the link to the company. From the information that I have the granular works better.
      http://www.metroturfspecialists.com/images/2015_Product_For_Website.pdf

  3. Maryk says:

    Our earthworms in my Berkshire garden are long, fat, and fairly active– will sneakily squirm away if they perceive you– I hope they are not the non-native “jumping worms”! saving grace: local garter snakes, Robins, and a few raptors may be predating them. They are longer and seemingly more aggressive than newts/efts. EEKS!

  4. Chris in PEC says:

    There’s a great discussion about your Rant going on over at the Garden Professor’s Facebook page!
    Thanks (seriously) for opening up this can of ….

  5. Mara says:

    I’ve heard they can’t handle soil that’s too acidic which onions, garlic and lemons are. Might be good to add that kind of stuff to compost? Also they apparently don’t like poison ivy. Go figure.

    https://unclejimswormfarm.com/what-to-not-feed-worms/

  6. Jay says:

    …Oh, it’s not just me then. North of Boston, I’ve observed a drastic population boom in ENORMOUS earthworms this year that are causing the same issues in my gardens. I’ve quite honestly never seen this many before.

    Mulch and compost vanishes rapidly and becomes the resulting loose, over-aerated worm castings that put planting beds in danger of drying out; I nearly lost some dwarf mountain laurels growing under hemlocks. It’s like watering gravel.

    Would holding back on fall mulching until a hard freeze slow them down?

  7. Tibs says:

    Was informed by a friend that her ducks devour these worms. Too big for her chickens.